Technical Analysis: WRC Cars 2017

[Toyoda]

Wondering if we need this for the new 2017 group of cars.

If so my first question would be...

Active diff's

How do they work?
What are the likely adjust-ability before stage/ onstage?
What will be the advantages of a well designed diff?
What driving style should this suit?

Thanks

[itix]

To answer your first question. An active center diff locks up the differential at will with some form of clutch arrangement. When the clutch is closed it will be like having no diff at all. When open, it will behave like a standard open differential.

The benefit from this is that the engine torque will always go where there is grip when the diff is locked. For instance, if you had your back wheels on ice and front wheels on tarmac and an open diff, your rear wheels would spin and you'd go nowhere. If you could lock the diff all of the torque would go to the front wheels and you'd move forwards.

It is the same concept in the WRC cars. Under acceleration the diff would lock up and you'd gain more torque on rear wheels due to the front wheels lifting from acceleration (therefore the rear wheels having better grip).

I am not in any way an expert in how they make their diff maps and based on what sensors, angles, positions etc etc... That's for the real brains to work out but at least I gave you one scenario where it would be beneficial.

[Lundefaret]

To answer your first question. An active center diff locks up the differential at will with some form of clutch arrangement. When the clutch is closed it will be like having no diff at all. When open, it will behave like a standard open differential.

The benefit from this is that the engine torque will always go where there is grip when the diff is locked. For instance, if you had your back wheels on ice and front wheels on tarmac and an open diff, your rear wheels would spin and you'd go nowhere. If you could lock the diff all of the torque would go to the front wheels and you'd move forwards.

It is the same concept in the WRC cars. Under acceleration the diff would lock up and you'd gain more torque on rear wheels due to the front wheels lifting from acceleration (therefore the rear wheels having better grip).

I am not in any way an expert in how they make their diff maps and based on what sensors, angles, positions etc etc... That's for the real brains to work out but at least I gave you one scenario where it would be beneficial.

Hello Itix :)

Everything you have described can be done - and is done - with a passive diff.
The potential in the active diff (an active centre diff in the WRC17) is that you can regulate power transfer any way you want, any time you want, on the background of the mapping.

So with these new active centre diffs the engineers can map the diffs to distribute power between front and rear as they want. And they will use certain sensors to get the raw data (speed, rotation, gear, throttle, braking, etc), and they will map the diff to distribute power in a certain way according to the parameters they set, and the "numbers" they get from the sensors.

The advatage of the active diff is that it is fully adjustable, so a driver can make the car suit him better in stead of battling it (if he has that kind of problem.) And the diff can react before its needed, so its ready from the second its needed, in stead of having the delay of the passive diffs.

[Mirek]

There is also an option to switch maps from inside of the car (if it's allowed like with the old WRC cars) so in case of a sudden rain or any other change of conditons, with a puncture etc. the driver can change the diff mapping.

[itix]

Hello Itix :)

Everything you have described can be done - and is done - with a passive diff.
The potential in the active diff (an active centre diff in the WRC17) is that you can regulate power transfer any way you want, any time you want, on the background of the mapping.

So with these new active centre diffs the engineers can map the diffs to distribute power between front and rear as they want. And they will use certain sensors to get the raw data (speed, rotation, gear, throttle, braking, etc), and they will map the diff to distribute power in a certain way according to the parameters they set, and the "numbers" they get from the sensors.

The advatage of the active diff is that it is fully adjustable, so a driver can make the car suit him better in stead of battling it (if he has that kind of problem.) And the diff can react before its needed, so its ready from the second its needed, in stead of having the delay of the passive diffs.

Hi Lunde :)
So why is the Mitsubishi active center differential called like that? Because it is just a hydraulic clutch pack and nothing else. The active yaw control diff in the same case of Mitsubishi does pretty much what you describe (it's a torque vectoring differential) so you can in the case of the Mitsubishi send power to the right or left rear wheel as you wish.

Shouldn't we call it a torque vectoring differential rather than an active one in that case? I mean a passive differential is what I would call a limited slip differential. You can't really choose when to lock it and when not to.

Edit: forgot to say hi back... Can't be impolite :)

[itix]

There is also an option to switch maps from inside of the car (if it's allowed like with the old WRC cars) so in case of a sudden rain or any other change of conditons, with a puncture etc. the driver can change the diff mapping.
Hi Mirek (equal treatment to everyone :) )
Does that mean the old 99-2010 wrc cars had torque vectoring differentials too?

I remember they had very complicated hydraulic systems with accumulators and everything, and it failed quite often.

All three differentials or just the center differential?

[rage82]

Hi to everybody, the old WRC's had active center differential and they have the option to switch between different mapping according to their need in the particular stage or even in the particular corner as Mirek said.
I think that the Mitsu WRC hasn't an active diff they were using a passive one if I remember correctly


Sent from my X17 using Tapatalk

[itix]

Hi to everybody, the old WRC's had active center differential and they have the option to switch between different mapping according to their need in the particular stage or even in the particular corner as Mirek said.
I think that the Mitsu WRC hasn't an active diff they were using a passive one if I remember correctly


Sent from my X17 using Tapatalk
This makes me even more confused... What would then be a passive center diff? To me it sounds like a standard limited slip diff pretty much.

[Mirek]

Itix, the old WRC active center diffs could change the torque split ratio only indirectly by changing the slip level. The result was similar to what production Evos or Imprezas do but I believe they had more input channels and probably overall higher level of regulation. Dimviii or Br21 could tell You more for sure.

It would be interesting to know what is used in the new cars. I don't have a clue.

By the way have You ever played Richard Burns Rally? It features a simple active differential with a 3D map for settings - first axis is throttle, second axis is brake and third axis is vehicle speed.


Rage82, Mitsubishi Lancer WRC 05 had also active center diff. What it didn't have was active front and rear diff which was still allowed in 2005. The reason was that it was already known that since 2006 front and rear active diffs would have to be replaced with mechanical LSD ones. That's why they decided to use them already in 2005.

[Viking]

This is still a very good explanation of the "old" system


http://wrcbehindthestages.blogspot.no/2011/05/chapter-15-differential-extravaganza.html

[Lundefaret]

This makes me even more confused... What would then be a passive center diff? To me it sounds like a standard limited slip diff pretty much.

Hello again Itix :)

A passive, or mechanical, centre diff is for example a "normal" LSD diff which relies on real time speed differences between the shafts on each side of the clutch plates to generate friction to get the diff to lock.
In a diff like this you adjust the locking mainly by the number and type of friction plates, and ramp angle (on throttle and off throttle.) A steeper ramp angle will generate a higher treshold for the diff to lock, and vica verca.

On an active diff the locking of the diff is not relied on real time shaft speed differences, but by sensor generated input. So you can program the diff to lock/open when you want, no matter differences in shaft speed etc.

In its simples form it would kind of be like programmable ramp angles and preload.

If you take a "simple" road car active diff system like the electronically opperated BMW Xdrive, you could theoretically send all power too one wheel (three active diffs, front, centre and rear). That system is working with electroniv servo motors opening and closing the clutch plates.
A rally active diff works in much the same way, but by using hydraulics instead of electronics to do the locking/opening.
(Edit: BMW Xdrive might not be the best example according to Mirek)

(BTW, its open for any engineer/expert to correct me if Im wrong.)

Edit 1: Added "preload" to the programmable example.

[Mirek]

X-Drive itself can not send 100% of torque on one wheel because it's an electo-magnetic center clutch. Only some cars which have active DPC rear diff can distribute 100% on either one of rear wheels. To my knowledge BMW doesn't use torque vectoring on front axle.

[rage82]

You are right Mirek, I know that the Mitsubishi 2005 has some difference comparing to the other cars but can't remember what exactly was. Thanks for the correction!

[itix]

Took me a while to get around to answering to this one. Sorry about that.

So basically, unless I'm retarded, the old active WRC diffs according to Warmbold, Mirek and Ole-Martin were basically what I thought they were. Actively lockable diffs (I had read the Warmbold article before but forgotten about it).

The diffs as explained by all three of you would mean that power (or torque if I'm allowed to be pedantic) gets sent to the wheels which have grip. They weren't torque vectoring diffs like the rear diff on newer Evos, some Lexuses etc etc. A torque vectoring diff basically locks a clutch pack with a positive or negative gear ratio on it to force one wheel to turn faster than the other (or one axle in the case of a center differential... Although I have yet to hear of a torque vectoring center differential). The Mitsubishi AYC system is a well documented example of this. Some diffs use planetary gears to achieve this (sort of like in an automatic gearbox) although I will admit I haven't fully grasped how yet.

[dimviii]

Mitsubishi acd (active center diff) and ayc rear diff (active yaw control) have both clutch packs which activated hydraulically and planetary gears with crown and pinion.
Mitsubishi diffs are active diffs.
torque vectoring diffs we use to name(as same Ford names) the plated clutch of focus rs ie.

[itix]

The Mitsubishi ones work differently from one another. Basically the center diff locks up (like having no diff at all if you don't factor in clutch slip etc) and the rear one locks up two different gear sets that send torque to the opposite drive shaft forcefully (through increase and decrease in speed on the other drive shaft).

It is true that the Evo 10 (all models) have planetary gears, but the old ones (European and Japanese models) had just a straight gear set with clutch packs and torque distribution level is controlled via clutch pressure.

[br21]

Active diff in that case simply controls the amount of lock between the front and rear axle. Depends on speed difference between those two axles (slip) or throttle position, speed, brake position, etc, etc. It's relatively simple, just mapping of it it's what makes the difference.

[dimviii]

The Mitsubishi ones work differently from one another..
no, all evos work the same, with very little differences.I talk about Evos from 2001 (evo 7) till evo X.


and the rear one locks up two different gear .
no there is not 2 different gears.


It is true that the Evo 10 (all models) have planetary gears, but the old ones (European and Japanese models) had just a straight gear set with clutch packs and torque distribution level is controlled via clutch pressure.

all evos,whatever domestic market they have been build,have at center and rear diff clutch packs AND planetary gears with crown and pinion. Except some versions,usdm and rs versions that have plated limited slip diffs from factory at rear.

[itix]

Active diff in that case simply controls the amount of lock between the front and rear axle. Depends on speed difference between those two axles (slip) or throttle position, speed, brake position, etc, etc. It's relatively simple, just mapping of it it's what makes the difference.
Like I thought all along. People started saying that was not an active diff and that started making me confused. Thanks!

[itix]

no, all evos work the same, with very little differences.I talk about Evos from 2001 (evo 7) till evo X.

I mean that the ACD and AYC diff work differently from each other.

The ACD simply lock up with a clutch pack whereas the AYC have two different clutch packs with different function (to send torque either to the right wheel or the left one).



no there is not 2 different gears.

At least in the old AYC diff there was two separate gear ratios, separate to the pinion and crown plus worm gears and whatever else all the components are called. The separate gear set was spinning freely until you lock either of up the respective clutch packs forcing more torque to one wheel or the other. I don't know the details of the new planetary gear AYC's but yes, the principle is the same. At least the 7 had the old type AYC... I'm pretty sure the 8 and maybe the 9 too had them. If the Evo isn't spec-ed as S-AWC it doesn't have the planetary model (I'm talking about European models now... US ones were never fitted with them for some reason until the Evo X which has the planetary gear AYC).


all evos,whatever domestic market they have been build,have at center and rear diff clutch packs AND planetary gears with crown and pinion. Except some versions,usdm and rs versions that have plated limited slip diffs from factory at rear.

I have never seen or heard of a planetary gear center diff. Planetary gear sets take up quite a lot of space and the center diff plus transfer case has not changed design on the outside as far as I'm aware.

I'd happily change my mind if I'm proven wrong though.

[OldF]

I haven’t looked closer to the AYC before because it looks so complicated to understand. I found some pages which clarified (not completely though) how it’s working. The link below is from a Russian page with nice pics with the route of the torque. https://www.drive2.ru/l/3188140/

Google translated: https://translate.google.com/translate?sl=ru&tl=en&js=y&prev=_t&hl=fi&ie=UTF-8&u=https%3A%2F%2Fwww.drive2.ru%2Fl%2F3188140%2F&edit-text=&act=url

The next one shows the difference between AYC and Super AYC (S-AYC). As I understand the AYC “steals” the torque from the other drive shaft and transfers it via the clutch plates and gears back to input. The S-AYC “steals” the torque from the other drive shaft and transfers it directly to the other drive shaft.
http://media.cylex-uk.co.uk/companies/1320/2483/uploadedfiles/13202483_634522861850200344_super_AYC_spec.pdf

A couple of pics of the S-AYC where you can see more clearly what is connected to what.
http://mmna.wieck.com/releases/6db1181c-b9e9-c13c-8ca5-91324b06fc60

“MMC introduced AYC, the first component system of its type in a production car, in August 1996 (EVO IV). Switching from a bevel gear to a planetary gear differential in January 2003 (EVO VIII) doubled the amount of torque AYC was able to transfer.”

What I don’t know if it is possible with a planetary differential to have a torque split of 50/50. Usually planetary differentials have been used with unequal torque split to have a more rear wheel drive feeling.
http://www.stealth316.com/2-awd3.htm
Front / Rear torque split 45 / 55.

Nice pics where can been seen which gears are connected to which clutch pack.
http://www.techtips.ie/Blue-Print/mitsubishi-aycacd-system-1.pdf

[Fast Eddie WRC]

Re 2017 aero packages... VW are saying the Polo's was kept conservative to be tougher and stay in place over a whole stage, rather than just a few km then be damaged by cutting etc.

Have the other teams homologated too much aero which wont last the distance on the rallies ?

[Mirek]

Only the time will tell.

[Fast Eddie WRC]

Only the time will tell.

Of course. But technically how badly affected is a WRCar by the loss of such large aero... could these more powerful 2017 cars become virtually 'undriveable' ?

