Originally Posted by italyix
Although the above calculates a rear spring at a little over 400lb, it is actually around 500lb (600*0.83 = 498lb)
This would complement the front 500lb nicely.
Sway bars then can provide more "spring" when you need it (cornering that is)
If you list numbers then perhaps you should do the math correctly:
Wheel rate = spring rate * motion ratio^2 so for your example...
600*0.83^2 = 413 lbf/in
Good luck finding any reputable shop/vendor that builds/races e9x M3s that would recommend running F/R 500/1200 lbf/in spring rates with the rear spring in the stock location