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  1. #421
    Senior Member itix's Avatar
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    Quote Originally Posted by mknight View Post
    Probably a stupid question but doesn't McPherson allow longer max. travel than double wishbone for given size/weight?
    Depends on where you attach the the suspension strut.

    Not necessarily actually. A lot of desert buggys and such have super long travel suspension.


    Edit: or maybe you meant for any given length of the wishbone/control arm. That i can't be sure of, but I'm still not convinced. Theoretically you should be able to manage the same angle of the strut even if you have two suspension arms.
    Last edited by itix; 8th September 2017 at 21:09.

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  3. #422
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    The wishbones on that buggy are half the width of the car. So yes that's what I meant. You can have as much travel, but it will take much more space.
    On McPherson suspension the only thing that will need to be long/extendable is the track control arm no? One "thin" arm that is on the bottom of the car.

  4. #423
    Senior Member itix's Avatar
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    Quote Originally Posted by mknight View Post
    The wishbones on that buggy are half the width of the car. So yes that's what I meant. You can have as much travel, but it will take much more space.
    On McPherson suspension the only thing that will need to be long/extendable is the track control arm no? One "thin" arm that is on the bottom of the car.
    Well unless you design an A-arm with extremely wide cross section at the upper upright link (where the upright or knuckle or hub meets the control arm/A-arm) you can still fit the strut at the same angle. And the attachment point of the strut is lower so for any given space you can attach a longer strut.


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  6. #424
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    Well I know very little about suspension but in a simple hypothetical example:
    - with McPherson you can have the control arm horizontal in the uppermost position and make it half the width of the car. (since it's on the bottom). That gives massive travel (with massive camber change) and there is still a lot of space between the wheels (for engine, cooling etc.)
    - if you want to have as much travel with double wishbone the upper wishbone needs to extend also half the width of the car. Even if the vertical distance between the two wishbones is low it will eat up space between the wheels. (Angling the dampers inwards to give extra space for the upper wishbone also eats space.)

    Or is there something I am missing?

  7. #425
    Senior Member itix's Avatar
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    Quote Originally Posted by mknight View Post
    Well I know very little about suspension but in a simple hypothetical example:
    - with McPherson you can have the control arm horizontal in the uppermost position and make it half the width of the car. (since it's on the bottom). That gives massive travel (with massive camber change) and there is still a lot of space between the wheels (for engine, cooling etc.)
    - if you want to have as much travel with double wishbone the upper wishbone needs to extend also half the width of the car. Even if the vertical distance between the two wishbones is low it will eat up space between the wheels. (Angling the dampers inwards to give extra space for the upper wishbone also eats space.)

    Or is there something I am missing?
    You are absolutely right that they would take more space Since McPherson can be made quite narrow and allow a relatively large engine bay.

    The upper control arm does not actually have to be the same length as the lower one (and isn't really on a lot of applications).

    I imagine the Hoonigan rally cross team are using the fact that the engine is mid mounted to enable them to use the space where the engine would sit on a normal rally car. If you tried to mount this in a regular shock tower without major modifications to the engine bay the control arm would be so short that the camber would change dramatically (unless you pair the lower one to the same length but then you would have massive track width changes and veeeery likely clearance issues, ie like you said... Not as much travel).

    If you want to build a double wishbone rally car with a transverse layout like the modern rally cars, you'd have to make major modifications to the engine bay and shock towers to accommodate an upper control arm long enough.

    Not very practical or desirable I imagine.
    Last edited by itix; 8th September 2017 at 22:15.

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  9. #426
    Armchair General Mirek's Avatar
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    Exactly, You need mid-engine car to have so big suspension travel with double wishbone.

  10. #427
    Senior Member NickRally's Avatar
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    Itix and Mirek - good assessment of the pros and cons of the double wishbone vs Macpherson strut suspensions.
    Given sufficient space and provided it is allowed by the regs (i.e. car does not have to be based on one using Macpherson strut), the double wishbone suspension will offer the most versatility in kinematics parameters coupled with good installation stiffness and offering lower weight relative to other systems for the same installation stiffness.
    Having said that, the Macpherson strut is a very good system and has been successfully used in the past on race/rally cars that have not been constrained to it, with examples from Lancia coming to mind (Beta Montecarlo Turbo front and rear and Stratos rear).

  11. #428
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    Well maybe as somebody who has been working on and modifying suspension on competition vehicles since fall 1973, diassembling and modifying valving internally since winter 1976, and manufacturing suspension since 2003...One serious thing about MacPherson stuff I learned from a Ford engineer in UK whose very first job at Ford when he was first day at Ford was working with Mr Macpherson was this: he said the No1 priority was "acceptable design with eye on production line assembly time.."
    This was early 1950s..He said "It was only much later when we had been rallying the escorts for some time that we saw a second major advantage and that was that we were feeding all the suspension loads into widely different areas of the bodyshell" and that the result being that those areas did not have to be excessively heavy.

    This was of course a much larger issue when there was some connection between a rally car and something made by a car manufacturer---as was the case under Groups 1, 2, 4, A and N...before the "Whirled Rally Car" rules allowed total divorce from reality...

    The fact that all strut designs sees the camber changes drastically and that the tire contact "rolls" all over the place seems to be a shocking side effect and one which is clearly worse as travel goes up......but the obvious increases in speed means if I'm shocked its because its a "theoretical" bad thing but in real life its not nearly as important as the increased travel and the resulting compliance and ability to put power down on acceleration and maintain contact during braking..

    In that respect its just the same advantage/disadvantage calculations we faced on moto-cross bikes 30 years ago when we got the same sort of travel the cars have had in recent length...That acc and braking advantage was more valuable that the loss of precision turning was a disadvantage.
    The modern strut is a pretty amazing design but personally I still have to giggle a bit that it took almost 25 years to get them to the travel we had so long ago.
    John Vanlandingham
    Sleezattle WA, USA
    Vive le Prole-le-ralliat

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  13. #429
    Senior Member NickRally's Avatar
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    All good points Jan.
    On another note, although probably nobody cares, but to correct myself, I mentioned the Beta Montecarlo Turbo as not being constrained to the use of Macpherson strut suspension after making the assumption that the Group 5 cars were pure silhouette racers, but then started having some doubts about that and a quick internet search on the former FIA technical rules ( argent.fia.com/web/fia-public.nsf/whistj?open ) proved that assumptions wrong and revealed that the suspension type of the base car had to be retained. So that leaves the Stratos as the only high level competition car in the more recent history, that comes to my mind at least, that was designed from the ground up with Macpherson strut suspension in mind (using one at the rear).

  14. #430
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    Quote Originally Posted by NickRally View Post
    ..... So that leaves the Stratos as the only high level competition car in the more recent history, that comes to my mind at least, that was designed from the ground up with Macpherson strut suspension in mind (using one at the rear).
    As a formerly active rally driver of a car the highlighted bits mildly put confuse the fuq out of me> .
    I belive that in this sport--and that IS what this forum is all about, the overwhelming majority of high level competition cars in the last 50 years have been strut cars and the number of cars with double a arms exceedingly small....Very short list really of non-strut cars..
    Clearly there is confusion about what you mean by "high level", and also "competition car"..

    My own car was double A arm..and a car with same everything but cylinder bore won a WRC round for decade till the final time in Feb 1976....Opel Ascona B, they did goos as did all the Group b cars except Audi, but that's just a few cars..

    EVERYTHING else has been struts..
    So again, wot da fuq?
    John Vanlandingham
    Sleezattle WA, USA
    Vive le Prole-le-ralliat

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