Welcome to our Ask a Mechanic column where our expert mechanic Daniel Slusser answers your bike maintenance questions. If you have a question for Daniel, please post it on our Facebook Wall or e-mail Daniel directly at firstname.lastname@example.org. Today’s column will review how to adjust a trail bike suspension fork.
I just got a new Fox Float 32 RL 140 and wanted to see if you had any tips on how to set it up for a 185 lb. rider. The fork is mounted to a Giant Trance if that helps. From: Nate
There is no reason to fork over your sanity getting your suspension adjusted. Tuning a fork like the Fox 32 Float RL is relatively easy because there are only two variables to adjust, these are: air pressure, and rebound.
The place to start is with your air pressure. The head angle of the bike will have a big influence on what pressure will be right for you. A closely related variable is the sag of the rear shock which affects head angle and the overall balance of the bike. The more raked out a frame is the lower the pressure will need to be in the fork because there is less weight directly over the front wheel and more friction on the bushings that the stanchions ride on (which creates more drag). The condition of the fork and which end of the go/no-go tolerances it was made to will also affect what air pressure you will need because these variables affect fork friction as well. What all this means is that there are no reliable air pressure charts or suggestions that I can give you based on weight alone.
But there is an easy way to find which air pressure is right for you. All you need to worry about at first is the fork sag, or ride height of the fork with you on the bike. You want to shoot for 25-30% of the fork’s travel being used as sag. For your 140mm travel 32 you will be looking for 35-42mm or 1 3/8″-1 5/8″. This sag should be measured using the sag o-ring that came on your fork. If you don’t have an o-ring just use a zip tie fastened around your stanchion. Once you have the air pressure where you think it needs to be, get on your bike and put your body in an attack position you would assume when going downhill that will get the fork to sag to the normal ride height. Then, gingerly get off the bike and measure the sag recorded by your o-ring or zip tie. Repeat the process until you get the sag where it should be.
With your air pressure set, it is time to move on to adjusting the rebound damping. For your rebound damping adjustment there is a wide range of usable settings therefore making it the hardest to set up right. Fast rebound is good for high speed trails with small high frequency bumps. Slow rebound is good for big drops. Keep these extremes in mind as you adjust your suspension. Just to get a feel for what the adjustment does, dial it all the way in and feel how slow it can go. Then dial it all the way out to see what a very expensive pogo stick feels like. Now find the middle point and start there.
From this middle point you can start to do some test riding of a section of trail that you know very well using a process called bracketing. After trying the middle setting down that section of trail, switch to a setting that is one click faster. Now, do it again with a setting that is two clicks slower. Eliminate either the slow or fast setting on your bracket and begin the process all over again using the winning setting. After doing this a couple of times it should be fairly obvious which setting is right for you.
In all likelihood, there will be two clicks that you like most and that you can’t quite choose between. Don’t worry, this is a good thing. Use the faster one for high-speed trails or on cold days when the oil in the damper doesn’t flow as well. Use the slower setting on trails with the big hits or on hot days where the oil is flowing a little quicker. Happy trails Nate!
Daniel Slusser is a professional bicycle mechanic with over ten years of experience. He holds a bachelor’s degree in business administration from HSU and a master’s degree in history from Cal Poly University. When he is not riding, wrenching, or writing he enjoys spending time with his wife and two children.