MotoTunerBlog · 21 Aug 2026 · 8 min
How to measure motorcycle sag
Sag is how far the motorcycle sits in the suspension stroke. It is the first chassis number that matters on a track day. Clickers will not save a bike that is sitting at the wrong ride height.
Static sag is the bike alone on the ground. Rider sag (race sag) is the same measurement with the rider in full kit, both feet on the pegs. Too little sag and the bike sits high: harsh, won’t use the tire, steers heavy. Too much sag and it wallows, uses up travel, and can tuck or squat.
What you need
- A zip-tie or a sag tool on the fork stanchion and the shock shaft
- A helper to hold the bike upright
- The same boots and leather you will race in
- A note on the setup sheet — do not “remember” the number
The method
- Fit the zip-tie. Zero on a stand — wheels hanging, ties pushed down to the seal.
- Static: bike only, on the ground, no rider. Measure the drop from the zero mark.
- Rider / race sag: full kit, both feet on the pegs. Helper holds it upright. Bounce once, settle, measure.
- Repeat front and rear. Same helper, same stance, same boots.
- Set preload. Ride. Do not chase clickers until sag is honest.
Sportbike rider-sag windows
Starting windows in the Öhlins / Race Tech style — percent of travel, then millimeters on a 120 mm fork:
| End | % of travel | On 120 mm |
|---|---|---|
| Front rider sag | 23–28% | 27.6–33.6 mm |
| Rear rider sag | 25–30% | 30.0–36.0 mm |
| Front static | — | 5–10 mm |
| Rear static | — | 5–15 mm |
Dirt, adventure, and supermoto use the same formulas with different percents. MotoTuner grades the window from the bike’s class and travel, not a poster on the wall.
Preload turns — and when the spring is wrong
Preload moves you in the stroke. It is not a substitute for spring rate.
Worked example from the handbook: 80 kg rider + 8 kg gear, 120 mm fork, 38 mm measured front rider sag. Sport front window is 27.6–33.6 mm (mid 30.6). 38 mm is too soft.
Error = 38 − 30.6 = 7.4 mm. Fork collar pitch is about 1.0 mm per turn → about 8 turns of preload. On a shock at 1.5 mm/turn that same error is about 5 turns.
If the error is more than 15 mm, the spring rate is wrong for rider + gear. The collar will run out. Change the spring. MotoTuner flags that so you stop adding preload to a hole clickers cannot fill.
Why this is the first pit-board number
Most “the bike won’t turn” stories start here. A square front tire and a 2 psi miss are next. Damping is third. If you skip sag, every clicker change is a story about a bike that was never in the window.
MotoTuner is a pit-board app, not a race engineer. Calculators are handbook rules of thumb. You own how the motorcycle is set.