Motocross Rider Sag Calculator
Calculate static sag, rider sag and rider-sag percentage from your measurements.
Sag measurements describe how far the rear suspension settles from topped-out length. This tool performs the arithmetic; it does not prescribe the correct sag for every motorcycle because targets depend on chassis, suspension design and setup.
Use the same two measuring points every time. Measure with the bike unloaded/topped out, then bike-only, then rider in normal riding position with gear. Repeat measurements until they are consistent.
How to use this tool
Measure between the same fixed points with the rear suspension fully extended, then with the bike supporting its own weight, then with the geared rider in normal riding position. Consistency of the measuring points matters more than convenience.
The tool subtracts bike-only and rider-loaded measurements from topped-out length. If wheel travel is entered, it also shows rider sag as a percentage of that travel. Repeat the physical measurements before adjusting preload.
Worked example
With 600 mm topped out, 565 mm bike-only and 495 mm with the rider, static sag is 35 mm and rider sag is 105 mm. Those are calculated values—not a statement that 105 mm is correct for every bike.
Using it at the track
Sag is most useful as part of a repeatable setup routine. Record the motorcycle, spring/preload configuration, rider gear, measurement points and track conditions so a later value has context. A change in sag after several ride days can also be a prompt to inspect preload, linkage or suspension condition rather than simply turning the adjuster back to an old number.
Have a helper take the measurements so the rider can stay centered in normal riding position. Bounce the suspension lightly and let it settle before reading. If repeated measurements vary several millimeters, solve the measurement inconsistency before chasing setup changes.
Before using the result
- Use your motorcycle or suspension provider’s target range.
- A sag number cannot diagnose incorrect spring rate by itself.
- Recheck sag after spring/preload changes and after suspension service.
Limit: Correct targets vary by motorcycle, suspension setup and use. Use the service manual or suspension provider for acceptable ranges and spring/preload limits.