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killroy · 07-28-04, 03:14 PM

[ QUOTE ]
Torsional rigidity (TR) is not correctly expressed as a function of the weight of the car.

[/ QUOTE ]

I have to disagree a bit. The relation ship between chassis loads and vehicle weight is pretty straight forward. The heavier the car, the higher the load on the chassis. So one chassis will behave similarly to another with half the stiffness in a car that weighs half as much.

Of course the ratio of sprung to unsprung mass will change things a bit, wheel base and track are certainly factors, but in general it's pretty close to a linear relationship.

My point is that no one needs a 25,000 ft lb per degree chassis, 2,000 ft lbs per degree would work (drivable), and if you have more than 5,000 ft lb per degree, you won't gain very much by stiffening it further.

American road cars in the 60's had around 2-3,000 ft lbs per degree. The average car was a little bit stiffer in the 80's. Computers and crash test standards made big improvements in the 90's, now all of the manufacturers know how to make a unit body chassis with very high stiffness and crash safety.

Mure stiffness is always better, but just because a new Audi has a huge number does not mean that you car won't handle if it has less.

07-28-04, 03:14 PM	#13 (permalink)
killroy A Tenth Join Date: Jul 2004 GT40: Silicon Valley Posts: 121 Rep Power: 6	Re: Deflection Figures for a GT40 Chassis [ QUOTE ] Torsional rigidity (TR) is not correctly expressed as a function of the weight of the car. [/ QUOTE ] I have to disagree a bit. The relation ship between chassis loads and vehicle weight is pretty straight forward. The heavier the car, the higher the load on the chassis. So one chassis will behave similarly to another with half the stiffness in a car that weighs half as much. Of course the ratio of sprung to unsprung mass will change things a bit, wheel base and track are certainly factors, but in general it's pretty close to a linear relationship. My point is that no one needs a 25,000 ft lb per degree chassis, 2,000 ft lbs per degree would work (drivable), and if you have more than 5,000 ft lb per degree, you won't gain very much by stiffening it further. American road cars in the 60's had around 2-3,000 ft lbs per degree. The average car was a little bit stiffer in the 80's. Computers and crash test standards made big improvements in the 90's, now all of the manufacturers know how to make a unit body chassis with very high stiffness and crash safety. Mure stiffness is always better, but just because a new Audi has a huge number does not mean that you car won't handle if it has less.