Technical Analysis: WRC Cars 2017

[janvanvurpa]

In the past a centre diff with asymmetric torque split was in use. The example is from “few” years back in the 1986 Portugal rally which had both tarmac and gravel stages.
The Lancias had a front/rear torque split 25/75 on gravel and 30/70 on tarmac.
The torque split for the Audis was 40/60 all the time.
Malcom Wilson had with the MG Metro a torque split of 35/65 on tarmac and 45/55 on gravel. The other Metro drivers had 25/75 on tarmac and 35/65 on gravel.
The Fords had a torque of split 37/63 all the time.

The active front and rear diffs was banned from the beginning of 2006. If I recall correctly there was also talk about banning the active central diff but at least the drivers wanted to preserve it because it enabled the use of the handbrake. https://en.wikipedia.org/wiki/World_Rally_Car

The rule changes from season to season can be followed on http://juwra.com/seasons.html
The ban of the front and rear diffs is not on Juwra’s 2006 rule changes http://juwra.com/rules_2006.html
Jonkka must have missed it for some reason.

All the manufacturers attending the 1995 wrc season had an active centre diff by the end of the year.

Even looking at the era I like the best, the Group A days between say 88 to 94 its seems that everybody just made all the diff stiffer than hell..Front , center, rear, crazy stiff.. Now add wide tires and tight narrow tarmac roads and you have a car horrible to try and do tight corners...

There there was toque split on those cars...who know but I DO know that many in the Sierra/Sapphire/Escort Cossies did go to 50/50 and to quote one multiple BTRDA Gold Star winner, Pete Doughty, "It handled like a pig, like the old Quattros but 50/50 was the fastest so that is what you run"

[dimviii]

Jerónimo Aliaga‏*@jerowrc
Diferencias aerodinamicas ente @TOYOTA_GR y @HMSGOfficial en la previa del #WRC #RallyArgentina2017

[mknight]

Well I can see the Toyota "pods" are wider at the bottom, but can't see any change to Hyundai at first sight.

[NickRally]

Watching the redbull.tv rally Argentina day 1 recap where, as usual, they start by talking about the previous rally, Corsica in this case, and at 3:23-3:33min from the start of the program Ogier talks about his problems, though I don't know what day of the rally that applies for (I am yet to watch the wrc+ daily highlights from Corsica) - anyway, when talking about his problems he says "diff was locked" and "no hand brake". The significance of this is that if the issue was lost hydraulic pressure, then it means the diff is normally locked when no hydraulic pressure is applied to it. This is possible though I haven't got experience with such arrangement. I am more familiar with the usual normally non-locked diffs that need hydraulic pressure to lock them.
In my view though, it is more likely that they use the normally unlocked diff and the problem would have been in the control electronics, that must have necessitated to manually force the system into a locked state or the control mechanism reverts by default to locked diff state when issues are encountered. The locked diff would then of course explain the lack of hand brake.
The issue above would be the exact opposite of having rear wheel drive only car, but there might have been different problems each day, though the handling of the car from the first Sunday stage on TV appeared to match a car with locked centre diff and no hand brake (overshooting hairpins).

[NickRally]

And now Ostberg - no centre diff and no hand brake

[Mrpengski]

Hey NickRally, I enjoy reading your analysis on aero, it's always good to hear an outside opinion Keep it coming!

I think every team did well to hide the extra girth required for the new side impact regulation. Only when you see one from this angle that you realise they are basically pushed out to the regulation width at the waist.
side.jpg

[fecksfx]

Very interesting to read through and try to follow.
Watching the WRC show with a couple of rear diffusers being lost in water splashes, the footage showed it as a significant loss of rear traction with spins in tight corners. Is the down force at slower speeds really likely to be that affected or is that just the footage that was available?

Sorry for the poor grammar, hopefully it makes sense.

[NickRally]

Thanks Mrpengski, I absolutely love the appearance of these new cars.

Hi fecksfx – I doubt the contribution of the rear diffuser to rear/overall grip at low speeds is significant enough to be the cause of the spins you mention. Let’s make an estimate (probably way too optimistic) for the total downforce in gravel trim as 200kg at 150kph and let’s say the contribution of the diffuser to this number is 30 percent (again probably way too optimistic considering the gravel trim ride heights) - this would represent 60kg at 150kph. Now if we reduce the speed down to say 50kph, then the contribution of the rear diffuser will be [(50/150)^2]*60 which is 6.67kg – figure low enough to be lost in the overall noise of the “experiment”. If you add to this that the cars will be very much sideways in such corners (i.e. significant yaw angle), then the contribution of all aero devices will drop even further, though some teams appear to have paid more attention to downforce creation in yaw than other teams. And to add even further point here, the Fiesta diffuser appears to be the most benign of the lot, which means if lost will have less of an effect on downforce. All three other teams have more aggressive diffusers and I suspect they will feel it a bit more if they lose it, but again not at these low speeds. Nevertheless the Fiesta diffuser attachments appear to be a bit fragile with all these instances of broken ones – I am sure the M-Sport guys will be discussing how to improve the attachments in their faults meetings.
I suspect the most significant part that a missing diffuser plays, is in the head of the driver, which in itself is of course a problem.

[Lundefaret]

Hey NickRally, I enjoy reading your analysis on aero, it's always good to hear an outside opinion Keep it coming!

I think every team did well to hide the extra girth required for the new side impact regulation. Only when you see one from this angle that you realise they are basically pushed out to the regulation width at the waist.
side.jpg

This is actually the most important change of the 17 rally cars, and also the most road car relevant. It should actually be used in road cars as soon as possible, because as it is for a rally car, side impact is the weakest link also for road cars.

[Mirek]

I don't think that such large safety side zones are realistically possible for road cars. It would add a lot of cost and reduce practical use (or internal space). For example imagine that You add 100 mm on door thickness. Now You park at a mall. Your car is wider, i.e. You have less space around and moreover You need to open the door 100 mm more to be able to get outside. My car is not that big (Octavia III) but very often I can barely get out of it when parking in the city. Another problematic thing is that especially for women the wider and heavier door would be likely difficult to manipulate (especially when You don't park on a leveled ground but on the slope), maybe they would require electric motors, i.e. more cost and more potential issues after crashes.