F650 Spring Rate Calculator FAQ
compiled and edited by Brad #1002
much of the content was provided by cugino pegaso
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before attempting any work in this FAQ.
For FAQs related to forks, shocks, maintenance and aftermarket
Spring Rate Calculator
If you have ever wanted to be able to determine what strength spring
is on you rear shock or in the front forks you can use this information to
help you figure it out. You'll need to be able to measure the spring.
That means it is best if it can be removed from the motorcycle. If you
don't want to remove the spring you at least need to be able to reach it
to measure it. Of course, the springs in the front forks can't be
measured without being removed. See
Forks Maintenance FAQ for more on
how to remove the fork springs.
The three measurements you need from your spring are:
- Wire diameter - the diameter of the wire used to make the spring.
Typically about .5 inches.
- Coil diameter - the diameter from center to center of the coil.
It can be calculated if you know the outside diameter of the coil and
wire diameter (O.D. - Wire Dia.)
- Number of coils - the number of free coils. It is often a
fractional amount like 4.2.
The formula used to do these calculations is provided in case you are
away from your computer and just want to use a calculator. The '^'
notation indicates 'to the power of'. This formula applies to steel
rate = ( wireDia^4 * 1470000 ) / ( coilDia^3 * numCoils )
Related Spring Tips and Notes
- Given that we have linkage rear suspensions (1 rear wheel
movement translates into less than 1 of shock movement). An increase of
100#s/ at the spring, is less at the wheel. cugino pegaso
- To count free coils this is what I do. Do not count the coil at
each end that is flattened 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. Basically 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. cugino pegaso
- 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 regardless 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 denominator smaller
in the equation) and increasing the spring rate for the remaining unbound
coils. cugino pegaso
- Other sites to visit with suspension information are;