I don't know how to calculate spring rates. I'm planning on getting gc coilovers, supposedly you can get them with different rates, I don't know what to get. I want it to ride firm, but I don't want to be knocked out of the seat with every contour of the road. My shock valving is 375/120 front and 300/100 rear. I don't know what those numbers mean, but they're what the guy at bilstein decided on when I talked to him. The car probably weighs about 2600-2700 lbs.
Thanks for any help..