You're browser has JavaScript disabled. You will not be able to use the calculator. The basic formula used for calcualting the spring rate is:

Rate = (wireDiameter^4 * 1470000) / (coilDiameter^3 * numberCoils)

This is valid for all steel springs. Not valid of other types.

Shock / Fork Spring Rate Calculator

If you have ever wanted to be able to determine what strength springs are on your bike you can use this information to help you figure it out. You'll need to be able to measure the spring by itself. That means it has to be removed from the shock or forks. The three measurements you need from your spring are:

Wire diameter - the diameter of the wire used to make the spring.

Coil diameter - the outer diameter of the coil.

Number of coils - the number of free coils. It can be a fractional amount.

All dimensions in decimal inches. The default values are a 89 yz250 front fork

Wire Diameter:

 in

Spring Outer Diameter:

 in

Number of Free Coils:

Kg/mm




Related Spring Tips and Notes

"To count free coils this is what I do. Do not count the coil at each end that is flatened and really used for seating. starting where the spring "takes off" from the base coil, I count full coils from this point on, and then do my best guess as to fraction of coil before returning to the base coil at the other end. Basicly once the free coils touch the base coil, the spring is done. The base coil can't provide any springing, and thus isn't free." mtiberio


Formula:
((diameter of the wire)^4) * 1470000
---------------------------------------------------- = answer(lb/in) / 56 = spring rate kg/mm
((diameter of the spring - diameter of wire)^3) * (number of coils)

^4 means to the 4th power
^3 means to the 3rd power
The diameter of the spring or coil is measured from the OD of the coil and subtract the wire diameter. All dimensions in inches, returns rate in kg per mm. This formula works because all of the various spring steels used in suspension springs have the same nominal bulk modulus. This will not work for hi-tech titanium springs. you'll notice that with the number of coils in the denominator, this implies that two springs identical except for number of coils, the one with the most coils is softer.

"Why doesn't the number of coils per inch come into play? If you have ever looked at a progressive spring, you'll find that one end has the coils closer together than the other. The rate is constant across the spring reguardless of the coil spacing. What happens is once you begin to use the spring, the coils that are close together finally touch (coil bind) reducing the number of free coils, (making the denomenator smaller in the equation) and increasing the spring rate for the remaining unbound coils." mtiberio