[Fast Eddie WRC]

MW on the Fiesta development, including the aero:
http://www.rallysportmag.com.au/home/wrc/11066-feature-malcolm-wilson-explains-2017-fiesta-wrc-development

[Lundefaret]

Of course. But technically how badly affected is a WRCar by the loss of such large aero... could these more powerful 2017 cars become virtually 'undriveable' ?

Look up footage of Neuville in Finland in 2014.

[Fast Eddie WRC]

Look up footage of Neuville in Finland in 2014.

The big crash was in Shakedown with full aero attached. ;)
There's just a clip of him later sliding with no rear wing ... but still on the road.

With the 2017 cars having big aero at both ends surely they could be very unstable if front or rear parts get knocked off...

If the Polo was conservative in its aero to avoid this I assume Ogier will want MSport to make sure the Fiesta is built stronger. Its aero looks the most developed but also the most fragile of the new cars.

[Lundefaret]

The big crash was in Shakedown with full aero attached. ;)
There's just a clip of him later sliding with no rear wing ... but still on the road.

With the 2017 cars having big aero at both ends surely they could be very unstable if front or rear parts get knocked off...

If the Polo was conservative in its aero to avoid this I assume Ogier will want MSport to make sure the Fiesta is built stronger. Its aero looks the most developed but also the most fragile of the new cars.

Well, its the sliding with no rear wing I am reffering to. Even with 16 cars more restrictive aero, we could see how much effect it had.
Loosing a front splitter, or a rear diffusor and rear bumper, wont have as big as an effect, but it will be very noticable.

[SubaruNorway]

Look up footage of Neuville in Finland in 2014.

And Solberg's moment in Mökkiperä. Off at 2:55 and jump at 4:10
I bet a 17' car would be twice as bad as this.
https://www.youtube.com/watch?v=sb3coPiC24w

[Norm75]

The big crash was in Shakedown with full aero attached. ;)


If the Polo was conservative in its aero to avoid this I assume Ogier will want MSport to make sure the Fiesta is built stronger. Its aero looks the most developed but also the most fragile of the new cars.
It looks to me that the rear diffuser on the fiesta has been designed so that if it does break off there is also one designed into the rear bumper that will have an effect with the lower part missing.

I read that Citroen tested a fair bit to see what effect broken bodywork would have on their car. Interesting to see that the bodywork on the c3 changed from more boxy design on front wing similar to other cars, to a simpler flare more similar to their own WTCC car.

[J_n_z]

Fiesta diffuser seems least developed to me. In comparison to Yaris or C3 it looks like being added on an already finished car...
I doubt in big effect of underbody aerodynamic on rough surfaces (that are more likely to damage it), since it needs flat surface to work together, and it works at speed, that is lower on rough roads... Even on fast gravel, I doubt in big diffusor efficiency, because body roll destroys "sealing" on the side of the floor...

I think that rear wing is still the thing aerodynamicwise.

[EstWRC]

Tech analysis: Dissecting the new breed of WRC car, Part 1

http://www.motorsport.com/wrc/news/tech-analysis-dissecting-the-new-breed-of-wrc-car-part-1-861818/

[br21]

thanx for the link, unfortunately most of the things written there are total bullshit

[Fast Eddie WRC]

thanx for the link, unfortunately most of the things written there are total bullshit

No need to be so dismissive and patronising, tell us the things you think are wrong.

[Mirek]

Everything is wrong in the article. It's no technical analysis at all and it's a shame that it's called like that.

[br21]

No need to be so dismissive and patronising, tell us the things you think are wrong.
Like Mirek already wrote... almost all. Starting from current wrc power (R5 cars have over 300hp currently) and total mistaken aero explanation, taking into consideration brake cooling ducts as some aero things, etc, etc.

[Mirek]

One particularly funny thing is fabricating of some aerodynamic function of jack fixture tubes :)

[EstWRC]

Part 2 of bullshit http://www.motorsport.com/wrc/news/tech-analysis-dissecting-the-new-breed-of-wrc-car-part-2-861828/

[Fast Eddie WRC]

@RallyingUK thinks its excellent.

WRC IN 2017: Part Two of some excellent technical analysis of the 2017 WRC cars by @SomersF1 for @Motorsport https://t.co/XaTrPNtpBW

[Mirek]

That just reflects the sorry state of journalism these days.

And the saddest thing is that somebody believes in such analysis...

[seb_sh]

I agree, as an analysis it's utter crap, too bad it's presented as such. As a general explanation and introduction to a layman about the new WRC cars it has some merit, as it compares the road car with the rally car. If they had such a thing for all components (suspension, engine, tyres etc.) it would be a nice resource to show casual fans. But as an analysis it's useless because it compares the WRC to a road car (irrelevant) instead of comparing the different approaches and interpretations of a well defined rule set between each other.

Check this out: http://www.mulsannescorner.com/RCELeMans2016.html
That's how you do aero analysis.

[Mirek]

It's not crap because it compares with the road car. That would be totally ok if what it states was true. The problem is that it isn't.

[dimviii]

That just reflects the sorry state of journalism these days.

And the saddest thing is that somebody believes in such analysis...

I had read this link,when I found it I was eager to read to learn something more,something new.
I didn't learned anything.
Same problem with most journalists.You open a link to learn/know something new and nothing happens.

[N.O.T]

most motorsport journalists want to bother with F1 and what kind of lipstick the ladyboys prefer on race day, where their boyfriends shop and other useless crap. They think that by knowing stupid details they are knowledgeable.

So when they try and bring their homo attitude to a mans sport they mess up big time, of course there are simple town folk and people from small villages that believe them if the article has some nice pictures. but these people usually believe everything, even the news on the TV.

i did not bother with the article the time i saw that has fancy pictures, usually its an indication of crap.

[seb_sh]

It's not crap because it compares with the road car. That would be totally ok if what it states was true. The problem is that it isn't.

Besides that the info is wrong, which i totally agree, it's still useless to compare to the roadcar. The WRC body parts are specially designed and made. Even if take some styling from the road car they should be analysed comparing each other and considering the rules, not "oh from the roadcar they added some bits here and a wing in the back". Of course they have...

[Mirek]

Doing the comparison with the stock car is quite ok from my point of view as the article is meant for the general public and not the race engineers. As such it's also easier job because it requires only basic understanding of the issue (even that is lacking here). For making a real comparison between those new WRC cars one must be a real expert and somebody like that would not write for some online motorsport newspaper but rather sit in an engineering office.

[Fast Eddie WRC]

I know those articles arent super high tech in detail about the aero but I dont see they are so bad.

Can any of you give some examples of what is wrong in those analyses ?

[AndyRAC]

I agree, as an analysis it's utter crap, too bad it's presented as such. As a general explanation and introduction to a layman about the new WRC cars it has some merit, as it compares the road car with the rally car. If they had such a thing for all components (suspension, engine, tyres etc.) it would be a nice resource to show casual fans. But as an analysis it's useless because it compares the WRC to a road car (irrelevant) instead of comparing the different approaches and interpretations of a well defined rule set between each other.

Check this out: http://www.mulsannescorner.com/RCELeMans2016.html
That's how you do aero analysis.

I know this won't be a popular view on here, but Sportscar racing has far better journalism and better analysis than rallying. Where is the rallying equivalent of DSC (DailySportscar, for example?

[Mirek]

I know those articles arent super high tech in detail about the aero but I dont see they are so bad.

Can any of you give some examples of what is wrong in those analyses ?

So You don't mind that it's totally misleading because all the stuff inside is wrong? What does it need to contain to be "bad" for You then?

[N.O.T]

you have to first understand that not all people are high revving mirek... some are simple basic constructions without wanting too much detail that causes confusion in their lives.

then you will not ask these questions.

[Mirek]

I understand that people don't need details but this is not about simplification of details. It's not simplified because it's bollocks.

Here on the forum there are very knowledgeable people who work with the stuff and know it by heart, yet people argue with them about bullshit they do not understand just because it's on a fancy media server. Nobody knows everything, that's natural but it's sad to ignore those who know and who share pieces of their knowledge with us. Don't tell me that somebody who has been on this forum for years hasn't still recognized that Br21 is a person to trust regarding technical stuff.

PS I know I used to argue about things I had no clue about as well. Luckily it gets better with time with me.

[Lundefaret]

I know this won't be a popular view on here, but Sportscar racing has far better journalism and better analysis than rallying. Where is the rallying equivalent of DSC (DailySportscar, for example?

Your on to something VERY important here AndyRAC!
Rallying on the top level (WRC) is very small, and a journalist may know a lot of things, but can't tell them because he or she is too connected, so they can either get reprimands, or be shut out of the sport.

One example: Colin Clark obviously have a great deal of sources in the WRC, and sources are the main source of journalistic leads.
He does his low key "kitchen table ramblings", and announced a big story a short while ago (it was Latvala signing for Toyota), but the episode of Kitchen table was delayed.
Then the news broke other places anyway, but he was quite open about the reason for it being delayed was that Toyota had asked him to delay it.
When you get this kind of "control" over the media, the stories that filter through are not really interesting, and we get them after we have learned from our own sources what has happened.

All sports that are really big have a prying media, that really dig up good stories, because stories is what gather human interest, and has been for 10.000´s of years.

In the silly season we have just been through it has been a crazy amount of rumours, leads etc etc, but very little has surfaced in the main stream motorsport media. So a lot of the big drama - a drama that can attract big audiences - have gone largely unnoticed by the general motorsport public.

So I agree fully with you, the WRC (and rallying) needs a daring news source where hungry and competent journalists dig up good stories, and are not afraid of going in to deep details.

I am not a soccer fan, but if you read soccer journalism it is REALLY nerdy, down to what the players had for breakfast.

In regards to the technical article that is written, well, its no masterpiece. It is very light hearted, and threats fans like they are ignorant. And thus, it wont be very popular.
But if you read the articles on the same web page made on F1 by Giorgo Piola, they are really detailed down to the last centimetre, and thus a great read where you really learn a lot about stuff like areodynamics.

The big differences between the 16 and 17 WRC are basically:
- Aero
- Power
- Diff
- Width
- Weight

All of these subjects are great for going in depth and discover how they affect the car.

Get an engineer to tell us how the new active diffs work.
Talk to some different suppliers about them.
Get an aerodynamicist - for example from the DTM - to explain the new WRC aerodynamics.
Let us know from a damper suppliers what really goes on inside a WRC damper.
Etc etc.

There are so many good stories to write - and thus read. And WRC really need it to grow.

In the WRC the thought have long been that you cater to the general public to try to grow the sport, but that never works. You can off course do that with the events, but you need a really good media to cater for the real fans, and build the fan base out of that.
Just see what they do in NASCAR, and how they present the sport. Its the worlds biggest motorsport BY FAR, and they go in extreme detail with expert commentators, even interviewing the drivers live in the races etc etc.

WRC is heading in to very interesting times, and the new regulations (and getting Sec out of the VW) is a big step forward, but now the media needs to follow :)

[GravelBen]

Just see what they do in NASCAR, and how they present the sport. Its the worlds biggest motorsport BY FAR, and they go in extreme detail with expert commentators, even interviewing the drivers live in the races etc etc.

Similar with the V8 supertaxis, most presenters are ex-drivers (with plenty of banter) and have a decent knowledge of the technical stuff, as well as using experts for more detailed explanations at times.

[Toyoda]

Google trans this, good article, Citroen have done well

http://es.motorsport.com/wrc/news/analisis-tecnico-diseccionando-los-nuevos-wrc-parte-1-865549/

[br21]

Nice with new cars with bigger restrictor is that drivers are able to rev them higher, which makes sound nicer, etc.
Toyota has little bit different ALS sound.
Citroen lower front bumper design seems to be cutting snow much more than others, interesting if it can be an issue.

[dimviii]

copy from French forum,and translated via google translate.

FX Demaison gives his opinion on the WRC 2017 ... Auto-Hebdo (which released a special WRC guide this Wednesday)
This is the opinion of a real engineer ...

So for him the C3 is really very stable with a lot of motricity. From the engine point of view it seems very well armed ...
The i20 is "not bad". This is the one whose body parts will best survive the various shocks. An effort seems to have been made on the chassis, the car is now lower on asphalt, while the old i20 was higher (open door squeezing mode on!).
The base of the Fiesta looks good, but it is not as stable as the C3. In the engine he does not see it at the level of the Citroën, and at the level of the aerottes, the fins bring support but will cost in term of top speed.
The Toyota is far from the engine level, the auto moves a lot and does not give the impression of having a lot of grip. For him it does not offer many possibilities of adjustments at the level of the trains (it means that the French engineers who have largely developed the Citroën, the i20 and the VW fire like to have arms of adjustable lengths to adjust pile- Hair camber, hunting, clamp ...)

[nafpaktos]

really good interview,confirms what almost everyone in this forum believes.

[Sulland]

Your on to something VERY important here AndyRAC!
Rallying on the top level (WRC) is very small, and a journalist may know a lot of things, but can't tell them because he or she is too connected, so they can either get reprimands, or be shut out of the sport.

One example: Colin Clark obviously have a great deal of sources in the WRC, and sources are the main source of journalistic leads.
He does his low key "kitchen table ramblings", and announced a big story a short while ago (it was Latvala signing for Toyota), but the episode of Kitchen table was delayed.
Then the news broke other places anyway, but he was quite open about the reason for it being delayed was that Toyota had asked him to delay it.
When you get this kind of "control" over the media, the stories that filter through are not really interesting, and we get them after we have learned from our own sources what has happened.

All sports that are really big have a prying media, that really dig up good stories, because stories is what gather human interest, and has been for 10.000´s of years.

In the silly season we have just been through it has been a crazy amount of rumours, leads etc etc, but very little has surfaced in the main stream motorsport media. So a lot of the big drama - a drama that can attract big audiences - have gone largely unnoticed by the general motorsport public.

