Motorcycle Sag Calculator (Rider Sag & Static Sag)
Work out motorcycle suspension sag from three measurements — fully extended, bike only and with the rider on — and see rider sag as a share of travel, the target range for street, track or off-road and which way to adjust preload.
How it works
rider sag = L1 − L3 · static (free) sag = L1 − L2 · sag % = sag ÷ total travel × 100 · target rider sag ≈ 25–33% of travel for street, 25–30% track, 30–35% off-road, 28–33% loaded adventure · measure L between a fixed point on the chassis and the axle
Sag is how much the suspension compresses under the weight of the bike and rider. Setting it with spring preload puts the suspension in the right part of its travel, so it can extend into dips as well as compress over bumps, and it sets the bike's ride height and steering geometry. Measure each end three times — fully extended, on its own weight and with you aboard — ideally with a helper and bouncing the bike to cancel friction. If the preload needed to reach the target leaves static sag far too small or too large, the spring rate is wrong for your weight.
Worked example
A rear shock with 130 mm of travel measures 600 mm fully extended (L1), 585 mm on its own weight (L2) and 565 mm with the rider aboard (L3). Rider sag = 600 − 565 = 35.0 mm, or 26.9% of travel — within the 32.5–42.9 mm street target. Static sag is 15.0 mm.
Sources: Race Tech — How to measure sag · Penske Racing Shocks — Setting motorcycle front suspension sag
Frequently asked questions
How much sag should a motorcycle have?
A common rule is about a third of travel or a little less: 25–33% for street bikes, 25–30% for track, 30–35% (around 100 mm on a 300 mm shock) for motocross and enduro. Check your manufacturer's or suspension tuner's figures for your bike.
What is the difference between rider sag and static sag?
Static (free) sag is how far the bike settles under its own weight; rider (race) sag is how far it settles with you on board. Rider sag is set with preload; static sag tells you whether the spring rate suits your weight.
Should I add or remove preload?
Too much sag means the spring is too soft for the load — add preload. Too little sag means too much preload — back it off. If you cannot reach the target within the adjuster's range, change the spring.
Do I set front and rear sag separately?
Yes. Measure and adjust each end with its own travel. Changing rear sag also changes the bike's attitude and steering, so check the front again afterwards.
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This calculator is for educational purposes. Double-check important results before acting on them.