Garage tool
Sag calculator
Three measurements, five minutes, and the single biggest improvement most bikes can get for free.
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Measure from the rear axle centre to a fixed mark on the fender, and use the same mark all three times. Have someone hold the bike upright for L3 while you sit in your normal riding position.
The tool shows your readings and your manual’s figures only. It does not judge your spring: take these numbers, and your bike’s stock spring rate, to a suspension shop.
How to measure
L1 — get the rear wheel off the ground so the suspension is fully extended. Measure from the centre of the rear axle to a mark on the rear fender directly above it. Use the same mark for all three measurements.
L2 — bike on the ground, no rider. Push down on the seat and let it settle, then lift and let it settle, and take the middle of the two readings.
L3 — sit on the bike in full riding gear, feet on the pegs, in your normal riding position, with someone steadying the bike. Settle it the same way, then measure.
What the numbers mean
Race sag is how far the bike settles with you on it. It is set with preload, and it is the first thing to get right.
Free sag (the manuals call it static sag) is how far it settles under its own weight. Where your manual prints both figures, the tool lines your readings up with them.
The tool does not judge your spring. Which spring to fit depends on your bike’s stock rate, your weight in gear and how you ride: take these readings to a suspension shop before buying.