So I agree fully with you, the WRC (and rallying) needs a daring news source where hungry and competent journalists dig up good stories, and are not afraid of going in to deep details.

I am not a soccer fan, but if you read soccer journalism it is REALLY nerdy, down to what the players had for breakfast.

In regards to the technical article that is written, well, its no masterpiece. It is very light hearted, and threats fans like they are ignorant. And thus, it wont be very popular.
But if you read the articles on the same web page made on F1 by Giorgo Piola, they are really detailed down to the last centimetre, and thus a great read where you really learn a lot about stuff like areodynamics.

The big differences between the 16 and 17 WRC are basically:
- Aero
- Power
- Diff
- Width
- Weight

All of these subjects are great for going in depth and discover how they affect the car.

Get an engineer to tell us how the new active diffs work.
Talk to some different suppliers about them.
Get an aerodynamicist - for example from the DTM - to explain the new WRC aerodynamics.
Let us know from a damper suppliers what really goes on inside a WRC damper.
Etc etc.

There are so many good stories to write - and thus read. And WRC really need it to grow.

In the WRC the thought have long been that you cater to the general public to try to grow the sport, but that never works. You can off course do that with the events, but you need a really good media to cater for the real fans, and build the fan base out of that.
Just see what they do in NASCAR, and how they present the sport. Its the worlds biggest motorsport BY FAR, and they go in extreme detail with expert commentators, even interviewing the drivers live in the races etc etc.

WRC is heading in to very interesting times, and the new regulations (and getting Sec out of the VW) is a big step forward, but now the media needs to follow :)

some detail on Citroen here, in thos normally very detailled magazine:
http://www.racecar-engineering.com/cars/citroen-c3-wrc/

More of this!

[jparker]

Nice with new cars with bigger restrictor is that drivers are able to rev them higher, which makes sound nicer, etc.
Toyota has little bit different ALS sound.
Citroen lower front bumper design seems to be cutting snow much more than others, interesting if it can be an issue.

Yes, you are absolutely right. Can that be fixed/adjusted?
Here is confirmation:
https://s25.postimg.org/5k9mfgi2n/Screenshot_2017_01_18_23_33_54.png

[mozesii]

Seems like you are the only one with a solution. Almost everyone else knows what is wrong with the analysis of Matt Somerfield but no one can do any better.
Typical pessimism of hardcore enthusiasts. The future awaits those who are willing to adapt.

[Rally Hokkaido]

This month's Racecar Engineering features a technical analysis of the Hyundai i20 Coupe WRCar.
http://www.racecar-engineering.com/cars/hyundai-i20-coupe-wrc/?platform=hootsuite

Also, they have done one of the Fiesta.
http://www.racecar-engineering.com/cars/ford-fiesta-wrc/?platform=hootsuite

[seb_sh]

Seems like you are the only one with a solution. Almost everyone else knows what is wrong with the analysis of Matt Somerfield but no one can do any better.
Typical pessimism of hardcore enthusiasts. The future awaits those who are willing to adapt.


This month's Racecar Engineering features a technical analysis of the Hyundai i20 Coupe WRCar.
http://www.racecar-engineering.com/cars/hyundai-i20-coupe-wrc/?platform=hootsuite

Also, they have done one of the Fiesta.
http://www.racecar-engineering.com/cars/ford-fiesta-wrc/?platform=hootsuite

There you go, two proper articles instead of that dribble disguised as an analysis.

[dimviii]

which rallies are more demanding at brakes?

http://www.brembo.com/en/company/news/2017-world-rally-championship-brakes

[Mirek]

This month's Racecar Engineering features a technical analysis of the Hyundai i20 Coupe WRCar.
http://www.racecar-engineering.com/cars/hyundai-i20-coupe-wrc/?platform=hootsuite

Also, they have done one of the Fiesta.
http://www.racecar-engineering.com/cars/ford-fiesta-wrc/?platform=hootsuite

Sadly both articles operate with nonsential number about the engine. I understand that the real data are secret but in my opinion it is better not to spread clear nonsense. For example 450 Nm of torque and 380 Hp is mathematically impossible combination unless the engine has it's torque peak at the power peak and only at 6000 rpm.

Otherwise it is nice to see all those detail photos which are very interesting.

[seb_sh]

Article on the Citroen, also from Racecar Engineering: http://www.racecar-engineering.com/cars/citroen-c3-wrc/

[N.O.T]

Article on the Citroen, also from Racecar Engineering: http://www.racecar-engineering.com/cars/citroen-c3-wrc/

so british motorsport journalism is now copy pasting older interviews of team managers and also posting magnified pictures and describing what they see in those pictures like 5 year olds...

As the cherry on top, the person who writes about a rally car has a picture of him inside a single-seater...

why they bother anymore ?

[Mk2 RS2000]

so british motorsport journalism is now copy pasting older interviews of team managers and also posting magnified pictures and describing what they see in those pictures like 5 year olds...

As the cherry on top, the person who writes about a rally car has a picture of him inside a single-seater...

why they bother anymore ?

A very good question, the only possible answer that I can come up with is, "to satisfy the minions with even less intelligence than themselves"

[GravelBen]

which rallies are more demanding at brakes?

http://www.brembo.com/en/company/news/2017-world-rally-championship-brakes

Some interesting stuff, apart from the nonsense about "WRC Plus cars"

[NickRally]

Hi boys and girls, I have been lurking around here for some time, but this is my first post. I work as a design engineer in the motorsport industry and what better place for this first post than in the technical analysis thread.

Mirek’s post inspired me to see how close I can get to a real internal combustion engine power and torque curves using the values of 380hp and 450Nm without actually having the two numbers at the same rpm. The result is not too bad, please see below a graph and tabulated numbers:

1186
1190

This is not dissimilar to modern turbocharged engines, like the ones from the BMW range for example, graphs shown below:

1188
1189

And finally, just to clarify, I am not claiming my graph is what the 2017 WRC engine power curve is, but just to check if the two quoted numbers for the 2017 WRC engines can live together happily.

Regards,
Nick

[Mirek]

The torque and power curves of engines with restrictor look usually different way. Please note that stock engines are not restricted therefore their curves have very different shape. With restrictor the torque usually steadily decreases from its peak so that the power is roughly constant in relatively large power bent. I admit I haven't seen a single dyno chart for 1.6T WRC car but from 2.0 WRC, R5 or gr.N I think I have at least some idea.

This is Fiesta R5 dyno chart (comparison R5 to R5 Evo):

http://www.autosport.cz/img/clanky/b_643bccedc96c51c0f3c041a57082d6da.jpg

The peak power in absolute numbers is around 300 Hp and the torque around 400 Nm if I remember well. The rise of torque with the Evo is caused mainly by turbo pressure tuned closer to the allowed limit.

[Mirek]

The peak torque of Fiesta R5 on the graph is likely higher than I remembered - 420-430 Nm is probably more realistic.

[NickRally]

I would say the combination of the two numbers still looks plausible to me:

1193

Though I agree they would most likely be slightly off the mark for the new WRC cars as absolute numbers.

[br21]

I would say the combination of the two numbers still looks plausible to me:

1193

Though I agree they would most likely be slightly off the mark for the new WRC cars as absolute numbers.

With restrictor those graphs look much different, like Mirek wrote - torque is falling down rapidly after it's peak

[NickRally]

br21 – the torque in both graphs, Mirek’s and the second of my graphs, is falling pretty equally down. According to Mirek, the peak torque value in his graph (there are no Y axis values to derive from the graph) is ~425Nm, while the max power is 300hp, which looking at the X axis, happens to be at 5750rpm, that means 366Nm of torque, so the difference in torque values between max torque and torque at max power is ~59Nm. Now going back to my graph, the max torque is 450Nm and the torque at max power is ~391Nm (assuming max power at 6840rpm to preserve the same velocity in the air restrictor when switching from 33mm to 36mm), so the difference in my graph is 59Nm – not different to Mirek’s graph.

[br21]

reality is torque at 6500rpms in R5 is close to 300Nm, not to 400Nm...

[NickRally]

What size air restrictor is this with?

[OldF]

What size air restrictor is this with?

32 mm

[OldF]

NickRally,

I think Mirek and br21 mean that the torque is not as flat as in your second graph having level torque from 1500 rpm to about 4500 rpm. Below is a dyno graph for a Mitsubishi EVO 9 group N (32 mm restrictor). Not the best example either because these cars had more boost compared to the current ones (max 2,5 bar absolute).

http://i267.photobucket.com/albums/ii284/OkdF/Mitsu_Evo9_grpN_Dyno.jpg

[NickRally]

Thanks OldF. So simple extrapolation from 32mm to 36mm (2017 WRC), would turn the 300Nm into 380Nm for R5 car. Once again, my calcs above do not seem unreasonable. And in any case nobody seems to dispute the 380hp max power for the 2017 WRC cars, which appears to be achieved at around 6500-7000rpm, which in turn using simple maths, translates into 411Nm of torque if the quoted max power was at 6500rpm or 382Nm of torque if quoted max power was at 7000rpm.

[NickRally]

Flatness of my graph - as I pointed out this was identical to Mirek's graph.

[Mirek]

Nick, while I have nothing to convince You about 17 cars I'm pretty sure that the peak torque of new WRC cars is a lot bellow 5000 rpm (Your graph), I guess 3500-4000 rpm could be right and the torque is definitely reasonably higher than from R5 car (Fabia has even higher torque than Fiesta). The R5 engines are half-stock units while WRC engines are purpose-built units designed from scratch.

Also I don't believe that the cars have only 380 Hp. This number apeared when somebody said that the new engines would have 80 Hp more but the key is that 2016 cars never ever had 300 Hp but much more. Again nothing in my hand but I do believe that the true power of 16 cars was something around 340 Hp (2.0 WRC were even stronger, even vintage cars like Octavia or Corolla WRC had real 320-330 Hp). New cars have 19% larger restrictor which might indicate something around 400 Hp.

[stefanvv]

New cars have 19% larger restrictor which might indicate something around 400 Hp.

Well that's not much of an increase from 380. I believed they can come closer to Group B cars - 450 hp.

[br21]

You can clearly see on MSport base R5 to R5 Evo comparision chart which Mirek upload that torque difference between 4500rpm and 6000rpm is some 100Nm... so it's not flat...
Current R5 cars have over 400Nm of torque so 2017 WRC cars with 4mm bigger restrictors, purpose built engines, more advanced technology, etc have much, much more.

[NickRally]

Mirek, I agree with your numbers about the new WRC cars, the 380hp will be below what they actually have at their disposal and as you said the previous generation of WRC cars would have had more than 320hp (as stated on the net) in the first place (just for reference for the wider audience 320x1.19~380)

[krzaki]

br21 could put dyno plot from fiesta r5 ?
I heard you had few r5 on dyno :)

[J_n_z]

What is rev. limit for 17 cars? Is it defined by rules?

[Mirek]

I'm not sure but I guess 7500 stays.

[OldF]

It's 8500 rpm.

http://www.fia.com/regulation/category/119

Technical regulations - Article 255A, page 14.

[Mirek]

If they really have rpm limiter at 8500 (I am not sure if they actually use such high rpm at all) it means that the cars actually have shorter gears than 2016 ones - based on the video with speed gun posted in Monte Carlo thread.

[J_n_z]

It seems logical to me... same engine volume, bigger restrictor (more air), so it works optimal at higher revs...

[Mirek]

Yes but 8500 is quite extreme and I somehow doubt that such high rpm are useful while being problematic for reliability.

[J_n_z]

I have no special engine knowledge just little more than basic thermodynamics so... Reliability from which reason?
Simply moving to fast or thermal stress on engine parts, oil...?

[Mirek]

I am also no engine engineer but all S2000 teams had issues with broken valve springs (partially due to the rules - too heavy valves), also connecting rods are stressed very much by high piston speed (due to piston acceleration).

[dimviii]

1,6 lit ,36mm restrictor and 8500rpm will be usefull only at big straights when you want as much possible km/h.

[Sulland]

I am also no engine engineer but all S2000 teams had issues with broken valve springs (partially due to the rules - too heavy valves), also connecting rods are stressed very much by high piston speed (due to piston acceleration).

Are the teams allowed to use lighter valves on the WRC 2017 generation, to avoid valveflow?

[Mirek]

I'm sorry, my English is probably not good enough, but I don't know what You mean by valveflow.

Anyway I don't know the exact WRC rules.

AFAIK the problem with S2000 valves was that they had to be made of steel, i.e. they were heavy. With such high engine speed the valve springs had to cope with very high valve inertia. For me it is an example of a wrong idea how to make things cheaper.

Dim: That's exactly what I though - if the higher top speed as the only clear benefit is worth the effort to make the engine reliable at so high rpm. Maybe they simply set the limiter to lower value than what is allowed by the rules.

[janvanvurpa]

I am also no engine engineer but all S2000 teams had issues with broken valve springs (partially due to the rules - too heavy valves), also connecting rods are stressed very much by high piston speed (due to piston acceleration).


Mirek my dear friend,

Maybe you're not engine engineer but you don't have to be to think...These are 2000cc motors maybe 81mm bore..that means there is only room for 2 x what size valve? Whatever it is, not very big. And if its not very big then even if it had a "big" fat 7mm valve stem like oh, I dunno, the "safe past 9500 rpm ancient old 1970s Ford Cosworth BDG" it wouldn't weigh "that much".

Now I will bet the valve stems are 5,5mm or maximum 6mm , but probably 5,5mm---that means, even in steel, it weight less than old BDA valve...

PLENTY little street car Hondas live just fine at or above 8500 rpm..

Valve failures in all liklihood came from design choice, making them super lightweight not too heavy..

High piston speed...there you can look at the general trend toward longer stroke---because smaller bores..

