How do you determine what the optimal spring rate for your car is? Is there some sort of formula taking into account ride height, suspension travel, vehicle corner weights, etc to determine the "perfect" spring rates for the car? And how would linear vs progressive springs affect this decision?

I'm considering a full on coilover race suspension setup for one of my cars (a 2nd gen MR2), with seperately adjustable compression and rebound dampers(cuz I like to fine tune the handling ), and I need to know what sort of spring rates to choose to make the car handle as good as possible, while not completely destroying ride quality. This will be a street/track day car.

For the purposes of this question I will give an approximate estimate of what I believe the corner weights of the car will be:

LF:~550lbs RF:~470lbs
LR:~690lbs RR:~610lbs

The car should have about 1 1/2" of suspension travel at each corner before the tire contacts the fender.

 

Unfortunately, "optimal" is different for different tracks in different conditions, and is influenced by sway bars. That's why race teams spend so much time testing and trying different setups. Data acquisition has helped shorten the learning curve a lot, but there's still a lot of trial and error.

As far as short cuts and compromises, if you can find someone racing a car very similar to yours that is doing well, and can get them to share their spring and sway bar rates with you, that's a decent place to start.

Otherwise, some of the race shops that set up cars like yours can be of some help. For example, if you call Ground Control and tell them what you're doing with the car, what shocks and springs, etc. that you want to use, they usually have someone knowledgable that can help you out.

For some theoretical background on suspension set-up, Fred Puhn's book "How to make your car handle" is getting old, but it's still a goodie.