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Originally Posted by Bramick
General basic question. How to assess suspension stiffness. Someone made a commitment about how my car has very little lean. How stiff is too stiff. Other then track times what else could I do to dial. Apologies for the general question. I'm not sure where to start to learn more.
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If you want to start dialing in your suspension, I'd start looking at tire temperatures and pressures first. At the end of your session, stop as soon as you can (in pit lane, if allowed) and record tire pressures while they're still hot.
As a general rule of thumb, though, you want the suspension to be as soft as you can get away with. On the Viper project where we redesigned the suspension from scratch, increasing compliance (of the suspension as a whole, not like bushing stiffness) was a major goal of ours. The car previously had 1200lb/in springs in the rear with a low motion ratio (0.6) and now it's down to 800 lb/in at 0.8 MR. That's a HUGE difference in allowable deflection over on-track disturbances, and we can already tell a big difference in performance. The car just ignores bumps and dips that used to be super disturbing.
For an 86, we're still figuring out the "magic" spring rates for a track setup. We're running the Tarmac 2 shocks and springs for now. We're planning to soften up the rear spring rates, since we weren't happy with the ride frequency split and Myles (at RCE) suggested a softer rate.
Low body roll is generally a good thing since it speeds up weight transfer, but if it comes from stiff springs that put too much of the burden on the tires, it'll adversely affect how the car drives over bumps and imperfections. How does the car feel over bumps on the track? Like, here at Cresson, there are two big bumps on track we look at for examples of high shock speeds. One's at the exit of Big Bend, and the other's at the entry to Buzzard Neck. Do you get loose over those?