Smaller bores is driven by traverse engine mounting to some degree (Honda mentioned that last century, first in their inlne 4 bikes --its narrower, then in their CVCC traverse engines "shorter engine fits better when sideways than big bore" they said.) and burn efficiency (takes less time to burn 41-42mm from center (in 4v pent roof head with the sparkie plug right in the middle) than it takes to burn across 90 or 94mm or 96mm with a plug waaaaay over on the side) old school stuff like I build.. This smaller bore thing is a big part of why these modern motors can have scary high compression AND on turbo motors, high boost.

Design choices..8500 isn't remarkably high...I've read the rules carefully and I don't recall seeing any mention of a minimum valve weight---which means that a designer can go crazy and make the valve ultra light---I say they just 'got too greedy'.

[Mirek]

Jan, it might sound weird but I am sure that the problems with broken valve springs on S2000 cars were real and not that uncommon.

On the other hand I think that only few times Fabia (the car with the longest stroke - 92 mm) suffered from broken conrod and that was due to a faulty batch of them. Otherwise even with brutal overrewing usually something else broke.

The long stroke actually doesn't apply to 1.6 WRC engines built from scratch (usually bore/stroke around 83/73). The only 1.6 WRC engine with long stroke was Mini due to the fact that it was the only one based on production unit (PSA/BMW EP6CDT).

[dimviii]

a reason for broken valves can be also from ''soft'' valve springs.
They try to use soft springs for less losses .How soft you can go is a compromise between less losses and precision valve drive at high rpms.
Soft valve springs (softer than ideal I would say) drives to valve float at high rpms,and that's can be dangerous for engine durability.
Of course the reason can be also and a bad quality batch of valve springs.

[J_n_z]

I may be wrong, but in term of absolute numbers, wrc engines don't seem too high tech to me. F1 Honda '88 engine with same 2,5 bar boost reved to more than 12000... I know F1 is not relly, but it was 30y ago.

I can imagine that it is tricky to achieve optimal effect with limited amount of air (optimal combustion), but it should not be problem to make it mechanicly reliable...

[Tarmop]

That 88 Honda F1 was a VERY different engine, much bigger. We are talking about a 1600cm3 R4 and imho it`s quite impressive, where we are today (not only WRC, but also small cm3 turbo engines on std. road cars but still we can see more reliability issues, like small TSI engines for example).

[J_n_z]

Bigger? OK, it was V6 but still 1500ccm...

[Mirek]

Bigger? OK, it was V6 but still 1500ccm...

Yes, F1 is different, rules, materials, area of use, fuel, the engine had only 50 mm stroke (closer to motorbikes of today than to cars). The point is that it is better not to use high rews when You don't need to do so. High rews mean also high friction losses (they grow with the square of engine speed) and therefore less efficiency (not only engine but also gearbox).


but also small cm3 turbo engines on std. road cars but still we can see more reliability issues, like small TSI engines for example).

In this case it's mostly about design flaws. It's possible to design totally reliable small turbo engine for decent price, the best example is 1.0T Ford EcoBoost

[janvanvurpa]

Jan, it might sound weird but I am sure that the problems with broken valve springs on S2000 cars were real and not that uncommon.

On the other hand I think that only few times Fabia (the car with the longest stroke - 92 mm) suffered from broken conrod and that was due to a faulty batch of them. Otherwise even with brutal overrewing usually something else broke.

The long stroke actually doesn't apply to 1.6 WRC engines built from scratch (usually bore/stroke around 83/73). The only 1.6 WRC engine with long stroke was Mini due to the fact that it was the only one based on production unit (PSA/BMW EP6CDT).

That makes sense on the "custom" engines...there IS a need for enough room to have valves of a certain size.....
The valve spring failures well that sound just plain wrong calculations and what I call "getting greedy design/choice wise.

I wonder how many guys here actually build and modify motors for competition???

[itix]

I'm sorry, my English is probably not good enough, but I don't know what You mean by valveflow.

Anyway I don't know the exact WRC rules.

AFAIK the problem with S2000 valves was that they had to be made of steel, i.e. they were heavy. With such high engine speed the valve springs had to cope with very high valve inertia. For me it is an example of a wrong idea how to make things cheaper.

Dim: That's exactly what I though - if the higher top speed as the only clear benefit is worth the effort to make the engine reliable at so high rpm. Maybe they simply set the limiter to lower value than what is allowed by the rules.
Sulland meant valve float I am quite sure. It is when the valve springs are not strong enough to close the valve properly given engine speed, boost pressure and cam profile, meaning that the valve and lifter is "floating" above the cam leading to a very abrupt close and valve failure.

[Mirek]

Thanks, I didn't know the English term.

[Fast Eddie WRC]

Quick one on aero and gearing...

I heard that on a long road in Monte there was a 10kph max speed difference between the new cars (202-212kph).

The Fiesta was fastest, then i20 and Yaris was slowest. Will this be mostly gearing or aero, or some of both ?

[KKS]

That story about when engine works on limiter, that always about gearing. No?

[Munkvy]

You could hear them on the rev limiter in some videos from Monte, that is definitely rev limiter. Aero should just effect how fast you get to the rev limiter based on drag. But that's just one element, there is also all the usuals like grip, torque, gear ratios and bravery...

[Lundefaret]

That story about when engine works on limiter, that always about gearing. No?

Its a combination of gearing and revs (on what rpm the rev limiter is set).

[Fast Eddie WRC]

Reports were that the Yaris had lower gearing hence hitting the rev-limiter earler than the other cars.

[N.O.T]

Reports were that the Yaris had lower gearing hence hitting the rev-limiter earler than the other cars.

making basic thoughts inside your head are not reports.

[KKS]

Its a combination of gearing and revs (on what rpm the rev limiter is set).
Of course yes. But limiter always set to high as possible revs. So if Toyota limiter is in low revs as other than they must use longer gears (final drive) as others.


are not reports.
This was announced by Colin Clark in his video yesterday. But this problem we see since Monte.

[Mirek]

Of course yes. But limiter always set to high as possible revs. So if Toyota limiter is in low revs as other than they must use longer gears (final drive) as others.

Not necessarily. It was stated here that 2017 RPM limit is 8500 rpm. It is quite possible that the teams don't use so high rpm. From power point of view there is no need for such high RPM due to the restrictor size and the only benefit is the higher top speed. It may not be worth of additional issues with tuning the engine for way higher RPM.

[Fast Eddie WRC]

Isn't the Fiesta's higher top speed (per Monte speed gun) likely to give an even more significant advantage on the faster events ? And considering it was competitive in Monte which isnt fast, it may have the best overall combination (power/aero/gearing) ?

[Mirek]

Higher top speed isn't always an advantage. You have to find the optimal balance between various quantities - acceleration, downforce and top speed. Add to that all the cars have different engine performance characteristics and You get a very very difficult situation for outside observer. IMHO it's near impossible to say if seeing some car having slightly higher top speed means also that the car had some advantage in the event.

And by the way they can (and likely will) use different gearing for other events.

[NickRally]

I posted the question below in the Rally Sweden thread thinking anybody present at the rally is more likely to be reading it and consequently come up with some images, but there haven't been any takers so far, so I will now post it here where it naturally belongs:


Any chance from anybody attending a WRC rally this year for few snapshots of the 2017 WRC cars diffusers from underneath, i.e. the transition area from the flat floor into the expansion volume? I assume this should be fairly easily done (so he said) with the cars on stands in the service park or when being unloaded from the transporters.
Many thanks,
Nick

[dimviii]

don't know if this one helps you.
https://pbs.twimg.com/media/C4Om5LfWEAAgn6M.jpg

[NickRally]

Not a bad shot at all, thanks dimviii.

It will be interesting to compare this to the other cars - from the outside the Fiesta appears to have the least aggressive diffuser, but until you see all the details, you never know.

[J_n_z]

https://mobile.twitter.com/TuomasToyry/status/827180112298774529
Not best quality but, that is what we have for now...

[NickRally]

Thanks J_n_z, please keep these coming.

[Fast Eddie WRC]

Sweden SS6: OSTBERG
Feeling the lack of rear aero. "It's horrible without the rear wing. The car is designed to have it... and without it it's the worst handing car."

No shit. ;)

http://img.photobucket.com/albums/v282/EddieFocus/mads_zps5ursbhhf.jpg

[N.O.T]

I think that aero is just a gimmick, after all there are many people who won stages without aero in the past...

[OldF]

I post this here also, easier to find than in the Sweden thread.

Latvala presents the Yaris’s aero. Nothing special what he says else that they have to have downforce also in the front because of big rear wing. In the end good view of the diffuser. They are not using the openings at front of the rear wheels in Sweden.

http://yle.fi/urheilu/3-9453531

[J_n_z]

I think that aero is just a gimmick, after all there are many people who won stages without aero in the past...

When 1995?

Man please keep of this thread, it is about how things work and not about how things are being said.
Look swedish rally results and stop making fool of yourself...

I am not following this sw rally closely, how rough are stages or are stages becoming?
It was said in the past that Toyota may have less suspension travel... if it is truth it should be working even better.

[N.O.T]

When 1995?

Man please keep of this thread, it is about how things work and not about how things are being said.
Look swedish rally results and stop making fool of yourself...

I am not following this sw rally closely, how rough are stages or are stages becoming?
It was said in the past that Toyota may have less suspension travel... if it is truth it should be working even better.

you must be new here kid...

[Fast Eddie WRC]

Craig Breen SS7 "The first time I've felt the effects of a damaged front aero package. We patched it up as best we could but it's incredible the effect that the aero makes..."

But NOT thinks he knows better... :rolleyes:

[Fast Eddie WRC]

According to Ogier, this is the rally where we’ll get to see the cars’ bigger wings influencing the proceedings for the first time.

"It’s always a compromise between finding some grip but also not having too much drag," he says. “With the speeds we’re going to have this weekend, aerodynamics is going to play a big role. You’ve also got some big straights here and drag is going to cost you speed and performance.

“I don’t know exactly how each team has worked on that, but it’s always a compromise between finding some grip but also not having too much drag. Here, the drag will have a big influence, especially on Knon. It’s really fast and has got long, long straights, so the engine is going to count, and aero as well.”

[janvanvurpa]

https://mobile.twitter.com/TuomasToyry/status/827180112298774529
Not best quality but, that is what we have for now...

Hej, is this you?


–

Tuomas Töyry

Finnish photographer and Rally Co-driver!Finland , Jämsä

·
tuomastoyryralli.kuvat.fi (http://t.co/QyEvP4kpoq)



–

[J_n_z]

@janvanvurpa

If you meant me... no, just saw pictures and posted the link. I have no access to live WRC at the moment, too much work to do and to many children to feed... some day, when my beard will be completely gray :)

[mozesii]

you must be new here kid...
You must be the dinosaur

[N.O.T]

You must be the dinosaur

i have built this place kid.

[mozesii]

i have built this place kid.
My point exactly dinosaur

[KKS]

What Nicolas are do at 26:00 here https://www.facebook.com/vincent.verstraete.18/videos/10210549309801771/ ?
Some stickers to radiator? But why?

[dimviii]

What Nicolas are do at 26:00 here https://www.facebook.com/vincent.verstraete.18/videos/10210549309801771/ ?
Some stickers to radiator? But why?

at very cold climate are blocking some air to the coolers(air/water) to help the engine work at normal temps.
All wrc cars at Sweden have some kind of these.

[skarderud]

Just a thought.
With the extended Aero, and in this specific, the flat floor and diffusor, will work better the closer to the ground it is. Are off's like meekes today be a result of gambling with rideheight? It was some real weird car-behaveior in the last corners egen you see the inboard from the insident.

Sent fra min XP7700 via Tapatalk

[stefanvv]

Just a thought.
With the extended Aero, and in this specific, the flat floor and diffusor, will work better the closer to the ground it is. Are off's like meekes today be a result of gambling with rideheight? It was some real weird car-behaveior in the last corners egen you see the inboard from the insident.

I think he was just too fast there, the car didn't turn. But in theory, yes, the low pressure area beneath the car is weaker with bigger ride height.

[KKS]

at very cold climate are blocking some air to the coolers(air/water) to help the engine work at normal temps.
All wrc cars at Sweden have some kind of these.
They do this after/before each stage? For road/stage mode?

[dimviii]

I ve seen it at stage mode.Probably is up to what temperatures they have.

[NickRally]

Here is my first attempt at creating an aero analysis of the 2017 WRC cars. There is always a risk of making oneself look like a fool when doing this, but I’ll give it a go :). I will start with the Fiesta and will expand with all the other cars as and when I have the time, but I can already see some very interesting features on the Yaris. I am also no expert on the regulations and although I have downloaded them, the nature in which they are presented is very different to the world of ground up designed racing cars where I come from, which makes the WRC tech regs a real challenge for me to follow.

1. Ford Fiesta

1235

The diffuser on the Fiesta appears to be the shallowest (1) of them all, this is not necessarily a disadvantage in terms of aero, but it is quite modest in comparison to the rest of the field. The transition area into the diffuser (2) is quite narrow as dictated by the suspension arm protectors (3), which in turn, at their trailing edge, do not form a continuous transition into the diffuser, though they probably provide a nice skirted area around the central floor into the diffuser transition, which would help with accelerating the air flow and reducing the air pressure further there. Nevertheless, integrating the trailing edges nicely into the diffuser surface (notwithstanding the technical challenges involved in this) may deliver an added benefit (something that appears to be done on the Yaris on some of the images). The diffuser streaks appear to extend below the surface of the flat floor in front of the diffuser, but I suspect this is optical illusion and like in many other forms of mototsport they are not allowed to do so, but once again a proper read of the tech regs should provide an answer to this question.
Moving towards the front of the car, there appears to be a non-flat area, which I don’t know if it is because of the tech regs/homologation or it is done for creating an aero benefit. The image is not clear enough for me to see what happens there, but I can see similar features on the Yaris, though on some of the images of the Toyota from testing, I can also clearly see additional diffusers in front of the rear wheels, though more on this later.

