The MTB suspension sag calculator checks whether your fork and rear shock are set up correctly for your riding discipline. Sag is the amount of suspension that compresses under your body weight — getting it right unlocks the full performance of your suspension system.
Suspension Sag Settings
Front Fork
Rear Shock
Front Fork Sag
Rear Shock Sag
How to Set Up MTB Suspension Sag
Suspension sag is the most important setup parameter on a mountain bike — more impactful than rebound, compression, or any other adjustment. Getting sag right takes 10 minutes and transforms how your bike handles.
Step 1: Reset Your Suspension
Let the bike hang freely (wheel off ground). Slide the O-ring or zip tie on the fork stanchion or shock shaft all the way down to the seal. For coil springs, mark the shaft with a marker. This establishes your zero position.
Step 2: Measure Static Sag
Wearing your full riding gear, sit on the bike in your normal neutral riding position (not sitting back like climbing). Have a friend hold the bike steady or lean against a wall. Lift yourself carefully straight off the saddle without bouncing the suspension. Measure how far the O-ring moved from the seal — that's your sag measurement in mm.
Step 3: Adjust Air Pressure
Use a dedicated shock pump (not a floor pump). Increase PSI to reduce sag; decrease PSI to increase sag. Add or remove air in 5 PSI increments and re-measure until you hit your target sag for your discipline. Typically, XC riders target 15-20%, trail riders 25-30%, and enduro/DH riders 30-35% sag.
Step 4: Tune Rebound
After setting sag, adjust rebound so the suspension rebounds at the right speed. Too fast (low rebound damping): the bike bucks you off on repeated hits. Too slow (high rebound damping): the suspension packs down and becomes harsh. A good starting point is the manufacturer's recommended clicks from full closed.
FAQ
Is this MTB suspension sag calculator free?
Yes, completely free with no account required. Check your sag percentage and compare to recommended ranges instantly.
What is suspension sag and why does it matter?
Sag is how much your suspension compresses under your riding weight. The correct sag keeps the suspension in its most sensitive part of the travel, allowing it to extend over bumps (small hits) and compress into the bumps (large hits). Too little sag means the bike rides harsh; too much and you bottom out frequently.
How do I measure suspension sag?
Put an O-ring or zip tie on your fork stanchion or shock shaft. Stand over the bike with full gear in your normal riding position. Step off carefully without bouncing. Measure the distance the O-ring moved from full extension — that's your sag. Measure at least twice and average.
What is the target sag percentage for trail riding?
Trail riding typically targets 25-30% sag on both fork and rear shock. At 160mm fork travel, that's 40-48mm of sag. This keeps the suspension mid-stroke where sensitivity and travel are best balanced for mixed terrain.
My fork and shock sag are different — is that okay?
Some difference is normal because fork and shock geometry distribute weight differently. Within 5% of each other is generally fine. If they're very different, check if air pressure in one needs adjustment, or if your bike's weight distribution is unusual (heavy bags, very forward or rearward riding position).
How does air pressure relate to sag?
Increase air pressure to reduce sag (firmer). Decrease air pressure to increase sag (softer). Add air in 5 PSI increments, re-measure, and repeat until you hit your target. Temperature affects air pressure, so check sag after warming up the suspension on the trail.