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Jeff: Thanks for the spreadsheet calcs! Yes that helps. The masses I listed are the sprung not unsprung. The unsprung for the front is 108 lbs and the rear is 107 lbs. Interesting! GM made three different sets of springs for the Kappa platform (SKY/SOLSTICE). Model codes: FE2 - front 128...

I think its all relative. My car presently has spring rates of 211 lb/in in the front and 285 lb/in in the rear. This equates to ride frequencies of 1.12 and 1.34 Hz. The car is RWD, has understeer, but does a reasonable good job of getting around the autocross course. I've ridden in my...

I may do this next year, but for now I'm modifying my coilovers so I can easily change the springs. Part of this process is selecting a starting spring rate. I'm steering towards stiff springs to start with due to the natural of autocross courses. Autocross courses are short, in the half mile...

Thanks Greg. If I set the front ride frequency at ~3 Hz should the rear be ~10% less? My design goal is for improved autocross track performance. The speeds on course are less the 60 MPH and the surface is generally pretty flat with the minor disturbances you find in parking lots. The...

cibachrome: Thanks for your reply. Sorry, I messed that up. I meant the sprung mass. From what I've gathered it's good practice to set the rear 10% faster than the front. The idea is to keep the upsets in phase with the front. I believe this is for a better ride. That being said my object...

Is the correct? Below is the calculation I used to determine my spring rates for auto cross racing. My target natural frequency is 2.2 in the front and 2.5 in the rear. The calculation is three steps, finding the wheel rate, find the wheel rate in series with the spring rate of the tire and...

Cool! :) Thanks Brain. So if I use a 10 inch free spring lehgth instead of the 12 inch keeping the same rate of 225 lbf/inch than the compressed spring length will be 6 inches, (free length 10 inches) - (897/225 inch). The ride height will change by [stock compressed spring length ((15 inch) -...

Thanks for the replay Greg. Your are correct about the motion Ratio. I'm only considering the shock and spring travel. The MR is .73 for the front end and the coilover is mounted at a 60 degree angle from the horiaontal plane. I thought that the spring only carries the unsprung weight? You...

Are these assumptions correct? I want to change the springs on my 2008 Saturn Sky to increase the natural frequency (NF) and lower the center of gravity (CoG). The stock front spring has a spring rate of 128 lbf/in, a free length of 15 inches and a compressed length of 10 inches. The spring...