Regards,
Nick

[J_n_z]

We have a month of speculation ahead :) but let me to start a technical discussion (not a statistic and history analysis)...

Monte and Sweden are classified as special rallys with no real performance indication.

If monte conidions are 2017 like reason is simple; there is never enough grip under tires so car can't perform at its "working ability".

In Sweden it is not so obvious to me. Special snow tires gives grip that can be compared with the one on gravel. Gravel roads under the snow are diverse, from fast and flowing to narrow, "cresty", camber changing and even rough. If there are big snowbanks driving style can be different, otherwise driving is quite similar to gravel. In the past when tires were super narrow and rims were bigger, tire dynamic may be different, but with 15" rims I can imagine that tires perform similar to gravel ones. So I can't find a obvious reason why fast snow car would not be a also a fast gravel car. (again not talking about drivers, used to snow or not and snowbanks leaning driving)

Let me hear your opinion...

[mozesii]

Here is my first attempt at creating an aero analysis of the 2017 WRC cars. There is always a risk of making oneself look like a fool when doing this, but I’ll give it a go :). I will start with the Fiesta and will expand with all the other cars as and when I have the time, but I can already see some very interesting features on the Yaris. I am also no expert on the regulations and although I have downloaded them, the nature in which they are presented is very different to the world of ground up designed racing cars where I come from, which makes the WRC tech regs a real challenge for me to follow.

1. Ford Fiesta

1235

The diffuser on the Fiesta appears to be the shallowest (1) of them all, this is not necessarily a disadvantage in terms of aero, but it is quite modest in comparison to the rest of the field. The transition area into the diffuser (2) is quite narrow as dictated by the suspension arm protectors (3), which in turn, at their trailing edge, do not form a continuous transition into the diffuser, though they probably provide a nice skirted area around the central floor into the diffuser transition, which would help with accelerating the air flow and reducing the air pressure further there. Nevertheless, integrating the trailing edges nicely into the diffuser surface (notwithstanding the technical challenges involved in this) may deliver an added benefit (something that appears to be done on the Yaris on some of the images). The diffuser streaks appear to extend below the surface of the flat floor in front of the diffuser, but I suspect this is optical illusion and like in many other forms of mototsport they are not allowed to do so, but once again a proper read of the tech regs should provide an answer to this question.
Moving towards the front of the car, there appears to be a non-flat area, which I don’t know if it is because of the tech regs/homologation or it is done for creating an aero benefit. The image is not clear enough for me to see what happens there, but I can see similar features on the Yaris, though on some of the images of the Toyota from testing, I can also clearly see additional diffusers in front of the rear wheels, though more on this later.

Regards,
Nick

Pse keep em coming

[NickRally]

I post this here also, easier to find than in the Sweden thread.

Latvala presents the Yaris’s aero. Nothing special what he says else that they have to have downforce also in the front because of big rear wing. In the end good view of the diffuser. They are not using the openings at front of the rear wheels in Sweden.

http://yle.fi/urheilu/3-9453531

Thanks OldF, but I can't view it, restriction on being viewed from outside Finland.
Regards,
Nick

[NickRally]

Couple of other thoughts after my first post on aero:

1. Double diffuser on the Ford – it was mentioned on this forum and also such thought crossed my mind when I first saw the Fiesta small diffuser at the launch. I thought there was no way that was all the diffuser they have designed in and it also appeared like the original road car “diffuser” on top is used as an additional extraction device, though it wasn’t clear where on the underfloor this particular air would have been taken from, even though there are plenty of openings on the underside as it would appear. Nevertheless looking at images a bit later on, I couldn’t see an air passage between the dedicated WRC diffuser and the road car one so I discarded that thought, but once again none of the images I have seen so far is clear enough to say for certain what’s what and I haven’t seen one in person. Maybe people that have seen the real car with their own eyes can comment?

2. The technical analysis thread itself – there are a lot of sub-threads in it and it feels very fragmented and inconsistent, jumping from one subject to another. I understand why this is, as until recently rally car technical analysis wasn’t a massive subject with little year on year car development (relative to other forms of motorsport) so a single technical thread was enough. But now with the new cars there is a lot that can be said, so there may be justification to split the technical analysis thread into individual threads dealing with engine, mechanical chassis, aero chassis, on stage performance and so on. On the other hand I can of course see an argument for the opposite with technical threads appearing on all sorts of subject and ending up with many, clogging the forum. So not sure what the best compromise is, just pondering ideas. If people are happy to keep just the single thread in existence, I am sure I would be able to “deal” with it :).

Regards,
Nick

[OldF]

Thanks OldF, but I can't view it, restriction on being viewed from outside Finland.
Regards,
Nick

I was afraid that could be the case. I made few “print screens” of the diffuser from the video. Hope it helps.

http://i267.photobucket.com/albums/ii284/OkdF/Toyota%20diffuser%201_zpsyewl16ch.jpg

http://i267.photobucket.com/albums/ii284/OkdF/Toyota%20diffuser%202_zpsukaxi7pt.jpg

http://i267.photobucket.com/albums/ii284/OkdF/Toyota%20diffuser%203_zpsqchxbaoc.jpg

[J_n_z]

Compare 1:31 and 2:46
https://www.youtube.com/watch?v=nImA9omDSrQ&app=desktop

put it in slow motion to see better and look front wheels.

Is it suspension settings or downforce? I have felling that sunday was actually first time Latvala was pushing 100 %, before that he was driving at "sensible 98 %" avoiding stupidities.

[dimviii]

Compare 1:31 and 2:46
https://www.youtube.com/watch?v=nImA9omDSrQ&app=desktop

put it in slow motion to see better and look front wheels.

Is it suspension settings or downforce?.
I d like to see a video from this point from previous years,(if the stage run at 2016)

[NickRally]

Compare 1:31 and 2:46
https://www.youtube.com/watch?v=nImA9omDSrQ&app=desktop

put it in slow motion to see better and look front wheels.

Is it suspension settings or downforce? I have felling that sunday was actually first time Latvala was pushing 100 %, before that he was driving at "sensible 98 %" avoiding stupidities.

I tend to agree with J_n_z on both points.
The Fiesta and the Yaris differ in the way they negotiate this piece of road and I won't be surprised at all if it is due to the downforce levels difference between the two cars rather than the suspension settings, especially at these speeds.
And second, it certainly feels like Latvala finally showed what they can do together with the car on the final day.

[NickRally]

Here is the next instalment of my aero analysis, this time it is Yaris’ turn.

2. Toyota Yaris

I will first upload the images, which in many instances are self-explanatory and will follow with the comments later, once again as and when I find the time.

Regards,
Nick

1237

1238

1239

1240

1241

[jparker]

Quick question. Is it optical illusion, or the pedals have gone upwards, almost lining up with the driver's seat? Is this regulated, or is just driver's preference?

[Marcco]

Couple of other thoughts after my first post on aero:

1. Double diffuser on the Ford – it was mentioned on this forum and also such thought crossed my mind when I first saw the Fiesta small diffuser at the launch. I thought there was no way that was all the diffuser they have designed in and it also appeared like the original road car “diffuser” on top is used as an additional extraction device, though it wasn’t clear where on the underfloor this particular air would have been taken from, even though there are plenty of openings on the underside as it would appear. Nevertheless looking at images a bit later on, I couldn’t see an air passage between the dedicated WRC diffuser and the road car one so I discarded that thought, but once again none of the images I have seen so far is clear enough to say for certain what’s what and I haven’t seen one in person. Maybe people that have seen the real car with their own eyes can comment?

Regarding double diffuser. I don't really think it is double. I was reading this book about aeordynamics (by Simon McBeath) and CFD analysis shows that efficient angle of diffuser is somewhere between 8-12 degrees. Now 8 degrees is quite shallow, any road car has this angle. And, as I understand primary function of diffuser is to balance downforce between front and rear (same as rake). So in Fiesta case it could be that front-end has enough downforce thus large difusser angle is not needed.

[NickRally]

Hi Marcco, the 8-10deg diffuser angle quoted was applicable to the flat bottom formula cars of the early 90's and it changed (the optimal angle got bigger) with the change in the rules specifying stepped floors for the F1 cars (that's pretty much what I do for living). As a general rule of thumb, the higher the distance between the floor of the car and the road, the higher the optimal diffuser angle. Also if we accept the theory that the diffuser will add equal amounts of downforce to both axles of the car (which probably wouldn't be the case with a bit more going to the rear being more probable), then higher diffuser angle than the one on the Fiesta would look more appropriate.
Regarding the double diffuser, the only way it won't be doable is if the rules do not allow it (for one reason or another), otherwise there is no stopping the creativity of the designers.
Regards,
Nick

[J_n_z]

... the rules specifying stepped floors for the F1 cars (that's pretty much what I do for living). ...
Nick
I like this...

@ Yaris: You didn't mentioned Yaris "nose up" floor design.
Look:

https://www.google.si/imgres?imgurl=http%3A%2F%2Fperformancedrive.com.au %2Fwp-content%2Fuploads%2F2017%2F01%2FToyota-Yaris-WRC-at-2017-Rallye-Monte-Carlo.jpg&imgrefurl=http%3A%2F%2Fperformancedrive.com.au%2Ft oyota-off-great-start-2017-wrc-2nd-rallye-monte-carlo-2322%2F&docid=A6f4jJHgqh_B1M&tbnid=M06JN_yHhGnDlM%3A&vet=1&w=1280&h=830&client=ubuntu&bih=854&biw=1652&q=yaris%20wrc%20monte%20carlo&ved=0ahUKEwiam5zpqJbSAhVMlCwKHe5NDWUQMwgcKAQwBA&iact=mrc&uact=8#h=830&imgrc=M06JN_yHhGnDlM:&vet=1&w=1280
https://www.google.si/imgres?imgurl=http%3A%2F%2Fperformancedrive.com.au %2Fwp-content%2Fuploads%2F2017%2F01%2FToyota-Yaris-WRC-at-2017-Rallye-Monte-Carlo.jpg&imgrefurl=http%3A%2F%2Fperformancedrive.com.au%2Ft oyota-off-great-start-2017-wrc-2nd-rallye-monte-carlo-2322%2F&docid=A6f4jJHgqh_B1M&tbnid=M06JN_yHhGnDlM%3A&vet=1&w=1280&h=830&client=ubuntu&bih=854&biw=1652&q=yaris%20wrc%20monte%20carlo&ved=0ahUKEwiam5zpqJbSAhVMlCwKHe5NDWUQMwgcKAQwBA&iact=mrc&uact=8#h=830&imgrc=M06JN_yHhGnDlM:&vet=1&w=1280
https://www.google.si/imgres?imgurl=https%3A%2F%2Fi.ytimg.com%2Fvi%2FAqP 9VlHFW5Q%2Fsddefault.jpg&imgrefurl=https%3A%2F%2Fracingfail.com%2Ftoyota-yaris-wrc-2017-new-tarmac-test-with-tommi-makinen-by-jaume-soler%2F&docid=y9FoccYE4jqGnM&tbnid=54gEFv6hdqtqlM%3A&vet=1&w=640&h=480&client=ubuntu&bih=854&biw=1652&q=yaris%20wrc%20tarmac&ved=0ahUKEwjVr6LKqJbSAhWBliwKHbflAAMQMwgmKA4wDg&iact=mrc&uact=8#h=480&imgrc=54gEFv6hdqtqlM:&vet=1&w=640
http://cdn-9.motorsport.com/images/mgl/6gnrWonY/s8/wrc-rally-sweden-2017-jari-matti-latvala-miikka-anttila-toyota-yaris-wrc-toyota-racing.jpg
https://www.google.si/imgres?imgurl=http%3A%2F%2Fs3-eu-west-1.amazonaws.com%2Fcarmag-wp%2Fcarmag%2Fwp-content%2Fuploads%2F2016%2F12%2F21123149%2Fyaris-wrc1-790x474.jpg&imgrefurl=http%3A%2F%2Fwww.carmag.co.za%2Fspeed_po st%2Ftoyota-yaris-wrc-is-angry-and-ready-for-action%2F&docid=D5EUswgJiPSa3M&tbnid=kIFoj0xXGLyt5M%3A&vet=1&w=790&h=474&client=ubuntu&bih=854&biw=1652&q=yaris%20wrc&ved=0ahUKEwjqm8SKqJbSAhUElCwKHfPUD6c4ZBAzCCwoKDAo&iact=mrc&uact=8#h=474&imgrc=kIFoj0xXGLyt5M:&vet=1&w=790

It looks like it is purposefully made to receive air under the floor... ground effect in mind.

I see the "side skirts" diffusers looks like a clever trick, but I don't understand why the front part of the skirts is cut away, is there aerodynamic purpose or a mechanic (rocks flying) one.

@ general underfloor aero: I think, we can not be sure that floor generated downforce is a vital part of car performance. Hyundai rear suspension cover were floating massively. As far as I can understand this should kill all floor aero performance.
https://www.youtube.com/watch?v=gwyGvSPtgJ8 (0:41 to 0:47)

[A FONDO]

For the guy who wanted the bottom of the car

http://www.ewrc.cz/ewrc/image_browse.php?id=339519

also can be seen the destroyed aero before the rear tyre, wonder how it happened

[SubaruNorway]

Anyone know what the black boxes at the top of the fenders where the bumper is attached is?
http://www.ewrc-results.com/image.php?id=339629&entry=0&car=0

[jparker]

Good video for tech analysis:
https://youtu.be/RfTeBPXkTps

[NickRally]

Before I have forgotten again:

mozesii - thanks for the appreciation.

OldF - great images, thanks, as you would have already seen, I have put them to good use.

