Originally Posted by tampamax
Why would you put 700lbs springs in the rear and 600lbs springs up front? Aren't you trying to control the wieght on braking and conering as much as possible? If so then should the heavier springs be supporting the heaviest part of the car?
While I can't comment on automobile physics, I can tell you that it's common practice on E36 and E46 M3s to place heavier springs in the rear. For example, the spring rates from the factory are 160ish front and 460ish rear.
Of course, the biggest factor at play is what the driver wants. I've tried three spring rate combinations on this car: 550f/500r, 700f/800r, and currently 600f/700r. I like the latest combination best because it works really well with the car's alignment specs (Front: 3.5 camber, 1/16 toe out, maxed caster; Rear: 2.3 camber, 1/16 toe in) and yields a car which is easy to drive, neutral when pushed, and comfortable on the street.
The really amazing thing about this car in particular is that it's comfortable and quiet (no creaking, squeaking, groaning, etc) on the street, and yet a weapon on the track - zero slop. I attribute that to the suspension (TCKline and I specced out this kit totally custom) and the wide wheels and tires.