How To Set Sag On A Dirt Bike
7 min read · Updated 29 August 2026
Sag is the amount the suspension compresses under weight. Get it wrong and nothing else you adjust will work: the bike will either headshake on the straights or refuse to hold a line in a corner.
You need a tape measure, a spanner or punch for the shock preload collar, and one other person. Ten minutes, and the bike will feel like a different machine.
Target numbers
Race sag is what you set. Static sag is what you then measure to check the spring rate is correct for your weight.
| Measurement | Motocross | Enduro / trail |
|---|---|---|
| Race sag (rider aboard, full kit) | 100–105 mm | 105–110 mm |
| Static sag (bike only) | 25–40 mm | 30–45 mm |
Step by step
- Put the bike on a stand with the rear wheel fully off the ground. Measure from the rear axle centre vertically to a fixed reference point on the rear fender or subframe. Write it down — this is your unloaded measurement.
- Take the bike off the stand. Sit on it in full riding kit, feet on the pegs, in your normal riding position, with a helper holding the bars.
- Bounce the rear a couple of times and settle. Have the helper measure between the same two points. Unloaded minus this figure is your race sag.
- Adjust the shock preload collar: tighten to reduce sag, loosen to increase it. As a rough guide one full turn changes sag by around 1.5–3 mm, depending on the shock thread pitch and linkage ratio — so always re-measure rather than counting turns.
- Repeat until race sag is in range, then tighten the lock collar properly.
- Now measure static sag: bike off the stand, nobody on it, same two points. Unloaded minus that figure is static sag.
What static sag tells you
- Race sag correct and static sag under 25 mm: your rear spring is too soft — it is being over-preloaded to hit the number.
- Race sag correct and static sag over 45 mm: your rear spring is too stiff, with almost no preload dialled in.
- Race sag correct and static sag between 25 and 40 mm (most riders aim for 30–35 mm): the spring rate matches your weight. Move on to clickers and fork height.
Common mistakes
- Measuring in shorts. Kit, boots and body armour add several kilos and change the number.
- Sitting further forward than you actually ride, which flatters the reading.
- Using different reference points between measurements — mark them with tape.
- Forgetting the front. Once rear sag is set, check fork height in the clamps before touching any clickers.
- Chasing sag on a shock that is overdue a service — worn oil and a tired seal head will never give a consistent reading.
After sag, in order
Set sag, then fork height, then compression damping, then rebound. Change one adjuster at a time in two-click steps and ride the same section of track between changes. Anything else is guesswork.
Common questions
What should race sag be on a dirt bike?
100–105 mm for motocross with the rider in full kit, and 105–110 mm for enduro or trail riding where more comfort and traction is wanted.
Can I set sag on my own?
It is far more accurate with a helper. Alone, you can get close using a zip-tie on the shock shaft or a sag scale tool, but the seated riding position is hard to hold steady while measuring.
How much does one turn of preload change sag?
Somewhere around 1.5–3 mm per full turn of the preload collar, depending on the shock and linkage ratio. There is no universal figure, so adjust, re-measure and repeat.
Should I set sag before or after changing springs?
Set sag first with the springs on the bike. Static sag then tells you whether the spring rate is right; if it is out of range, fit correct springs and set sag again.
More guides
Dirt Bike Maintenance Schedule
Every job on a dirt bike, mapped to the engine hour it is due at — in one table you can actually work from.
Dirt Bike Suspension Setup Guide
Set sag correctly, then change one clicker at a time — with a symptom-to-fix table for harsh forks, headshake and a bike that kicks.