SlowSon - thanks, good photo.

jparker - thanks, I will have a look.

J_n_z - thanks.
On a crcuit racer the answer to the question you asked without a doubt would be yes to a raised centre section of a front splitter. On a rally car with its higher ground clearance the effect will be less pronounced, but I suppose (short of this being done to simply increase the ground clearance in the middle of the vehicle to go over road obstacles) it can still help.
The side tunnels on the Yaris - if I was doing it, then my reasoning for moving the leading edge rearward would be to ensure that the tunnels get a slightly cleaner air away from the front wheels and in general increase the mass flow of air to them rather than being shadowed by the front wheels too much.
The importance of aero on a rally car - you are most likely correct about the Hyundai's flapping suspension guards, but that is why I like the rally cars, aero is not king (in massive difference to F1), the mechanical side is of utmost importance. At the same time, with the new rules, aero becomes more and more important without overshadowing the other engineering sides and whoever gets to do the best job on all design fronts will end up with the fastest car overall.

Regards,
Nick

[Ctesibios]

Here is my first attempt at creating an aero analysis of the 2017 WRC cars. There is always a risk of making oneself look like a fool when doing this, but I’ll give it a go :). I will start with the Fiesta and will expand with all the other cars as and when I have the time, but I can already see some very interesting features on the Yaris. I am also no expert on the regulations and although I have downloaded them, the nature in which they are presented is very different to the world of ground up designed racing cars where I come from, which makes the WRC tech regs a real challenge for me to follow.

1. Ford Fiesta

1235

The diffuser on the Fiesta appears to be the shallowest (1) of them all, this is not necessarily a disadvantage in terms of aero, but it is quite modest in comparison to the rest of the field. The transition area into the diffuser (2) is quite narrow as dictated by the suspension arm protectors (3), which in turn, at their trailing edge, do not form a continuous transition into the diffuser, though they probably provide a nice skirted area around the central floor into the diffuser transition, which would help with accelerating the air flow and reducing the air pressure further there. Nevertheless, integrating the trailing edges nicely into the diffuser surface (notwithstanding the technical challenges involved in this) may deliver an added benefit (something that appears to be done on the Yaris on some of the images). The diffuser streaks appear to extend below the surface of the flat floor in front of the diffuser, but I suspect this is optical illusion and like in many other forms of mototsport they are not allowed to do so, but once again a proper read of the tech regs should provide an answer to this question.
Moving towards the front of the car, there appears to be a non-flat area, which I don’t know if it is because of the tech regs/homologation or it is done for creating an aero benefit. The image is not clear enough for me to see what happens there, but I can see similar features on the Yaris, though on some of the images of the Toyota from testing, I can also clearly see additional diffusers in front of the rear wheels, though more on this later.

Regards,
Nick
Thanks for doing a serious aero analysis a la Mulsanne's Corner.

It's interesting to see all the different solutions being tried by the teams because of the current freedom in the rules!

[Ctesibios]

Hi Marcco, the 8-10deg diffuser angle quoted was applicable to the flat bottom formula cars of the early 90's and it changed (the optimal angle got bigger) with the change in the rules specifying stepped floors for the F1 cars (that's pretty much what I do for living). As a general rule of thumb, the higher the distance between the floor of the car and the road, the higher the optimal diffuser angle. Also if we accept the theory that the diffuser will add equal amounts of downforce to both axles of the car (which probably wouldn't be the case with a bit more going to the rear being more probable), then higher diffuser angle than the one on the Fiesta would look more appropriate.
Regarding the double diffuser, the only way it won't be doable is if the rules do not allow it (for one reason or another), otherwise there is no stopping the creativity of the designers.
Regards,
Nick
I had mentioned the double diffuser in another thread. It's hard to validate, but if they are using it as such, the air has to come from somewhere? The M-Sport diffuser is very shallow compared to the others. Could it be as or more efficient than the others? Time will tell, we will see who copies who! As a matter of fact, are aero changes allowed during the season or is everything pretty much homologated for the whole season?

[NickRally]

Good video for tech analysis:
https://youtu.be/RfTeBPXkTps

Thanks again jparker, it is amusing to see how it never occurs to them to point the camera to the underside, which is where a lot of the interesting aero stuff takes place. Of course this is understandable considering that floors so far have not been massive differentiator in performance, but with the new rules, who knows. Funnily though, the Hyundai (the car in the video) has one of the roughest undersides if some of the distant images I have seen are anything to go by.

[NickRally]

Thanks for doing a serious aero analysis a la Mulsanne's Corner.

It's interesting to see all the different solutions being tried by the teams because of the current freedom in the rules!

Thanks Ctesibios.

Regarding the efficiency of the Fiesta diffuser, I suppose it depends how you measure efficiency - if it is lift to drag ratio in isolation, then it might be, but if we measure efficiency as overall car lift to drag ratio, then at least to me it doesn't appear very efficient, but of course I haven't seen the numbers from their aero analysis. As you say time will tell who got it right.

Your question about allowed aero development through the year, I would be interested in the answer to this as well, though my suspicion and fear is that it will be close to none.

My personal preference of course would have been for much more freedom, but we all know how modern motorsport goes. Having said that, I think world rallying itself will benefit from a bit more aero (and other technical) development freedom as it will make people talk more about it, the past winter is a good example for this. You basically need to generate constant buzz around given subject if you wish people to pay interest to it on a more permanent basis.

[NickRally]

Guys,
After studying the 2017 WRC tech rules in more detail, there is one recurring theme, the reference to an additional document called homologation extension form 400/01 WRC, which either is not on FIA’s site or I am not skilful enough to find it. Is there anybody able to point me in the right direction for it, or is maybe already in possession of this form and is willing to share it?
Thanks,
Nick

[Mirek]

Hello Nick, normally the homologation extensions are not public. Maybe it is possible to ask them directly from FIA, I don't know, but for sure You can't find them on the internet (for any classes). I had them only once in my hand but those were initial ones for S2000 cars which means it's already eleven years old document.

[NickRally]

Thanks Mirek, to ask more specifically, let's take the diffuser rules - there is nothing in the tech regs saying what these are other than the reference to the homologation extension form 400/01 WRC, so for people like me coming from the world of circuit racing, it is unclear how the teams go about designing the diffusers if there is not a single point of tech reference that is the same for everyone. I appreciate all the base cars are different, but surely they all must be given some constraints, like how far back it can extend for example - where are these published?

[Mirek]

These details are probably part of the document we discussed before. Sadly it's not publicly available on the FIA website. I think that Your local ASN shall be able to provide the document to You. Maybe it's not for free. I really don't know as I have never tried to obtain one (the one I have I got for some work I did long time a go).

[NickRally]

I see, thanks Mirek, might be worth giving this a go.

[Mirek]

Send me PM if You are interested in the old homologation regulations for S2000 cars to see if it's what You're searching for.

[danon]

https://www.graphicnews.com/links/gn_swf/swf-34500-34999/GN34982R_EN/GN34982-Artboard_1.png

[EightGear]

At least now we know Lefebvre is Estonian.

[pantealex]

At least now we know Lefebvre is Estonian.

also Breen and Lappi are not team drivers, but Evans is.

[J_n_z]

If these pics. are to believe, Fiesta is technicaly the shortest car, to my surprise, I was sure Yaris is the smallest.

[GravelBen]

If these pics. are to believe, Fiesta is technicaly the shortest car, to my surprise, I was sure Yaris is the smallest.

Shortest wheelbase at least, the Yaris overall length might still be shorter.

[jparker]

Pictures are also showing Citroen with longest wheelbase, but that should be the Hyundai, so the numbers look suspicious too.

[NickRally]

According to the official Hyundai Motorsport site, i20 is 2570mm wheelbase:

1254

I guess I need to run it through an image processing software and find out which one is correct.

[Munkvy]

Apparently Mads Ostberg did Sweden without the Centre diff mapped... According to https://www.motorsport.com/wrc/news/fia-eyes-motogp-style-team-structure-for-wrc-876831/

To quote - "I didn’t use the centre differential, we just locked it because we didn't have time to work out the settings." Which is interesting, wonder how much impact that had on the handling!

[NickRally]

Finally some time to write few lines on the Toyota images I uploaded earlier.
(1) The diffuser is shorter than the Fiesta, but I suspect this was in order to allow it to be more steeply raked inside the constraints placed by the road car package and regulation requirements. Part of this is the necessity to place the transition point (2) from the flat floor into the diffuser further back than the Fiesta. This arrangement will produce more suction at the transition point resulting in more downforce from the floor area. To an extent, people might be put off by higher diffuser angles as they will be more sensitive to ride height changes, but I genuinely can’t imagine this being a problem on the current rally cars (it would have been noticeable on the old flat bottom cars). Once again it would appear the lower edge of the diffuser strakes is touch below the flat floor ahead of the diffuser. Also note the small gap between the suspension guard and the floor with the shape of the guard having a nice curvature around the suspension opening – whether the gap is supposed to be there or shows detached guard, is not clear to me at this stage.
In (3) and (4) you can see the most interesting in my view feature on the Yaris, the side Venturi tunnels - I suppose they were made easier by the narrower road car width. I am not entirely clear (that is I am not clear until the technical document outlining these features becomes available) how much mods to the original bodyshell are permitted under the new rules in order to fit such tunnel, and so the question remains could a team like Citroen for example have fitted such tunnels in their design with the wider road car package. Nevertheless a nice feature on the Toyota and a well done to the designers, it reminds me of the early F1 ground effect cars of 1979-1980 with their separate (to the main tunnel) side Venturi tunnels placed ahead of the rear wheels and very steeply raked (you can check Ligier of this period for a good example of this).
In (5) you can see the flat underbody side panels on the Ford and the Citroen (Hyundai is similar). Once again it is yet to be established if the designers of the rival squads struggled to fit these and decided against them as not being very effective or simply did not think of employing such features.
On (6) there are some areas where the floor is not smooth/flat, which is not present on other photographs (i.e. they are closed off creating smooth floor) – not sure if this is packaging/ballast/weight/tuning tool or something to do with the aero platform. This appears to be happening (on/off panels) on all the cars.
On (7) you can see two examples of the rear suspension guards – on the left nicely attached and on the right detached from the floor – I suspect these guards will form a constant part of the faults meetings in the team post every rally :).
And on (8) below (additional photo), you can see the trimmed central part of the front splitter skirt as pointed out by J_n_z (thanks J_n_z) – I wasn’t sure how much effect this would have with the ride heights being run, but after pondering it, I suppose the skirt itself will have the effect of artificially reducing the effective ride height (i.e. the effective ride height that the air sees which will most likely be smaller than the actual skirt gap) and so by trimming it in the central portion, it acts in a similar manner to the raised front splitter on the sports prototype cars for example.

www.geocities.ws/rallytech/aero/toyota/Yaris%20Aero%207.JPG

One other interesting feature that might be present on the 2017 WRC cars could be some small Venturi tunnels/diffusers ahead of each front wheel, but I haven’t yet seen good photos proving or disproving their presence. I am also not entirely sure how effective they would be with the front splitter skirt present ahead of them. We will have to wait for some better photos there.

Regards,
Nick

[traxx]

https://pbs.twimg.com/media/C6R3kg-U4AEjz9X.jpg

Any idea why we can't see no pipe from the inlet in front of the rear wheel to the rear brakes ?
As we can see on the other cars...

[Oppositelock]

And on (8) below (additional photo), you can see the trimmed central part of the front splitter skirt as pointed out by J_n_z (thanks J_n_z) – I wasn’t sure how much effect this would have with the ride heights being run, but after pondering it, I suppose the skirt itself will have the effect of artificially reducing the effective ride height (i.e. the effective ride height that the air sees which will most likely be smaller than the actual skirt gap) and so by trimming it in the central portion, it acts in a similar manner to the raised front splitter on the sports prototype cars for example.

www.geocities.ws/rallytech/aero/toyota/Yaris%20Aero%207.JPG

One other interesting feature that might be present on the 2017 WRC cars could be some small Venturi tunnels/diffusers ahead of each front wheel, but I haven’t yet seen good photos proving or disproving their presence. I am also not entirely sure how effective they would be with the front splitter skirt present ahead of them. We will have to wait for some better photos there.

Regards,
Nick[/QUOTE]

Hi Nick,

great to read your analysis. But in one point I have to contradict (if this is the right word in English). My opinion: The middle part of the front splitter is simply higher off the ground because usually the middle of a normal road (other than a race track) is a little bit higher compared to where the wheels are placed on the road. So having the middle of the front splitter a little bit higher prevents the splitter from being damaged.

What do you think?

[NickRally]

Thanks Oppositelock, you could well be correct there - I seem to have my "aero hat" permanently on :), but it could simply have been done for basic road clearance reasons.

[NickRally]

https://pbs.twimg.com/media/C6R3kg-U4AEjz9X.jpg

Any idea why we can't see no pipe from the inlet in front of the rear wheel to the rear brakes ?
As we can see on the other cars...

Is the car in a fully built state regarding the brakes or are there more bits to go on as far as the brakes are concerned? I.e. I can't see one at the front either, but the angle is not great for this.

[traxx]

Here, we can see the pipes to lead fresh air to the rear brakes of other cars. It seems that Hyundai removes the sticker on the inlet which was there in MC and Sweden (low temps for these events)

https://pbs.twimg.com/media/C6VpHdgWYAEgYBj.jpg:large
https://pbs.twimg.com/media/C6YHXLuWcAAFboq.jpg
https://pbs.twimg.com/media/C6WQR7kVMAAkq70.jpg:large

[Mirek]

An interesting thing is that there are three channels in Ford - one presumably leading to the rear differential and two seem to lead to the brake but why two? Do they intend to increase effectiveness by sending the air on larger area of the disc or is it for some other reason (or cooling of different part)?

