Suspension Sag Calculator
Set race sag & free sag from three measurements — and estimate whether your spring rate is in the right range
This free suspension sag calculator turns three tape-measure readings into race sag and free (static) sag, shows race sag as a percentage of total travel, and helps you estimate whether your spring rate is in the right range for your weight. Built for enduro, motocross, dual-sport and trail riders on KTM, Husqvarna, GasGas, Yamaha, Honda, Beta and Sherco bikes. Works in millimetres or inches.
Measurements
Results
How the three measurements work
L1 — topped out, wheel lifted off the groundL2 — bike on its wheels, no riderL3 — rider seated in full gear, feet upSetup procedure & what the verdicts mean
- L1: Lift the wheel fully off the ground so the suspension tops out. Measure from the axle straight up to a fixed reference (fender bolt or a mark on the slider).
- L2 (static / free sag): Put the bike on its wheels, off the stand, upright. Measure the same two points.
- L3 (race / rider sag): Rider in full gear sits in the normal riding position, feet on the pegs (use a wall or a helper for balance). Bounce and settle the suspension first, then measure again.
- Set race sag with preload until it lands in the target band. More preload means less sag; less preload means more sag.
- Then read free sag to estimate spring rate: too little (or topping out with no rider) points to a spring that is likely too soft; too much points to a spring that is likely too stiff.
Race sag = L1 − L3 · Free sag = L1 − L2 · % = sag ÷ total travel
Guidelines are starting points — always defer to your manufacturer's spec and your own riding preference.
How the suspension sag calculator works
Sag is how far your suspension compresses from fully extended under a given load. This calculator works it out from three measurements taken between the same two points (axle and a fixed reference on the bodywork): L1 with the wheel off the ground and the suspension topped out, L2 with the bike on its wheels but no rider, and L3 with the rider on board in full gear. Race sag (also called rider sag) is L1 − L3. Free sag (also called static sag) is L1 − L2. Enter your numbers and the tool returns both figures, the race-sag percentage of total travel, and whether each one is inside the recommended window for your type of riding.
Race sag vs free sag — what each one tells you
- Race sag (rider sag): How much the bike settles with you on it. It sets ride height and the attitude of the chassis, and you adjust it with spring preload. On many full-size dirt bikes the target is roughly 30–35% of total travel — commonly about 100–105 mm at the rear on a 300 mm-travel bike.
- Free sag (static sag): How much the bike settles under its own weight, with no rider. You do not adjust free sag directly — it falls out of how much preload you needed to set race sag, which makes it one of the best at-home indicators of whether your spring rate is in the right range for your weight.
How to measure sag correctly
- L1 — extended: lift the wheel fully off the ground so the suspension tops out. Measure from the rear axle straight up to a fixed mark on the fender or subframe (for a fork, measure along the slider).
- L2 — static: lower the bike onto its wheels, upright and off the stand, and measure the same two points. Bounce the suspension and let it settle first.
- L3 — race: the rider sits in the normal riding position in full gear, feet on the pegs, balanced against a wall or a helper. Settle the suspension, then measure again.
- Set race sag first by adjusting preload, then read free sag to judge the spring. Measure two or three times and average — a few millimetres of inconsistency is normal.
Recommended sag settings by bike type
Always defer to your manufacturer's manual — these are the typical windows riders actually run. Race sag is shown as a share of total wheel travel; free sag as an absolute figure.
- Off-road / motocross rear: race sag around 100–105 mm on many MX bikes, or roughly 30–35% of rear wheel travel; free sag 30–40 mm.
- Trail / enduro rear: race sag often around 105–115 mm on full-size enduro bikes, or roughly 33–37% if travel is around 300 mm; free sag commonly 30–40 mm. KTM / Husqvarna / GasGas two-strokes are often near 35 mm static and 110 mm rider sag — check the manual for your model and year.
- Street / sport rear: race sag ~25–33%, free sag 20–30 mm.
- Track / race rear: race sag ~25–28% for a sharper, more responsive chassis.
- Front fork: race sag ~28–33% of fork travel, free sag 25–35 mm.
What free sag tells you about spring rate
Once race sag is set with preload, free sag becomes a spring-rate diagnostic. If free sag is too small — or the bike tops out completely with no rider — the spring is probably too soft: you had to wind in a lot of preload to hit race sag, so the bike springs back up too far on its own. If free sag is too large, the spring is probably too stiff: it needed very little preload, so the bike barely settles under its own weight. The right spring lets you hit race sag and land inside the free-sag window at the same time. If you cannot, fit a spring rate matched to your kitted-up weight.
Suspension sag — frequently asked questions
What is race sag (rider sag)?
Race sag is how far the suspension compresses with the rider on board in full gear, measured as L1 (fully extended) minus L3 (rider seated). It sets ride height and chassis balance, and you adjust it with spring preload. Many full-size dirt bikes target roughly 30–35% of total travel — commonly about 100–105 mm at the rear on a 300 mm-travel bike, with full-size enduro bikes often a little more.
What is free sag (static sag) and why does it matter?
Free sag is how far the bike settles under its own weight with no rider — L1 minus L2. You do not set it directly; it results from the preload you used to achieve race sag. That makes it a good at-home indicator of whether your spring rate is in the right range — but treat it as a guide, not a guarantee: stiction, linkage and bearing condition, and measurement consistency all affect the reading, so settle the suspension and average two or three measurements.
How much sag should a dirt bike have?
A typical full-size MX rear shock runs about 100–105 mm of race sag — roughly 30–35% of rear wheel travel — with 30–40 mm of free sag. Full-size enduro bikes often run a little more, around 105–115 mm. Forks run roughly 28–33% of their travel in race sag. Always check your model's manual, as travel and targets vary.
My free sag is too low or too high — what does that mean?
After setting race sag with preload, too little free sag (or the bike topping out with no rider) usually means the spring is too soft — you needed heavy preload to hit race sag. Too much free sag usually means the spring is too stiff — very little preload was needed. In both cases the fix is a spring rate matched to your kitted-up weight, not more preload.
Do I need a rider on the bike to set sag?
Yes for race sag — the rider sits in full gear in the riding position with feet on the pegs while a helper or wall keeps the bike upright. Free sag is measured with no rider. You need both readings plus the fully extended measurement to use the calculator.
How often should I check sag?
Check it whenever you change your gear weight, fit new springs, after a rebuild, or at the start of a season. Springs settle slightly over time and preload collars can creep, so a quick re-measure before a big ride is good practice.