Spring Rates for a Mutant 7 Clone

[hoss4659]

Building a light weight street rod/auto cross car. Basic chassis/design of a 7. Widened, stretched to accommodate a trans-axle, IFS, IRS. Trying for a curb weight of under 1300#, distribution close to 50/50. Need advice on:

1) How to find target spring rates for the front and rear.

2) What resistance (lbs./inch) to use for stabilizer bars, front and rear.

 

A search of the archives was productive except that all the responses failed to note the inclination angle of the coil-overs. The suggestion of using between 0.5 to 1.0 X the corner's sprung weight could be useful. Chapman's comment that the prime mission of the suspension system is to keep the tire patch in contact with the road surface and that (before aerodynamic aids) this is best done with a compliant (as opposed to stiff) suspension, has always made a lot sense to me.

 

Advice, opinions, suggestions as well as references to online calculators

are all welcome.

[JohnK]

One pretty fundamental measure is wheel frequency, which gives you a sportyness figure - 120 cycles per second is reasonable for a seven. This is figured for each corner by dividing the coil rate by the square of the suspension leverage, dividing that value by the sprung weight, taking the sq root of that value and multiplying it by 187.8.

 

After that, things become complicated. An anti-roll bar is a tuning device which is dependent on suspension geometry and weight. Linkages determine what each component does at each instant as the car is under way. Wm.C. Mitchell makes an affordable product called WinGeo3 and a companion product by Rowley will allow you to see the effect (understeer or not) of different roll bars. Overall, there is not "an answer" or a good starting set of specs, and ANY solution involves a lot of compromises bundled into a guess... but its also a lot of fun, esp when things turn out well.

Edited November 13, 2011 by JohnK

[JohnK]

Oops - thats cycles per MINUTE.