Suspension Setup Guide
Suspension on your mountain bike is pretty magical when it’s all properly set up. You can always stop in at the shop for a quick check of your bike's sag and damping adjustments. For those of you who like to get fully involved with your own setup and maintenance, though, we’ll try to break down the basic principles for you here in plain English.
Most forks and rear shocks on mountain bikes today are air sprung. Coils are still in regular use for downhill racing and really extreme conditions, but air is king for just about everything else. Air shocks are lighter and more adjustable and every bit as durable in all but the harshest conditions.
There are a couple of common mistakes and misconceptions with air springs, so let’s start by getting those out of your head.
It’s a common misconception that an air shock loses air when you remove the pump from the valve. If you’re using a proper suspension pump, this is 100% FALSE. Suspension pumps have a specially designed chuck and air seal that lets the shock’s valve core close fully before the seal disengages. The hiss you hear is only air loss from the pump’s hose. When you put the pump back onto the shock, the gauge reads lower because air from the shock backfills into the hose.
Setting Air Pressure...Twice
To improve small bump sensitivity and give air sprung shocks and forks a smoother, more linear spring rate, there’s a small bypass that lets air from the main spring chamber fill in behind the piston, too. Think of it as using some of the air you put in to create a light, reverse spring working with you to help the suspension compress more smoothly through the first few millimeters of travel.
When you pump up, a significant amount of that air might be wanted by this secondary chamber. Air up the main chamber just like you expect, but before removing the pump, push down to cycle the fork/shock a half dozen times or so. Look at the gauge on the pump and top it up if the reading has gone down. Repeat this until you see no change in the gauge reading.
This is the basic starting point for suspension setup. Sag refers to the amount your fork or shock compresses when you get on your bike and sit still. Usually expressed as a percentage of your total available fork or shock stroke, sag is usually in the neighborhood of 25% to 30%. There’s always a little room within this range for experimentation and personal taste, so don’t be afraid to play around a bit.
Typically, cross country race and other short travel bikes will be set up at the lower end of the sag scale, and long travel trail bikes on the higher end. So if you ride a 100mm travel Specialized Epic, you’ll probably want about 25mm (25%) of sag on the fork. On a 150mm travel Santa Cruz Hightower LT, something more like 45mm (30%).
The rear shock is a little less obvious. Remember that sag is a percentage of your shock’s stroke. A bike with 150mm of rear wheel travel usually has a shock with something around 51mm of stroke. Some shock bodies have a scale printed on them, but if yours doesn’t, measure the exposed part of the small end of your shock and then set your sag to the appropriate percentage of that. So a 51mm stroke shock for a 150mm travel bike would be sagged in somewhere around 15~16mm.
First off, it’s damping, not dampening. Dampening is something you can do with a wet rag. Rebound damping slows the return speed of your spring so your wheels don’t bounce wildly through rock gardens and so your bike doesn’t try to buck you off after a hard landing. Compression damping slows the spring compression and is generally used on bicycles to resist “pedal bob,” the tendency for the bike to want so squat beneath you under pedaling load. “Lockout” on most forks and shocks is really just a very firm compression damping setting.
Adjusting your bike’s damping seems a little mysterious until you have some experience with it. Generally, you’ll want to start with compression damping in it’s most open setting (usually turned all the way counter-clockwise) so you can focus on what the rebound is doing first. Rebound speed is largely a matter of personal preference, so the next part will take some experimentation. Start with your riding style. If you’re a cross country or the sort of trail rider who generally tries to keep both wheels on the ground, a quicker rebound speed will generally work well. If you like to send it, slower rebound will probably work better for you.
With this in mind, find a familiar section of trail that sums up the sort of terrain you spend most of your time on. Ride it. Over and over. Pay attention to the sound of your bike. Pay attention to pedal strikes. If your bike feels or sounds overly chattery, your rebound may be too quick. Turn your rebound adjuster a couple clicks clockwise. If it feels sluggish or if you’re hitting your pedals where you think you shouldn’t, your rebound might be too slow. Turn the adjuster a couple clicks counter-clockwise.
Once you’re happy enough with rebound, you can set compression damping. It’s pretty much the same process, but most people have an easier time with this part. If you ride fast, buff trails all the time, you’ll want a lot of compression damping. If you ride where we ride, with lots of rock gardens and stutter bumps and rooty singletrack, you’ll probably want less compression damping. Most forks and shocks even keep the compression damping knob easily accessible so you can quickly change things on the fly as the trail goes through its moods.
You’ll be making these trips several times before you really nail it, and it’s entirely likely that you’ll second guess yourself and go through this process again and again until you’re sure you’re happy. It’s perfectly normal and we all go through it with a new bike. Some riders get so into the process that they even keep a journal of suspension settings and notes about the ride so they can compare performance and make adjustments specific to the trail. Most of us, though, are completely happy with finding something pretty good and sticking with that everywhere.