I need to know what spring rates are recommended for 70 street 30 track.
They have to be linear and for use in coil overs.

 

Why does it have to be linear, doesn't your RS and the GT2 use a progressive spring?

 

I believe the 997 GT2 uses linear front, and progressive rear. Not sure about the 997 GT3, but the 996 GT3 did the the same combo also.

 

Yea good question,KW and Bilstein use linear.

 

Stock systems consist of a SINGLE spring that could be linear or progressive. In the case of the 996 GT3 for example, the front is linear, rear progressive. Progressive meaning of course the spring starts out with one rate and ends up with a second, stiffer, rate. I believe -- not confirmed -- that 997 uses progressive rear spring for all the different versions (Turbo, GT3, etc.).

As far as I know (I am only an amateur whose knowledge comes mostly from wikipedia , anyone please correct me as needed.), most if not all after-market coilovers for the Turbo are stacked springs setup: a linear main spring (a), and a linear second spring (b) called either tender or helper spring, one on top of the other.

A. If the second spring is fully compressed when loaded (with the weight of the car on the coilover), it is called a tender spring and this tender spring does NOT contribute to the overall spring rate. It's there, again AFAIK, to keep the main spring in place during full extension and reduce potential spring noise. The rate of the system equals that of the main spring a. Tender spring rate is very small.

B. If the second spring is not fully compressed when loaded, it is called the helper spring, I think , and the spring rate of the system is b(a/(a+b)) initially, until that second spring becomes fully compressed. Someone checks the math for me. LOL. Once the second spring b becomes fully compressed in a dynamic situation, the system then has spring rate of the main spring, a. You probably could guess already that this system behaves like a progressive single spring system. Helper spring rate is higher than tender's.

I know that Bilstein, KW Variant 3, JRZ, and the Moton all have stacked spring setup. I know that Bilstein system uses a tender spring -- it's fully compressed and does not contribute to the overall rate. I believe (not sure) that none of the after-market coilovers uses progressive spring for either of the 2 stacked springs.