Mountain Bike Coil Spring Rate Calculator
Rear-shock static force estimate
Find a coil spring starting rate
Result
Calculation summary
Enter values to see the result
Live spring preview
Load, leverage and sag set the baseline
Rounded rate
525 lb/in
Average leverage
2.73
Target shock sag
15.4 mm
The model compares the rounded rate with adjacent available springs so the trade-off stays visible.
How to use this calculator
- 1Enter total ready-to-ride system weight and measured rear load share.
- 2Enter rear-wheel travel, shock stroke, target sag and actual preload geometry.
- 3Compare the rounded starting rate with adjacent available springs and remeasure sag on the bicycle.
Formula
spring rate ≈ rear wheel load × average leverage ratio ÷ (shock sag + preload)
The model uses average leverage and static force balance to create a starting point.
Calculation steps
- Convert total weight to rear-wheel static load.
- Calculate average wheel-to-shock leverage ratio and target shock displacement.
- Resolve ideal rate, round to available increments and predict sag for nearby rates.
Worked example
A 95 kg ready-to-ride system with 60% rear load, 150 mm wheel travel and a 55 mm shock targeting 28% sag produces a starting point near 525 lb/in with 1 mm preload.
Assumptions
- System weight includes rider, equipment and bicycle.
- Rear weight bias is measured or selected by the user.
- Average leverage ratio approximates a linkage that may be progressive or regressive.
- Shock and spring fit must be checked against the exact manufacturer model.
Sources
Frequently asked questions
Why is this only a starting rate?
Real linkage leverage changes through travel, and rider position, damping, friction and riding style alter the measured result.
Does preload make a spring stiffer?
No. Preload changes initial force and sag, but the spring rate itself remains unchanged.
Can I use rider weight only?
Use ready-to-ride system weight when possible because bicycle and carried equipment also contribute to static wheel load.
Does a matching rate guarantee the spring fits?
No. Free length, inner diameter, stroke capacity and shock-specific limits must be checked separately.