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Steps

Find Your Base PSI: Look for a weight chart on your fork lowers or the manufacturer's website. This gives you a starting air pressure (PSI) based on your riding weight (including gear).
Set Initial Pressure: Attach the shock pump to the air valve (usually on the top left of the fork or shock) and pump to your base PSI. Disconnect the pump.
Reset the O-Ring: Slide the rubber O-ring on the fork stanchion (or rear shock body) all the way down to the seal.
The "Sag" Test: Mount the bike in your riding gear. Lean against a wall or have a friend hold you steady. Stand up in your neutral "attack" position, then sit back down gently. Do not bounce!
Dismount Carefully: Carefully step off the bike without compressing the suspension further.
Measure Sag: Measure the distance the O-ring has shifted from the seal.
- For most trail bikes, you want 25–30% sag.
- Example: If your fork has 100mm of travel, the O-ring should have moved 25–30mm.
Adjust and Repeat:
- If the O-ring moved too far (too much sag), add air.
- If it didn't move far enough (too little sag), release air using the bleed button on the shock pump.
Final Verification: Repeat the test until your sag is spot-on. Write down your final PSI for future reference.

Tips

Always set your suspension while wearing your full riding kit (helmet, shoes, hydration pack). That extra 10–15 lbs makes a big difference!
Sag is a baseline. If you find yourself "bottoming out" (using all the travel) on small bumps, add a bit more air.
Check your pressure every few weeks; air can slowly leak from the chambers just like a tire.