Also I haven't seen yet any photo of Yaris with hoses installed at the rear axle. Do they use them at all? Also the damper canister is at the frontal side of the strut i.e. possibly affecting the air flow coming to the brakes (not that it wouldn't enjoy some cooling).

It's also interesting that Hyundai has the air intakes so high under the windows. I guess that it must be to prevent dirt coming into the air channel.

[A FONDO]

Yes, there were pictures of C3 with that hole full of gravel before they put a net. Hyundai invented it much better.

[NickRally]

I wouldn’t be surprised if, of the two pipes on the Fiesta leading to the brake system, one is delivering air to the centre of the disc and the other to the calliper.

[jparker]

Also I haven't seen yet any photo of Yaris with hoses installed at the rear axle. Do they use them at all?
Is it possible the hose is traveling via the diff, and then outward, blowing perpendiculary?

[J_n_z]

Can someone tell something about different gravel tyre profiles, what is the difference...?

Here we can see one Michelin option https://pbs.twimg.com/media/C6WNfoCU4AAy7Su.jpg
Here is an other (as far as I know this one is more used) https://pbs.twimg.com/media/C6QdjXNVUAEnzjU.jpg

[dimviii]

Also I haven't seen yet any photo of Yaris with hoses installed at the rear axle. Do they use them at all? .

https://pbs.twimg.com/media/C6bXzqQVUAANGFL.jpg

[Mirek]

Can someone tell something about different gravel tyre profiles, what is the difference...?

Here we can see one Michelin option https://pbs.twimg.com/media/C6WNfoCU4AAy7Su.jpg
Here is an other (as far as I know this one is more used) https://pbs.twimg.com/media/C6QdjXNVUAEnzjU.jpg

I think that this year WRC and WRC2 tyres aren't same. The new cars with much more aero downforce and stronger engines need more durable tyres.

[Ctesibios]

Here, we can see the pipes to lead fresh air to the rear brakes of other cars. It seems that Hyundai removes the sticker on the inlet which was there in MC and Sweden (low temps for these events)

https://pbs.twimg.com/media/C6VpHdgWYAEgYBj.jpg:large
https://pbs.twimg.com/media/C6YHXLuWcAAFboq.jpg
https://pbs.twimg.com/media/C6WQR7kVMAAkq70.jpg:large
The trailing edge of the floor at the junction of the rear wheel arch on the Hyundai seems to have a diffuser like profile. Ie, the section of floor between the front and rear wheel arches ends with a curved profile at the rear. Possibly the Toyota also?

[AMSS]

What are the black tunnels on the Citroen leaving out from the rear boot to the bottom? Seems a bit extensive if it`s just cabin pressure removal, and if it was that than why lead them to the bottom?

[dimviii]

vents to rear diff probably,ds3 wrc had also too

[Mirek]

The trailing edge of the floor at the junction of the rear wheel arch on the Hyundai seems to have a diffuser like profile. Ie, the section of floor between the front and rear wheel arches ends with a curved profile at the rear. Possibly the Toyota also?

Yes, it looks like that

https://pbs.twimg.com/media/C6VNpnMUYAAlaaP.jpg

[kiil]

I wouldn’t be surprised if, of the two pipes on the Fiesta leading to the brake system, one is delivering air to the centre of the disc and the other to the calliper.

Exactly, saw this in Monte.

[Marcco]

It's also interesting that Hyundai has the air intakes so high under the windows. I guess that it must be to prevent dirt coming into the air channel.

I think it's because doors are too close and there are simply no space to put it anywhere else.

[NickRally]

Thanks kiil.

Ctesibios, on the Toyota this is the exit for the side Venturi tunnels ( www.geocities.ws/rallytech/aero/toyota/Yaris%20Aero%202.JPG ) unless of course they use some convoluted ducts to exit the air from the side Venturi tunnels through the grills behind the rear wheels.
On the Hyundai, they appear to have very small diffusers/curved sections at the trailing edge of the side horizontal doorsills/splitters as you pointed out.

[Sulland]

Sensors:
How many places in engine and other places does the 2017 cars have sensors giving data to teams and in the cars?
Are all sensordata being transmitted to team HQ, or only the most important data?

[makinen_fan]

The sensors (and their number if duplicated) that you can use in engine/centre diff strategies is controlled by FIA. Monitoring sensors are free.
If you mean telemetry, you are not allowed to transmit anything from car to service. Data exchange is only in media zones before service, in the form of usb/memory card.

[NickRally]

To add to the Toyota analysis and also to my musings on the possibility of there being small Venturi tunnels ahead of the front wheels, well the image of the Yaris below shows there are no such tunnels there. Will keep an eye for good images of the other cars to see the arrangements in this area, though I suspect very unlikely for any of them to have these.

http://www.geocities.ws/rallytech/aero/toyota/Yaris%208.htm

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[sonnybobiche]

Can we talk about the complex, downforce-generating wing mirrors that the Yaris debuted with, which very late in testing actually disappeared from the car altogether, and which eventually came back as the simplified single-plane ones that actually got homologated?

I read a translated finnish interview with Makkinen where it was clear he was angry about having to deal with last-minute changes to the aero regulations. Anyone want to bet one or another team saw the wing mirrors, got super envious, and filed a 'request for clarification' with the FIA?

[Mirek]

I don't think that the mirrors make so much difference.

[mozesii]

Does anyone have pictures of Toyota's rear suspension for Sweden/Monte and Mexico? I ask because a 1.5cm reduction on the rear, will greatly affect chassis agility, maneuverabilty and especially high speed stability.

[NickRally]

Can we talk about the complex, downforce-generating wing mirrors that the Yaris debuted with, which very late in testing actually disappeared from the car altogether, and which eventually came back as the simplified single-plane ones that actually got homologated?

I read a translated finnish interview with Makkinen where it was clear he was angry about having to deal with last-minute changes to the aero regulations. Anyone want to bet one or another team saw the wing mirrors, got super envious, and filed a 'request for clarification' with the FIA?

It is not easy to talk about the wing mirror stays when we don’t know the specific tech rules regarding aero (remember form 400/01 WRC), which means the changes could have been provoked by having to comply with some initially grey area in the rules, which was then clarified or they could have come about as a result of evolution in the aero concept of the complete car, i.e. changes to the rear wing might have come as a package deal together with the mirror stays for example.

[NickRally]

Also wondering if anybody has any insight into the downforce figures the 2017 WRC cars produce (or has this already been discussed?) – I know this will be a well-guarded secret, but wondering if anybody has heard anything in conversation.
If I was to make a very wild guess on the numbers (which could be way way off the mark), I would maybe say 200kg (+/-50kg) at 150kph in tarmac trim, which would roughly equate to the downforce produced by the special track editions of the “hyper” cars and slightly above than that of the road versions of these cars. This number will also be slightly below what a Formula 3 car produces. Then of course we can expand the question to what the downforce numbers are in gravel spec :)

[Sulland]

Does anyone have pictures of Toyota's rear suspension for Sweden/Monte and Mexico? I ask because a 1.5cm reduction on the rear, will greatly affect chassis agility, maneuverabilty and especially high speed stability.

Why do they have to loose 1,5 cm travel on the rear?

[KiwiWRCfan]

Why do they have to loose 1,5 cm travel on the rear?
At Monte Carlo it was found car did not meet regulation requirements. It was considered no competitive advantage was gained and TGR were given until Mexico to correct the error without penalty

[Mirek]

In other words they let them drive only because it was the first event for the new cars. Normally it's very clear disqualification.

[mozesii]

There is competitive advantage. Probably could explain the constant TGR mention of trying out different setups.

[N.O.T]

Another indication how much of an amateur team they are in their current format.

[Sulland]

At Monte Carlo it was found car did not meet regulation requirements. It was considered no competitive advantage was gained and TGR were given until Mexico to correct the error without penalty

Is max suspesiontravel specified in the regulations? If yes, why?

[Rally Power]

At Monte Carlo it was found car did not meet regulation requirements. It was considered no competitive advantage was gained and TGR were given until Mexico to correct the error without penalty

Didn’t they solve the suspension issue before Sweden? Rallye Magazin news after MC said suspension should be fixed before Sweden and engine before Mexico. I don't remeber anyone reporting otherwise.

http://www.motorsportforums.com/showthread.php?37117-WRC-News-amp-Rumours-(part-V)-2017/page38

[sonnybobiche]

It is not easy to talk about the wing mirror stays when we don’t know the specific tech rules regarding aero (remember form 400/01 WRC), which means the changes could have been provoked by having to comply with some initially grey area in the rules, which was then clarified or they could have come about as a result of evolution in the aero concept of the complete car, i.e. changes to the rear wing might have come as a package deal together with the mirror stays for example.

Yes that form 400/01 is the bane of my existence. Why oh why do they feel the need to be secretive about the damn technical regulations?

For what it's worth I just asked craig scarborough on twitter what he thought of the mirror wings and he said they're probably lousy, very high drag and little downforce. So maybe they got rid of them for that reason.

[mozesii]

Another indication how much of an amateur team they are in their current format.
An upgrade from "village" team.
An amateur team that won a rally before the championship started in Mexico . . . . . .

[N.O.T]

won a rally

you spelled worthless flop of nothingness wrong

[cali]

C'mon this is a tech analysis thread but some of you start to play kindergarten games. Back to topic now, I really do not care to read who spelled wrongly etc.
I would really appreciate if we could return to tech stuff and leave nonsense to Bar talk thread. Thank you!

Sent from my ONEPLUS A3003 using Tapatalk

[pantealex]

Another indication how much of an amateur team they are in their current format.

and Ford´s gearbox thing is indication of Professional Teams way to do things ?

[OldF]

I didn’t find anything in English about the Toyota’s homologation issue in Monte so I did some kind of translations of key issues.


http://yle.fi/urheilu/3-9413001

- Se ensimmäinen asia liittyi auton mittoihin. FIA otti mitat hieman eri paikasta mitan auton pohjalevystä iskunvaimentimen yläpäähän. Siinä taisi olla jokin sentin heitto, ja se johtui lähinnä luokitustodistuksen tulkinnasta.

- The first thing related to the dimensions of the car. The FIA took the dimensions from a little different point from the base plate to the upper end of the shock absorber. There was a difference about one centimetre, and it was mainly due to the interpretation of the homologation form.


- Saimme tähän asiaan muilta tiimeiltä hyväksynnän, voimme osallistua Monte Carlo -ralliin ja korjaamme asiat jo Ruotsin osakilpailuun, Mäkinen täsmentää.

- We got the approval from the other teams for this issue, we can participate in the Monte Carlo - rally and we will fix things by the Swedish rally, Mäkinen explains.


- Toinen juttu oli imuventtiili, jonka alihankkijamme oli vahingossa koonnut neljästä osasta, kun pakoventtiili oli sääntöjen mukaisesti kolmesta osasta. Silläkään asialla ei ole mitään vaikutusta suorituskykyyn, sillä materiaalit olivat aivan sääntöjen mukaisia.

- Another thing was the intake valve which was accidentally assembled of four parts by the subcontractor, when the exhaust valve should consist of three parts according to the regulations. Even that don’t have any effect on performance, because the materials completely comply with the regulations.


Pientä närää aiheutti myös kansainvälisen autoliitto FIA:n halu muuttaa joitakin aerodynamiikkaosiin liittyviä sääntöjä viime hetkessä. lisäkustannuksia tuli usealle tiimille.

A slight resentment was caused by FIA's desire to change some of the regulations of aerodynamics parts at last minute. That caused additional costs for several teams.




http://www.ksml.fi/urheilu/Toyotassa-laittomia-osia-%E2%80%93-kilpailee-Montessa-FIAn-poikkeusluvalla/913752?pwbi=deb2794958af8d2e03fbb2bfb207c983

Tieto Toyotan laittomista osista piti paikkansa, mutta Jari-Matti Latvala ja Juho Hänninen saivat lähtöluvan kauden ensimmäiseen MM-ralliin, koska asia oli etukäteen sovittu Kansainvälisen autoliiton FIA:n kanssa.

The information of Toyota’s illegal parts was true, but Jari-Matti Latvala and Juho Hänninen received permission to start the season in the first World Championship rally, because the matter was agreed in advance with FIA.


M-Sportin tallipäällikkö Malcolm Wilson antoi mielellään hyväksyntänsä Toyotan erityisluvalle.

– Me kaikki teemme virheitä, me mukaan lukien, joten totta kai hyväksyimme Toyotan erivapauden, koska sillä ei ollut vaikutusta auton suorituskykyyn, Wilson korosti.


M-Sport team boss Malcolm Wilson willingly gave his approval for Toyota's special permission.

- We all make mistakes, including us, so of course we adopted Toyota's dispensation, since it had no effect on the car's performance, Wilson stressed.


– Meillä oli eri näkemys mitasta, joka otetaan auton pohjan tasosta iskunvaimentajan yläpäähän. Se ero oli jotain 12 milliä. Toinen asia liittyi imuventtiilin valmistusmenetelmään. Kumpikaan asia ei vaikuta auton suorituskykyyn, Mäkinen vakuutti.

- We had a different view of the dimension, which is measured from car base level to the upper end of shock absorbers. That difference was something like 12 mm. The second case concerned the manufacturing process of the intake valve. Neither of these things do not affect the car's performance, Mäkinen assured.


FIA ja Toyota Gazoo Racing kävivät Yariksen korin luokituksen läpi jouluviikolla.

FIA and Toyota Gazoo Racing made the bodyshell homologation check of the Yaris during the Christmas week.

[J_n_z]

I dont know if it was mentioned before...

C3 has clearly different front suspension setup for gravel and tarmac;
- gravel.. https://pbs.twimg.com/media/C6vbR3DXAAInVgK.jpg
- tarmac (at 0:16) https://www.youtube.com/watch?v=tm0oc1MAk80&feature=youtu.be

[Mirek]

Yes, it was mentioned already in this thread. The tarmac front strut is made in Fabia R5 way while the gravel one is more common type with angled and longer damper.

