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Author Topic:   Spring Rate
Dirt Roller

Total posts: 18
posted April 07, 2005 05:36 AM  
What is the formula for calculating the spring rate at the wheel.( for the rear tires)I looked in the tool box and all thats there is for a swing arm calculation.Thanks in Advance.

Dirt Forum Champ
Total posts: 505
posted April 07, 2005 07:58 AM  
You need to calculate the motion ratio to find the wheel rate.

The front is pretty simple
k=spring rate
a=length of lower a-arm
b=length to spring mounting point

Spring rate at ball joint=k(b/a)^2

Due to the live axle in the rear, calculating the rear motion ratio is a little more complex.

a=length of svsa
b=distance from ic to spring mounting point
sw=distance between rear springs
tw=track width

Wheel rate=k((b/a)^2(sw/tw)^2)

That gives you the wheel rate in roll, to calculate the wheel rate in bump you remove the (sw/tw)^2 part of the equation.

Now if you springs are mounted to birdcages the equations get even more complicated and almost easier to caclulate by physical measurements as opposed pure mathematics.

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