How-To: Mountain Bike Suspension Set Up with Art's Cyclery
Besides having air in your tires, there is nothing more crucial to enjoying your time on the bike than proper suspension set-up.
The first step is to determine sag; the distance your bike settles into its travel when weighted. Verify that your fork and shock have travel indicators, or O-rings around a fork stanchion and shock shaft. If there are none, install a zip-tie yourself, but not too tightly.
Let’s start with the shock. Place the bike next to a wall or have a friend hold the bike while you climb aboard. Wear what you would on a ride, including filled hydration pack, armor, and such. Stand on your pedals in the attack position, centering your weight over the bike. Gently bounce a few times, then slowly reach down and push the travel indicator up against the shock body, without compressing the shock. Slowly dismount the bike, moving forward, so you don’t compress the shock. With your air spring pressure set properly, your travel indicator should move 20-30% of the shock stroke, or exposed shock stanchion. Longer travel bikes need slightly more sag, usually around 35%. Increase or decrease air pressure five PSI at a time until proper sag is achieved. Write down the air pressure figure that it took to reach the proper sag point for your bike.
For a coil shock, unscrew the shock preload collar all the way, and retighten just to the point where you feel resistance from the spring. Now measure the uncompressed eye-to-eye shock length. Then, subtract the compressed eye-to-eye length, and you’ll have your sag. You will need a helper to measure the compressed shock length. Divide the sag measurement by the total shock stroke for sag percentage. If you’re not getting enough sag, you’ll need a lighter spring. If you have too much sag, tighten the coil spring preload collar and repeat. Keep going until you achieve optimal sag for your bike. If you need more than two-to-three full turns (depending on manufacturer) to reach optimal sag, you’ll need a stiffer spring.
Setting sag on your fork follows the air shock procedure, comparing the total exposed stanchion to the amount the travel indicator moves. Be sure to dismount the bike rearward so as not to compress the fork.
Now that we’ve got our spring rates dialed in, it’s time to set rebound damping. Less damping—turning the adjuster counter clockwise— means the shock or fork will return from compression faster, and vice-versa. If rebound is too fast, you’ll get a skittish, bucking ride. Too slow, and your suspension won’t be ready for the next impact, giving a harsh ride.
The easiest way to get in the ballpark is to use the “top-out test,” which can be performed on the shock and fork. Turn your rebound adjust knob so it is fully open. Now compress the shock as much as possible by pushing down on the saddle, and quickly let go. If the shock extends too quickly, coming to an abrupt stop at the top of its travel, you’ll need to increase damping (tighten the adjuster) to slow it down. You may also be able to feel or hear the shock top out. Repeat the process until the shock no longer springs back harshly. Write down how many clicks you tightened the adjuster.
Another method is to ride off a curb while standing, gradually increasing rebound damping until your shock compresses and returns without bouncing. Repeat the top-out process on your fork, pressing down on the handlebars instead of the saddle. You will most likely need to fine-tune your rebound one or two more clicks on the trail. If the front or rear of the bike bucks or seems jumpy, increase the appropriate damping a click to slow the rebound down. If the bike seems like it’s overly harsh through successive hits, speed up the rebound a click so the suspension will be able to extend for the next impact. When you get home, write down your changes. It’s best to err on the slow side of rebound for the shock so you won’t get bucked, and on the fast side for the fork, so it won’t pack up and throw you forward. A general guideline is to set up your rebound 1 or 2 clicks faster for trails with small, high frequency bumps and 1 or 2 clicks slower for trails with big hits.
Compression damping adjustments are more involved, and require time on the trail to dial in. Not all suspension components feature compression adjustments. Most trail components offer low-speed adjustment, and DH components offer separate high and low-speed adjustability. Speed refers to the how fast the damper shaft is travelling, so high-speed compression handles big, square-edged hits and bottom outs, while low-speed compression affects small bumps and pedaling “platform,” along with brake dive and ride height in corners. It’s helpful to think of low-speed damping as a blow-off gateway to access the high-speed damping.
My favorite way to set up compression damping is to back the damping all the way off—loosen the adjuster knob—and get out on the trail, paying attention to specific ride characteristics, which apply to both the fork and the shock. First, if you find yourself bottoming out harshly or too often, increase high-speed compression damping by tightening the adjuster knob. Adding volume reducers to your fork and/or shock’s air chamber is another option to deal with this problem. This will increase the spring rate at the very end of the travel, possibly preventing bottom out. If you get to the point in your testing where you are never using all the travel, and the bike feels harsh, decrease high-speed compression damping.
For low-speed damping adjustment, focus on brake dive and ride height as an indicator of your fork’s low-speed compression. If the fork compresses excessively when braking, or when driving through turns, increase low-speed compression damping until ride height remains stable and brake dive is under control. For your rear shock, small bump compliance and pedal bob will direct you in adjusting your shock’s low-speed compression. If your shock is not absorbing small bumps try decreasing low-speed damping. Increasing low-speed compression damping may help to reduce pedal bounce.
It’s important to record all your suspension settings. This lets you see how changes affect your bike’s behavior, and will get you back to the sweet spot if your settings are altered. Once you finalize your settings, you might write them on pieces of tape affixed to your fork and shock so you’ll always know where you should be.