CJSUSPENSION SETUP TOOL

Coil Spring Rate Calculator

Calculate a coil spring starting point using rider load, rear-wheel travel, shock stroke, target sag and the best leverage information available for your frame.

Frame database Sag-point leverage Full curve support Matched spring links

Bike and frame

Select a verified frame entry or enter the dimensions manually.

Frame Manual setup Rear-wheel travel

Shock stroke

Average leverage ratio 2.46 : 1 Rear-wheel travel ÷ shock stroke

Leverage information

Rider and load

Use riding weight with helmet, shoes, pack, water and normal equipment.

Rider weight with gear

Bike weight

Extra cargo

Only enter weight not already included above.

Rear-wheel load method Estimate from weight bias Fastest method. A measured wheel load is more accurate. Measured rear-wheel load Use scales under both wheels at equal height, in your normal riding stance.

Rear weight bias

65% is a useful gravity-bike starting estimate. Measuring the rear-wheel load is preferred.

Advanced load correction

Rear unsprung mass correction

A wheel scale includes rear wheel and other unsprung mass that is not carried through the spring. Leave at zero unless you have a defensible measurement or estimate.

Sag and spring setup

The target sag controls the calculated static spring requirement.

Target rear-wheel sag

48.0 mm rear-wheel sag Spring-rate increment Recommendation preference This selects between practical rounded rates. It does not secretly alter the physics calculation.

Advanced preload and spring travel

Minimum installed preload

Maximum preferred preload

Preload collar movement per turn

Confirm the actual value for the shock. This only converts preload millimetres into estimated turns. Spring marked travel, optional

Used for a basic coil-bind travel check. Enter 0 if unknown.

Recommended spring 450 lb/in

78.8 N/mm

Theoretical zero-preload rate 450 lb/in

Practical exact rate 425 lb/in

Required preload 1.5 mm About 1.5 turns

Expected sag 30.0% With the calculated preload

Calculation breakdown

Rear sprung load used: 62.4 kg
Average leverage ratio: 2.46 : 1
Leverage ratio at sag: 2.46 : 1
Rear-wheel sag: 48.0 mm
Calculated shock compression: 19.5 mm
Frame progression: Not supplied
Data confidence: Average-ratio estimate

MATCHED TO YOUR RESULT

Shop the correct spring rate and stroke

Product links update automatically from the calculated spring rate and entered shock stroke.

Confirm shock fitment and spring internal diameter before ordering. Super Alloy Racing springs may require the correct POM spacers for your shock brand.

This is a setup starting point, not a guarantee of compatibility or final ride preference. Confirm shock fitment, spring internal diameter, spring travel and permitted preload with the shock and frame manufacturers.

HOW IT WORKS

A transparent calculation, not a hidden lookup

Rear load

The calculator estimates or uses a measured static load carried by the rear suspension.

Leverage at sag

A sag-point ratio or integrated leverage curve is used when available. Average leverage is the fallback.

Spring force

Required shock force is divided by spring compression at the selected sag to calculate the spring rate.

Practical spring

The exact result is converted to an available rate and checked against the requested preload range.

How to Choose the Correct MTB Coil Spring Rate

Use the CJSuspension coil spring rate calculator to find a practical starting spring rate for your mountain bike rear shock. The calculation considers your riding weight, bike weight, rear-wheel travel, shock stroke, target sag and the best available leverage-ratio information for your frame.

For the most accurate result, select your bike from the frame database or enter its leverage ratio at sag. When detailed frame data is unavailable, the calculator uses the average leverage ratio calculated from rear-wheel travel and shock stroke.

Your result includes a recommended spring rate, softer and firmer alternatives, required preload and expected sag. It also matches your setup to the correct Super Alloy Racing and Sprindex spring-rate range and shock-stroke length.

The result should be treated as a setup starting point. Frame kinematics, rider position, riding style, suspension design and personal preference can affect the final spring choice. Always confirm spring fitment, available travel, preload limits and measured sag after installation.

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Copyright and permitted use

© 2026 CJSuspension Limited. This calculator and its original code, content, interface and database are protected intellectual property. Copying, scraping, adapting or using it to create a competing tool is prohibited without written permission.