[AMSS]

Yes, it was mentioned already in this thread. The tarmac front strut is made in Fabia R5 way while the gravel one is more common type with angled and longer damper.

Hyundai R5 also has similar front strut body angle

[Mirek]

Thanks, I have never noticed that. You are right.

http://www.autoklub.pl/news/foto/201609/news20160929_70977h.jpg

[AMSS]

Quit interesting that Hyundai has opted for next to driveshaft mounting on R5 but WRC 17 still has on top of driveshafts mounting (at least based on the pictures I`ve seen)
I think Hyundai now are the only ones with on top mounting of all the WRC manufactorers.

[NickRally]

Image of the Yaris from Rally Mexico reveals (possibly) yet another small Venturi tunnel - the design team appear to have come with a very interesting from aero point of view car.

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[NickRally]

3. Hyundai i20

Finally time for the Hyundai i20 – the car seems very fast and no doubt this is because the complete package is fast rather than one particular thing being exceptionally outstanding. On the floor aero side, it appears less aggressive overall than the Yaris, sitting somewhere between it and the Fiesta, though some features are possibly closer to the Yaris than the Fiesta.

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1293

1294

1295

1296

To be continued in the next post...

[NickRally]

1297

1298

At 1 we can see the diffuser transition point with maybe touch more gentle curvature than the Yaris (could be optical illusion though), which would suggests touch less pressure suction peak, but more forgiving and stable one, though once again this is more applicable to a circuit racer with very low ride height than a rally car. The diffuser appears less steeply inclined (2) than the Yaris, once again suggesting the design team has been after a bit more forgiving downforce, albeit potentially sacrificing some headline numbers. The quantity of strakes (3) is similar to the Fiesta.
An interesting feature of this car’s diffuser is the second curvature region (4) past the mostly planar middle part of the diffuser, which is unique to the i20. In my experience this hasn’t been very effective on a circuit racer, but maybe they tried to regain some of the headline numbers without causing too much peaky-ness. Or the whole diffuser arrangement could be a result of what they can package given road car components in this area (i.e. curved transition from floor, followed by flat-ish region followed by another curved section) in order to have a longer diffuser for the same exit height, see image below:

1299

At 5, as already pointed out on this forum by Ctesibios, is the small but very aggressive Venturi channel ahead of the rear wheels – it is very steeply raked and I wonder if the air stays attached there, though ahead of the wheels, all sorts of amazing things happen. Nevertheless it is smaller than the one on the Yaris and its suction peak will be further rearwards.
The floor of the i20 appears relatively rough (6) to what I am used to, but maybe certain features can be used to benefit the aerodynamics, like the longitudinal railings. Either that, or the design team did not consider these components to be too penalising or of sufficient importance, to change the design direction from the traditional rally floors.
The offset exhaust (7) is embedded in the diffuser, once again feature unique to the i20 with all the other cars opting for central exhaust above the diffuser. I suspect they have done this for packaging, but I could be wrong. Nevertheless, the fact that the exhaust is embedded in the diffuser closer to its transition point from the floor, means its effect might be more powerful. Or, once again, it might just be a packaging exercise.
At 8 is a good view of the complete diffuser and its more square appearance relative to the Yaris with its gradual sides.
9 shows a mismatch between the two suspension guards in their sitting relative to the rest of the floor with the wheels in fool droop, presumably caused by road damage. Or, if the design was too optimistic, it might be that the actual suspension travel have distorted one of them. On another note, I wonder how much the curvature (10) of these guards helps aero downforce creation – I know they are not very rigid, but even so.
11 shows the lack of front Venturi channels, while 12 represents an interesting idea about potential duct, channelling air from underneath the car to the top surface.

[itix]

Very nice read as usual :)

[mozesii]

Educative

[NickRally]

I am sure you have been wondering how long before I use the upside down image of the Yaris from Corsica (Hanninen’s unfortunate off), so here it is with few notes.

http://www.geocities.ws/rallytech/aero/toyota/yaris_aero_10.jpg

http://www.geocities.ws/rallytech/aero/toyota/yaris_aero_11.jpg

[Kris82]

I have a question about center differentials on the new 2017 spec cars. How do they work exactly. The way I understand it the active center differential can be either open or locked and the state is hydraulically controlled with help of electronics. While locked, front and rear axles act as if there was no differential (like in previous models) and when it's open it acts like a front open differential on a regular road car, when one side loses grip then it spins out robbing the torque from other side. The active part lets it go between both states depending on the data from a number of sensors. The power split between the axles is 50/50 on WRC cars as far as I know (correct me if I'm wrong). Now what confuses me are the problems Ogier had faced in Rally Corsica. His hydraulics had failed and he ended up with a rear wheel drive vehicle. Shouldn't he had ended up with an open differential instead, since the hydraulics would be responsible for locking the center differential?

[NickRally]

Hi Kris82, very valid point and one that has puzzled me too. Assuming what was said about ending with rear wheel drive only as a result of the problem is correct (which is by no means certain), then maybe the centre diff on the Fiesta is not of the usual epicyclic gear type with clutch pack to vary the degree of locking, but maybe it uses two clutch packs each controlling the flow of torque to the front and rear axles. This would permit infinite degree of variability in the proportion of torque send to the front and rear axles. I am not sure how reliable such device on a current WRC car will be, but to the best of my knowledge it is used on the current Focus RS to distribute the torque between the two rear wheels in place of the usual epicyclic type rear differential.
I need to watch the footage from the first Sunday stage (only seen the power stage so far) and see if Ogier’s car really behaves like a rear wheel drive one and if the statement to that effect is likely to be correct or just an expression by a frustrated driver (if of course my memory is correct and it came from Ogier).
Regards,
Nick

[Fast Eddie WRC]

Interesting interview with Mads Ostberg including quite a bit about the 2017 car's active centre diff, plus the info from M-Sport not being shared with Mads team...

https://www.podbean.com/media/share/pb-qu8kn-69e93e

[dimviii]

then maybe the centre diff on the Fiesta is not of the usual epicyclic gear type with clutch pack to vary the degree of locking, but maybe it uses two clutch packs each controlling the flow of torque to the front and rear axles. This would permit infinite degree of variability in the proportion of torque send to the front and rear axles. I am not sure how reliable such device on a current WRC car will be, but to the best of my knowledge it is used on the current Focus RS to distribute the torque between the two rear wheels in place of the usual epicyclic type rear differential.
I don't think that is any chance to have just 2 clutch packs and not epicyclic gear type center diff.Imho such application will not be reliable and capable at wrc level,its almost not reliable at street cars(focus rs)

[dimviii]

The way I understand it the active center differential can be either open or locked and the state is hydraulically controlled with help of electronics. ?
no they are not just ''opened'' or ''locked''
they can be opened.locked,and semilocked at countless theoretically positions depenting if you are at a corner,at brakes,if you are with steering at straight or some degres left/right ,the gas pedal position etc.

[SubaruNorway]

Doesn't seem like the Focus RS is a car you would use on an ice track all day, some diff problems in this video from Team O'Neil.
https://www.youtube.com/watch?v=F33BQEXBvok

[Fast Eddie WRC]

Ostberg was saying that although he has previous experience driving active-diff cars, this has not really helped him with the 2017 Fiesta as it a brand new car and there are so many variables to adjust.

He confirmed his car can be 'faster' with the centre diff locked (with better traction), but this also makes the Fiesta more difficult to drive especially setting it up for corners. His team are keeping his car set-up as 'simple' as possible as its impossible to adjust too many settings and know which is actually improving the car's performance.

[itix]

The center differential very likely has a clutch that operates with hydraulic pressure that locks the differential. That means that when there is no hydraulic pressure, the power is sent to where there is the least grip. As the car accelerate, the front lift and the power spins away on the front wheels. That means only the rear wheels have grip which is probably why he had to drive it like a rear wheel drive car.

That's my take on the dynamics anyway.

[Kris82]

no they are not just ''opened'' or ''locked''
they can be opened.locked,and semilocked at countless theoretically positions depending if you are at a corner,at brakes,if you are with steering at straight or some degres left/right ,the gas pedal position etc.

I know there is open and locked and everything in between. I hadn't said it clearly, or you overanalyzed what I had said. :)


The center differential very likely has a clutch that operates with hydraulic pressure that locks the differential. That means that when there is no hydraulic pressure, the power is sent to where there is the least grip. As the car accelerate, the front lift and the power spins away on the front wheels. That means only the rear wheels have grip which is probably why he had to drive it like a rear wheel drive car.

That's my take on the dynamics anyway.

That's what I was leaning towards as well. I was just confused by what Ogier and one of the commentators before him (if I remember correctly) had said during the coverage.

[Mirek]

Ostberg was saying that although he has previous experience driving active-diff cars, this has not really helped him with the 2017 Fiesta as it a brand new car and there are so many variables to adjust.

He confirmed his car can be 'faster' with the centre diff locked (with better traction), but this also makes the Fiesta more difficult to drive especially setting it up for corners. His team are keeping his car set-up as 'simple' as possible as its impossible to adjust too many settings and know which is actually improving the car's performance.

Locked center diff = natural understeering, i.e. slower car everywhere except full acceleration on straight and a car which needs to be driven more sideways to turn.


The center differential very likely has a clutch that operates with hydraulic pressure that locks the differential. That means that when there is no hydraulic pressure, the power is sent to where there is the least grip. As the car accelerate, the front lift and the power spins away on the front wheels. That means only the rear wheels have grip which is probably why he had to drive it like a rear wheel drive car.

That's my take on the dynamics anyway.

No expert here but that makes little sense to me. With opened differential You can't have more torque on one side than on the other. The side with less grip determins the torque going to the other, i.e. the lesser grip on one side the lesser torque the whole system brings but the split ratio is not changed. In extremum when You lift one complete axle it spins but the other stands still as there is no torque on the other side except mechanical friction.

Correct me if I'm wrong.

[Kris82]

You are spot on Mirek. I think that is what itix meant but you described it better. The thing is that in that situation the front would spin out hence making it feel more like a front wheel drive car. I guess in the end the car feel would depend on how the front and rear diffs were set up.

[J_n_z]

I like Focus RS system, because it can do centre and rear diff work only with two clutches (very good price performance solution). But it is actually a FWD car meant to be pushed just here and there for a little while. Still it cant do more than locked diff...

More options has EVO X (if I am not wrong) rear diff, that can accelerete one wheel over the speed of locked diff. But I see no need for such system in a WRC, because it is just a compensation for poor drive skills (it make turn car faster than driver can perform by his own pedal/steering work).

In WRC I think there is no more than a diff with clutch, that can be opened locked or everything in between. It means that it performs at equal for both axles (open) or equal speed (if no gearing is involved) for both axles (locked) or in between.

Regarding Ogires RWD feel... I think it can happen if he had a front diff problem, so that front diff remains open. It means that front axle had just as much torque transfer as the "less grip wheel" allows i.e. less than usual. It means that most of the torque went trough rear wheels.

[NickRally]

You wouldn’t be able to send more torque to the rear wheels (relative to the front) with an open centre diff as explained by Mirek, the only difference opened or locked front diff will make is to provide “the least common denominator” for the whole transmission system, i.e. the path of least resistance or in other words the max torque that can be transmitted through the system.
Looking at it from another angle (which might be what you meant), the combination of open centre diff, open front diff and some state of locking on the rear diff is likely to make the car more stable, i.e. give degree of understeer in general. Whether such comination will make the driver think or feel he has something akin to a rear wheel drive car, don’t really know, might be possible.

[J_n_z]

I will try to explain it again, what I think.

When accelerating from a corner you have: open front diff (defective locking system), locked centre diff (works OK), locked rear diff. (works OK).

In that situation Front and rear axle spin at same speed (locked c. diff) - rear axle works OK, - front inside wheel spins (because it is unweighted) outside rear wheel transfers same amount of torque (open f. diff) as inside one (very little or zero, if wheel is lifted)... effectively you have RWD.

[NickRally]

I see, thanks for clarifying J_n_z – yes, if the problem was on the front diff only, then this will be possible.

[jparker]

Question is, does rally Corsica has so many sharp corners to cause front insight wheel to spin?

[J_n_z]

I think that it can happen in all corners not only in tight ones, it can happen also when cutting corner over grass, or it is half dirty... It also can become difficult to save oversterings.

Definitely WRC car need some locking in f. diff.

[dimviii]

guys you must be a bit confused,front diff at wrc cars have no hydraulics at all.They are plated diffs.
Focus rs 4wd system is a simple and cheap way to have 4wdrive. There is no comparison to active center diff from Mitsubishi evos various editions,which is a proper active diff.

[dimviii]

I will try to explain it again, what I think.

When accelerating from a corner you have: open front diff (defective locking system), locked centre diff (works OK), locked rear diff. (works OK).
.

no its not like that.Accelerating from corners you don't have an opened front diff,neither locked rear diff.

[Ctesibios]

no its not like that.Accelerating from corners you don't have an opened front diff,neither locked rear diff.
The point was IF it was defective, it could act as an open diff. All speculation, as we really don't know at the moment.

[dimviii]

The point was IF it was defective, it could act as an open diff. All speculation, as we really don't know at the moment.

according to Msport they had problems with hydraulics.
Front diff has no hydraylics at all,thats why I said that some are confused.

[Ctesibios]

Anybody know the list of all devices that use hydraulics in the current, 2017, WRC cars?

[NickRally]

according to Msport they had problems with hydraulics.
Front diff has no hydraylics at all,thats why I said that some are confused.

Thanks dimviii, just from curiosity point of view - do we know this for certain (about the mechanical front diff on the current WRC cars) and if yes, one more question – how do we know this :)?