Motorcycle Suspension Sag Calculator
Calculate motorcycle front fork and rear shock sag in mm from three points.
Returns spring preload adjustment and target sag for sport, touring, and off-road.
Suspension Sag Analysis
Suspension sag is how much the bike compresses under its own weight (free sag) and under the rider’s weight (race sag / rider sag). Proper sag ensures the suspension works in its optimal range — not too stiff, not too soft.
Two measurements:
- Free sag (static sag): Bike on stand with no rider. Measures spring preload.
- Race sag (rider sag): Rider aboard in riding position. This is the key setup number.
Target race sag values:
- Sport/superbike: 25–30 mm rear, 30–35 mm front
- Naked / roadster: 30–35 mm rear, 35–40 mm front
- Adventure / dual-sport: 85–100 mm rear (longer travel)
- Cruiser: 30–40 mm rear
How to measure:
- Measure full extension (bike on paddock stand, wheel hanging free) = L1
- Measure under rider weight = L2
- Race sag = L1 − L2
Interpreting results:
- Race sag too HIGH (>target): Add preload (compress spring more)
- Race sag too LOW (<target): Reduce preload
- Free sag should be 5–10 mm (rear). If free sag is 0 with correct race sag, the spring rate is too stiff for rider weight.
Spring rate guide: A rough starting point is 1 N/mm of spring rate per 10 kg of total weight (rider + gear + luggage).