Health & Fitness
Bike Suspension Sag Calculator
Updated Aug 27, 2026 Reviewed Aug 27, 2026
Calculate fork or rear-shock target sag, compare measured displacement and estimate one cautious air-pressure or coil-rate adjustment.
Measure, adjust once, measure again
Set suspension sag from the O-ring
Result
Calculation summary
Enter values to see the result
Your result, breakdown, assumptions, and warnings will appear here.
Live suspension preview
Target travel before damping
Target sag
30 mm
Measured sag
22%
Next setting check
94 psi
The O-ring displacement is compared with a target percentage, then one spring-setting iteration is shown.
How to use this calculator
- 1Enter manufacturer travel or shock stroke and target sag.
- 2Measure O-ring displacement in full riding equipment.
- 3Enter the current spring setting, make one controlled change and remeasure.
Formula
sag % = displacement ÷ travel × 100
Next setting is a proportional iteration from the current measured setup.
Calculation steps
- Calculate target millimetres.
- Compare measured sag.
- Scale one air-pressure or coil-rate iteration.
Worked example
A 150 mm fork at 20% targets 30 mm; 33 mm at 85 psi suggests checking near 94 psi next.
Assumptions
- Sag follows the maker's procedure.
- Rider wears normal gear.
- Spring response is approximately proportional for one iteration.
- All manufacturer limits take priority.
Sources
Frequently asked questions
Is this a model-specific pressure chart?
No. Begin with the exact manufacturer chart and refine using measured sag.
When should I tune rebound?
After spring support and sag are established.
Can it choose a coil spring?
It only scales a known current rate; confirm every hardware and preload requirement.
Why remeasure?
Friction, air chambers, leverage and rider position make proportional estimates imperfect.
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