Chassis Stiffness

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Chassis Stiffness

Postby 1stMiata123 » Sat Oct 16, 2010 12:18 am

I have looked through miata.net and there is a thread going about stiffness of the miata and its benefits. I have found a couple great articles on specific products, and F1 car articles explaining how is works. What I am trying to find is the answer to OP original question, and now the answer to my own. Will chassis stiffness make a faster car? There seems to be a lot of guess' in the m.net thread. I am not looking for the science of it anymore, but does anyone have any data. Before and after. Track times, anything on paper? I find it hard to believe its a "wash" as some people have put it. I know the added weight slows the car, but there has to be good reason to the products being developed and people paying so much money for them. Any other articles, or explanations would be great as well, just so I can learn more. Thank you in advance.
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Re: Chassis Stiffness

Postby KAP » Mon Nov 01, 2010 11:01 am

1stMiata123,

I'm not a big race driver, just an average everyday Miata driver who like to push his car a bit and do the occasional road rally. I will admit, quietly, to being a licensed Professional Engineer... So I do feel that I can offer some textbook answers to your questions...

You asked "Will chassis stiffness make a faster car? "... The correct response is... yup, you guessed it, both No and Yes... First off, It will not make the car any faster in a straight line. That's a simple war between the power you plant to the ground vs all the associated drags and frictions trying to turn all your fuel into heat one way or another... Second, if you're are talking about cornering.. well then the answer may be yes... Body flex and suspension movement all take energy. The source of the energy is predominantly from your powerplant, ie your engine. Short of going downhill on Lombard St in SF, your energy source is your engine. The less energy lost in flexing body and suspension the more you have to plant in those rear wheels.. The big caveat?? the theory is all based on smooth level surfaces... Something that is really rare on a road course. If the course is rough, then the flex may actually help you by keeping your tires in better contact with the road. Wheels up in the air don't seem to help accelerate or brake a car too well...

Of Course, even on a smooth course, there are limits. If you exceed the coefficient of friction between your tire and the pavement you will slide or spin a tire and all the saved energy will end up converting rubber compounds to smoke..

So why do so many folks sell chassis stiffeners, Frog bars, X bracing, Tower Strut Bracing? It has to do with knowing where your flex is occuring and being able to control or adjust it to suit the road surface. If you start with a stiff chassis, you can dial in your flex via your choice of suspension, sway bar and tire pressures... Chassis flex is rarely consistant from side to side or front to back. Who wants a car that corners radically different when turning right or left and accelerating or decellerating? With a stiff chassis and adjustable suspension, you can have handling consistancy that may help you learn to be a better driver. It helped me... If you need crisp cornering on a smooth track, dial the stiffness up, if you need compliance to keep the wheels on the ground, dial it down. Both can lead to faster track times.. That's why the hardcore racing folks put so much time into reading the tracks and tuning the cars to the track..

Not a simple answer, I know, but I hope it helps....

KAP
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Re: Chassis Stiffness

Postby slartibartfast » Mon Nov 01, 2010 8:22 pm

There are a lot car mods based upon theoretical improvements. I consider chassis stiffening on a street car to be in that category. Luckily, there is little downside to added stiffeners. At worse they add a few pounds and lighten your wallet. At best they improve the feel of your chassis and allow your to drive closer to the suspension limits with confidence.
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