Springs that have length greater than four times the spring diameter will have a natural tendency to bow when loaded. If any friction is produced because of spring bowing the rate of the spring is increased. Generally the more a spring is compressed, the more it will tend to bow. Tips to minimize bowing:
Coil bind occurs in a spring whenever one active coil contacts another active coil. The rate of the spring increases whenever its coils bind since the bound coils are no longer active. Handling is affected by coil bind. If the spring is compressed to solid height during suspension movement, the suspension will cease to work. Check for evidence of coil bind by examining the finish between the active coils. If any coil have bound, the finish between them will show contact marks that appear as though they were drawn with a lead pencil. Springs that are binding should be replaced with either a taller spring, or a spring of the same height that has more stroke available. The potential for coil bind is increased whenever short springs are used. Always us the right spring height.
When a spring takes a set it will normally stabilize at its new height. The rate effectively remains the same since no appreciable changes have been made to any of the three factors that determine the spring's rate. Other than creating a need to readjust the chassis to restore setup and ride height, the spring should provide satisfactory performance. However, in cases where a spring is extremely over stressed, the spring height may not stabilize. The spring may continue to change height (both shortening and lengthening) as the spring is worked. As a result, the setup changes every time the spring height changes. This can cause major chassis tuning headaches!
We recommend that you mark each of your springs and monitor the height of each on a regular basis. Be sure to always measure height at the same point on the end coils. You should suspect that a spring is setting whenever wheel weights continually change. There is more of a chance for a spring to change its height than its rate. A spring should not be used if it has changed more than 2% in height and does not stabilize in height. You should spend your time monitoring spring height and not worry as much about the rate change.
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