MRP
Suspension  Mountain Bike Spring Rate Calculator

Total Riding Weight (pounds):
 The rider's weight with riding gear (average 5lbs
for riding gear weight)

Rear Weight Bias (percent):
 The standard formula is based on a 60:40, Rear to
Front weight distribution
 Add 5% for a heavy rider (+200lbs.)
 Subtract 5% for a light rider (150lbs)
 Add 2% for a recreational or beginner rider (more
rearward bias)
 Subtract 2% for a prolevel or highly experienced
rider (less rearward bias)

Rear
Wheel Travel & Shock Stroke: (inches
or millimeters)

Shock Sag: (percentage of shock stroke)
 The standard for downhill is 30% sag
 The standard for extreme freeriding is 27% sag
 The standard for allmountain riding is 25%

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.










Corrections For Suspension Progression



The
calculator assumes a linear suspension progression.

For
any deviation plus or minus <7% use the calculated spring rate.



Rising Rate
Progressive design, from high motion ratio (+3) to lower ratio (2.4)
> Subtract 50
lbs.

(
may require more preload )

Extreme
Rising Rate
Highly progressive design, from high motion ratio
(+4) to lower ratio (2.4), rare > Subtract 100 lbs.

( may
require considerably more preload, possibly with a longer stroke spring )



Falling
Rate
Digressive design, ends with higher motion than the
start (ex: from 2.4 to 2.8) >
Add 50 lbs.

(
may require less preload )

Highly
digressive design (common with old designs), ends with higher motion than
the start (ex: from 3 to 3.5) >
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
(already factored in formula for MRP Suspension
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 Precautions



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.







