What is sag?
Sag is how far your suspension compresses when you're just sitting on the bike in your normal riding position. It keeps the wheels on the ground over dips and bumps. Too little makes the ride harsh, and too much can make you bottom out on big hits.
How to measure sag
- Gear up. Wear your helmet, shoes, and a full hydration pack, the same way you ride.
- Open the suspension. Set any lockout or compression lever to open.
- Start near the right pressure. Use the setup chart from your fork or shock maker if you have one.
- Set the o-ring. Push the rubber ring down against the seal. No o-ring? A loose zip tie works.
- Get on carefully. Lean against a wall or have a friend hold the bike, and settle into your riding position without bouncing. The suspension compresses and moves the ring.
- Step off gently. Try not to compress the suspension any further on the way off.
- Measure. Measure from the seal to the o-ring in millimeters, then enter it above.
How to adjust it
- Too much sag: add air. Too little sag: let some air out.
- Change it in small steps. Fox suggests about 5 PSI at a time, then measure again.
- Coil spring? You can't add air. Small changes come from the preload adjuster, and bigger ones need a different spring.
- Set sag first. Do it before you change any rebound or compression settings.
Where these numbers come from
Fox suggests starting at 25%, going a few points lower for XC and a few points higher for downhill. Bike and fork makers vary from there: rear shocks are often set around 25% to 35%, and forks often run less sag than the rear. Our ranges are a middle ground across those guides, so if your bike's manual gives a number, use that one.