You need to start out with what you shock / spring combo is and figure out the rest from there. Take me for example. When I had stock worn out springs with airbags in the rear I was able to pull 1.6 60's with DR's on a 12 second car. Now that I have stiffened the chassis, put on SPC springs, and Bilstien HD's, my rear end lifts up when I hit the gas and the tires let loose. This is because my instant center is now 2 feet in front of the car thanks to the lower center of gravity and change in suspension geometry. The stiff springs / shocks only hurt that more. The only thing I can do to fix it now is adjust the rear control arms to get that instant center moved back. I will be buying the UCA kit from Baseline Suspensions to do this.