How To Set Your Suspension Sag

When you get your new mountain bike you want it to feel and work its best from the very beginning. Setting up the suspension for your MTB will significantly change how the bike feels, so it’s worth taking the time to get it right. This how-to is specifically for air shocks that use air springs. Coil shocks use metal springs, and sag would be set using replacement coil springs.

You will need a high-pressure shock pump, all your riding gear which includes your pack and any water that you’d normally ride with, and a wall, table or friend to help.

If your fork does not have an O-ring on it, you can use an elastic band or a cable tie, but don't forget to remove it when you're done. Next, if you have compression and rebound settings (or a lockout), turn them all off, or to the open setting. 

You will need to remove the cap that protects the air valve. It is normally on the top or bottom of the left fork leg. Screw the pump onto the valve and start pumping. Don't forget to remove the pump before checking the sag measurement. 

Cycle through your fork's travel by pushing vigorously down on the fork multiple times. This will help to break any stiction in the forks so that when you sit on the bike in the next step, the forks with move smoothly into their sag. 

With both feet on the pedals and hands on the handlebars, get into the position that you would normally ride in. If you're riding challenging terrain where you're often standing up for descents, then get into a standing-up attack position. This will give a more accurate weight distribution on the bike, so get the correct sag setting. 

See where the O-ring is sitting. If it shows more than 25% sag, then add some air into the forks. If it's showing less than 25% then let some air out. Repeat Step 9.

Just like with the forks, some rear shock have a sag indicator on the stanchions (the smooth part that slides in and out) and an O-ring around the stanchion. If your shock does not have sag indicators, then measure the stanchions multiple the length by 0.3 to get the measurement for 30% sag. Rear shocks are usually run at 20-30% sag, with some longer travel bikes running as much as 30-40%, and shorter travel bikes between 15-25%.

You will need to remove the cap that protects the air valve. Screw the pump onto the valve and start pumping. Don't forget to remove the pump before checking the sag measurement. Some manufacturers will have recommended settings for your weight, so start with these. If not, begin by pumping 100 psi into the shock as a starting point. 

Get back on the bike both feet on the pedals and hands on the handlebars. Once again, get into the position that you would normally ride in. If you're riding challenging terrain where you're often standing up for descents, then get into a standing-up attack position. This will give a more accurate weight distribution on the bike, so get the correct sag setting. 

See where the O-ring is sitting. If it shows more than 30% sag, then add some air into the forks. If it's showing less than 30% then let some air out. Repeat Step 17.