CalculatorsRear Shock Spring Rate Calculator

Rear Shock Spring Rate Calculator

A coil has one rate. This estimates the lb/in that sags the requested percent of stroke with about 70% of rider weight on the rear wheel.

Inputs

Rider weight (lb)Leverage ratioShock stroke (in)Target sag (%)

Results

Spring rate: 475 lb/in
Spring rate: 83 N/mm

How the number is made

Rate (lb/in) = (rider lb × 0.70 × leverage) ÷ (stroke in inches × sag fraction). N/mm = lb/in × 0.175. Leverage is the average ratio from the frame’s kinematics, not the yoke length.

Progressive linkages sag differently from a constant-leverage bike. Confirm on the shock with a riding-kit sag check.

Related calculators

Fork Sag and PSI Calculator
Set the front before you judge the rear spring on one ride.
Flip-Chip Geometry Calculator
A flip chip can change leverage and bottom-bracket height together.

Questions

Where do I find leverage?

The frame maker publishes a leverage curve. Use the average, or the value at sag if they print one.

Why both lb/in and N/mm?

US springs are sold in lb/in. European springs are often N/mm. Same part, two labels.

Does the spring rate include the bike weight?

The spring uses about 70 percent of rider weight as the rear share, times leverage, over the sag portion of the stroke. Bike weight is not added on top.

Related gear

Coil spring
Buy the rate you calculated and one step either side if the shop will swap them.
$30–$80

Disclaimer — no professional advice, no liability

These calculators are simplified estimates for education. They are not a bike fit, a structural inspection, or a torque specification that overrides the number printed on a part. Confirm chain length, spoke length, tire fit and bolt torque on the bicycle before you ride.

These calculators, pages and any related content are provided “as is” and “as available”, solely for general educational and informational purposes. They are simplified mathematical estimates, not a professional bike fit, a structural inspection, a manufacturer torque specification or a training, nutrition or medical plan.

Results can be wrong, incomplete or inapplicable to your frame, wheels, tires, drivetrain or suspension. You must independently verify every figure, assume all risk, and confirm chain length before you cut, spoke length before you lace, tire and rim compatibility before you inflate, and the torque printed on the part before you tighten it.

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