Mountain
Bike Spring Rate Calculator V6.0 
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 or millimetres)

Shock Sag: (percentage
of shock stroke) The standard formula uses the Fox Shox
recommended 25% of shock stroke. However, this tends to
calculate too high a spring rate for the majority of riders.
A more appropriate starting point would be 30% to 35%. 
Preload Adjuster: (number
of turns) The standard formula ignores the effect of applying
preload and tends to calculate too high a spring rate. Usually
1.0 is required to lock the spring to the shock body.
Choose a preload value that will allow some plus or minus
adjustment consistent with your required sag level and resubmit.
A zero preload spring rate is found, then preload is applied
to find an alternate spring rate taking into account the
preload spring tension. Calculation is based on a linear
progression. 
EndCoil Effect: (percent)
Closed/Ground compression springs have a typically lower
spring rate in their initial deflection range. The suggested
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
number of turns of the preload adjuster. 









Correction
For Suspension Progression 


The calculator
assumes a linear suspension progression. 
For any deviation
plus or minus <7% use the calculated spring rate. 


Rising Rate
( 7%  15% )  Subtract 50 lbs. 
( may require
more preload )

Extreme Rising
Rate  rare ( 15%  25% )  Subtract 100 lbs. 
( may require
considerably more preload, possibly with a longer stroke
spring )



Falling Rate
( 7%  15% )  Add 50 lbs. 
( may require
less preload )

Extreme Falling
Rate  common ( 15%  25% )  Add 100 lbs. 
( may require
as little preload as possible ) 
( extreme falling
rate suspension bikes should be using an air shock ) 


( 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.



One nameless
publication suggests as much as 50% lighter but you stand
the chance 
of blowing
through your travel when the stable platform compression
filters open up. 


( or simply
ride with the calculated spring rate and let personal preference
decide ) 


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 to avoid coil binding, 
or install a
spring with a longer stroke ( if you can find one that will
fit ). 


Preload does
not change the spring rate. It does change the load capacity,

hence the ability
to vary sag levels with the judicious application of preload.

The calculator
factors in the effect of preload to arrive at an alternate
spring rate. 


Even though
you may be well within the limits for avoiding coil binding,

( as in having
installed a spring with a much longer stroke than the shock
) 
using too much
preload stresses the shock, possibly leading to premature
failure. 




Mountain Bike
Spring Rate Calculator V6.0 

Copyright
(C) 2005 Michael R Young ( mrdy ) 

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. 

http://www.gnu.org/copyleft/gpl.html 


This page
is best viewed in Microsoft Internet Explorer Version 6.0
or higher. 


Roll Your
Own 


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Search for "INITmtbSpringRateCalculatorV5"

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Save again.

voila

your own
calculator 
( if this, or
any alternative method, fails, messageviaemail me to receive
a copy of the original ) 


Anyone wishing
to post this on their own web site is welcome to. 
Simply delete
this "Roll Your Own" portion, specific to this
forum. 
Leave everything
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