Here it is Tim, the formula for springrates:
Frequency of suspension in cycles per minute(CPM) for racing cars without wings or ground effect is around 100-125. Figures like 160-200CPM are nearer current trends when moving towards the ground effect area.
A formula for McPherson-setup is without suspension leverage, as there is none of it.
CR = ((WF/187,8) x (WF/187,8)) x SW
CR=coil rate; lbs/inch
WF=wheel frequency; CPM
SW=sprung weight; lbs
Its very hard to write a formula like this...hope you get something out of it.
I also found a site that covers the same matter, but much more complicated way:
http://www.theracesite.com/index.cfm...m_article=1233
Justin