Differences between Automotive Engineering and Motorsports Engineering

[petany]

I still cannot figure it out.
Take Roll Center Movement for example, the theories obviously are almost the same, however, according to the references I've read, it seems people don't care too much about it when designing an automobile, whether it's Kinematic R.C. or Force-Based R.C., while it plays an important role when it comes to a race-car.
I don't know if this conclusion is true cause I cannot find answers anywhere in any books.
Could anyone please tell me what're the differeces in design process between automotives and race-cars(especially on the considerations of suspension and steering)?

 

[BrianPetersen]

Priorities.

Main consideration for a street driven car is stability under almost all foreseeable circumstances. If a street driven car goes backwards into the ditch, lawyers will have a feeding frenzy. Street driven cars understeer ... period.

Next after that are comfort, ride quality, NVH (noise vibration harshness), load carrying capability, and only then some degree of cornering capability. Those might be in slightly different order depending on the type of car, but cornering prowess is not at the top ... stability is. Otherwise ... you'll be hearing from the lawyers.

Obviously, on a race car, it's pretty much the other way around, and many of the characteristics that are vital qualities in a street car are of no consideration whatsoever in a race car.

 

[GregLocock]

" according to the references I've read, it seems people don't care too much about it when designing an automobile, whether it's Kinematic R.C. or Force-Based R.C"

Sorry that says more about the books you've read than what people like me do.

Saab used to have a theory about moving the roll centre around.

I read a fairly thorough (proprietary) investigation of 'roll centres' a few years back, the upshot of which was that in cornering it is very hard to define what you mean by roll centre, and that FBRC and GRC move in different ways during a cornering event. I tend to look at the change in forces at each balljoint during the cornering event rather than worrying too much about constructing some notional centre to react the contact patch forces through.

We do use GRC in particular as part of the steering budget, early in a program, and changes of the order of 10mm are taken seriously. Later on in the program we measure FBRC, and there changes of the order of 10mm are of the same order as the statistical measuring errors of the rig. At that point the cars are tuned by the drivers, not by worrying about RCs as such.






Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[JohnLear]

Priorities that may affect handling etc might have nothing to do with the suspension per se.

These days nearly all sedans seem to feature fold down rear seat backs that expose a large aperture between the cabin and boot (trunk) cavities, to allow long cargo to be carried. In the old days this area was usually 'triangulated' with a stressed skin.

Deleting this panel might make the marketing people happy (improving the cargo carrying versatility, which certainly looks like a good idea...), but it also (appears to) significantly reduce torsional chassis stiffness (and hatches seem even worse in this respect than sedans, with even less rear stiffness).

My subjective experience has been that bracing this particular aperture tends to significantly improve handling responsiveness, with some noticable lessening of understeer. It may be that this reduction in responsiveness / increase in understeer might be seen as 'desireable' by the company lawyers...?

 

[MacGyverS2000]

Street driven cars understeer ... period.

Tell that to my S2000... she'll handle a lot better than most street cars, but when she decides to go beyond the edge, she tucks her nose in first. Oversteer was by design on this car.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[MintJulep]

Saab used to have a theory about moving the roll centre around.

My early Saab 900 was the nastiest tempered car I ever had. No tolerance at all for mistakes when driven near the limits on loose surfaces, snow or ice. Let the back end slide just a millimeter too far and whop! The ass snapped around.

It's the only car I've ever driven that I had unintentionally spin on me.

Marvelous car for chewing up distance on the highway though.

 

[patprimmer]

Mint

Have yo ever driven an old swing axle VW Beetle.

I did a lot of my early driving in one. It certainly taught me how to cope with the switch from uncertain under steer to sudden and extreme over steer. The oversteer characteristic i still a feature I enjoy.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[Rob45]

Ah, Pat!
If you liked swing-axle VWs, you'd have loved my old Spitfire:
THERE was a car with "trailing-throttle oversteer," as it used to be called; I learned that no matter how badly you'd misunderestimated a turn, you dare not lift off the gas! I have a picture somewhere of that car in a slalom event with both rear tires off the ground in a turn.

I did have a chance to meet Don Gates once upon a time, after he'd left GM and opened I think it was Antares Engineering; in the course of a long rambling quasi-interview, he taught me how to fix the Spit's handling by removing roll resistance from the rear suspension and adding it back to the front.

But to get back to the original topic: the fundamental difference between racecars and production automobiles is you have to be able to build and sell the latter at a profit; this requirement drives quite a number of decisions.