8.4 suspension

Rear Shock Air Pressure & Sag

Rear Shock Air Pressure & Sag. Step-by-step procedure for bike maintenance — tools, time, and what to watch out for.

Difficulty ★☆☆ easy
Time ~10 min
Applies to Full-suspension bikes (most MTB, some E-bike)

Tools

  • Standard workshop tools

Procedure

  1. Locate the air valve

    on the shock — usually on the air can.

  2. Note current pressure

    with the shock pump.

  3. Slide the rubber O-ring

    down against the air can seal.

  4. Set up the bike on level ground.

  5. Get on the bike in normal riding gear and posture.

  6. Bounce gently to settle, then hold static.

  7. Dismount carefully.

  8. Measure the O-ring position

    from the seal to determine sag.

  9. Sag percentage

    = (O-ring travel) / (total shock stroke) × 100. Stroke is often printed on the shock — e.g., "210x55" means 55 mm stroke.

  10. Adjust pressure

    to dial in sag to your target (usually 25–30% for trail/enduro, 20–25% for XC). ---

Procedure #

  1. Locate the air valve on the shock — usually on the air can.
  2. Note current pressure with the shock pump.
  3. Slide the rubber O-ring down against the air can seal.
  4. Set up the bike on level ground.
  5. Get on the bike in normal riding gear and posture.
  6. Bounce gently to settle, then hold static.
  7. Dismount carefully.
  8. Measure the O-ring position from the seal to determine sag.
  9. Sag percentage = (O-ring travel) / (total shock stroke) × 100. Stroke is often printed on the shock — e.g., “210x55” means 55 mm stroke.
  10. Adjust pressure to dial in sag to your target (usually 25–30% for trail/enduro, 20–25% for XC).