Kirk,

Neither Tune or Engineer to Win give a formula...perhaps Prepare (which I don't have)

For a solid bar:

Rate (Pi * G * D^4)/(16 * B^2 * L)

Where G= Modulus of elasticity of material

D= Diameter of Bar

B= Length of lever arm (measured 90 degrees to length of bar---not along the lever arm) Adjacent not Hypotenuse

L= Length of bar

4130 C34-C38 has a G of 1.2 x 10^7

I obtained this formula from a suspension engineering class I took years ago--pre FSAE type programs.

You will be guessing on the modulus of elasticity, so perhaps this will get you close enough to at least get the right OD bar...you can then tune with the lever arm. Geometry of the links and mounting bushings will also effect things, but at least it will be a good starting point.

Perhaps ADDCO has a site with a formula or a sprint car website/chat forum might be of some help.

on edit--for a hollow bar my notes say to substitute (O.D.^4 - I.D. ^4) for the "D^4" in the solid bar formula.

Using a 1" solid bar vs 1" hollow w/.125" wall gives a change of about 40%

Happy engineering!

Daryl DeArman


[This message has been edited by Quickshoe (edited May 18, 2004).]