Mountain Bike Spring Rate Calculator

Total Riding Weight: ( pounds ) includes the rider and anything else added to the bike: lock, water bottles, etc.

Rear Weight Bias: ( percent ) The standard formula is based on a 60:40, Rear to Front weight distribution. A more accurate way would be to use a bathroom scale under the rear wheel and a 2x4 under the front wheel to determine the true sprung weight at the rear wheel. Position your body according to your riding style. Enter this value for total weight and 100 for Rear Weight Bias. Alternatively use 55=XC, 65=FR, 70=DH, all others use the standard 60.

Rear Wheel Travel / Shock Stroke: ( inches )

Shock Sag: ( percentage of shock stroke ) The standard formula uses the Fox Shox recommended 25 of shock stroke. A zero-preload spring rate is determined, then preload is applied to calculate the corresponding sag. Choose a sag appropriate to your riding style. If you are an extreme rider ( jumps, drops, big hits, etc ) you should run less sag and a correspondingly higher spring rate.

Preload Adjuster: ( number of turns ) A minimum of 1.0 is required.

End-Coil Effect: ( percent ) Closed/Ground compression springs have a typically lower spring rate in their initial deflection range. The canned value is a best guess of the effect ECE will have on preload adjustment. It is a percentage of the overall spring rate used in calculating the spring tension for the specified turns of preload.

Input Parameters
Total Riding Weight ( lbs )
Rear Weight Bias ( % )
Rear Wheel Travel ( in )
Shock Stroke ( in )
Shock Sag ( % )
Preload Adjuster ( n.n )
End Coil Effect ( % )
Output Parameters
Leverage Ratio ( Travel / Stroke )
Calculated Spring Rate (lbs/in)
Suggested Spring Rate (lbs/in)
Suggested Spring Rate Preloaded Sag ( % )

Optional Spring Rates
Spring Rate ( lbs ) Shock Sag ( % ) Shock Sag ( in )
*** *** *** *** *** ***

Preload Precautionary
Preload adjusters apply about 1mm or .039" per turn.
If the spring is not marked as to its real stroke never use more
than 2.0 turns on the preload adjuster too avoid coil binding.
If the spring is marked as in 600# x 1.63" or 600# x 41mm
calculate the available preload by spring stroke minus shock stroke.
Be Careful
Even though you may be well within the limits for avoiding coil binding,
using a lot of preload stresses the shock leading to premature failure.

Correction For Suspension Progression
Anything plus or minus <7% can be ignored.
Rising Rate ( 7% - 15% ) - Subtract 50 lbs.
Extreme Rising Rate - rare ( 15% - 25% ) - Subtract 100 lbs.
Falling Rate ( 7% - 15% ) - Add 50 lbs.
Extreme Falling Rate - common ( 15% - 25% ) - Add 100 lbs.
( or simply ride with the calculated spring rate and let personal preference decide )

Correction For Stable Platform Shocks
If you have already corrected for suspension progression try a
50 pound lighter spring, otherwise try a 100 pound lighter spring.
Some suggest as much as 40% lighter but you stand the chance of blowing
through your travel when the stable platform compression filter opens up.
( or simply ride with the calculated spring rate and let personal preference decide )

Reference Links

Mountain Bike Spring Rate Calculator V4.0

Copyright (C) 2004 Michael R Young

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

To receive a copy of the GNU General Public License write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.