Help with spring rate

[InnAir]

Can someone tell me how to figure the spring rate of a torsion bar? For example, if I have a 4130 bar 29" long, 1" in diameter, with a 5" lever on one end, what will the spring rate be. I just dont want the answer, but the forumla.
Thanks.

 

[israelkk]

K=(G*J)/L

Where J=(Pi*D^4)/32

G - Torsional Nodulus
J - Polar Inertla os the bar section
D - Bar Diameter
L - Bar length
K - Spring constant