Basic Suspension Fork Adjustment
Suspension reduces the impact of bumps and uneven surfaces and gives the wheels better contact with the ground. On bicycles the front end is usually suspended by the use of a fork that has the suspension mechanism built into it.
Anatomy of a suspension fork:
- Steerer Tube-portion of the fork that goes through the frame
- Crown Race Seat-enlarged area of the steerer tube where the headset crown race is pressed on
- Cap-top of the hollow stanchion, can be a simple dust cap, a knob that adjusts compression or preload, or an air cap with a valve to add or relieve pressure from an air spring.
- Fork Crown-connects the stanchions to the each other and the steerer tube.
- Stanchion-stationary fork leg connected to the crown
- Brace or Brake Arch-spans the slider assembly from left to right, allows the slider to act as one piece and provides lateral stiffness
- Wiper, or Seal-prevents dirt or other contaminants from entering the fork
- Brake stud for linear pull brakes-provides a mounting point for rim brakes. May be eliminated on Disc only forks
- Slider-the lower fork assembly
- Drop-out-mounting area for the front wheel, or front axle
- Disc Brake Mount-mounting point for a hub brake. There are 2 main types of disc mount: IS (international standard) shown, or Post Mount. See the disc brake section of this document for more information
Basic Operation of a Suspension Fork A suspension fork reduces the impacts and vibrations of uneven riding surfaces by compressing or extending along its range of travel. The travel of a suspension fork is the distance the fork slider moves on the stanchions from fully extended to fully compressed. The movement of the fork is controlled by the spring, compression damping, and rebound damping. Suspension forks use a metal spring (coil spring), pressurized air in a chamber (air spring), or an elastomer (think of nerf football material) to return the fork to its normal position after activation. Compression damping controls how quickly the fork can move from its normal state to its compressed state. Many forks have adjustable compression damping; increase the compression damping and the fork will move more slowly, reduce compression damping and the fork will move faster. Rebound damping controls how quickly the fork can move from a compressed state to its normal state. Some forks have adjustable rebound damping: reduce the rebound damping and the fork will return quickly, increase the rebound damping and the fork will return more slowly.
Basic Suspension Fork Adjustment The effectiveness of a suspension fork is highly dependent on how well it is tuned to the rider's weight and riding preferences. Each fork is slightly different in how it is tuned and what adjustments can be made. Here are some general guidelines that can be applied to most forks: Set the Spring Preload- the preload adjusts how much the fork is compressed when the rider is in a normal riding position. This amount of compression is known as sag. Sag allows the suspension to extend to keep the wheel in contact with the riding surface in the case of a hole or depression. See the owners manual of the fork for the suggested sag for a given fork, otherwise a good starting point for most forks is to be about 25% compressed when the rider is seated on the bicycle.
To set the pre-load on a fork:
- Turn the compression and rebound damping as low as they will go
- Loosely attach a zip tie to one of the stanchions so it will barely stay in place on the stanchion
- Move the zip tie all the way down so it is against the wiper seal
- If your fork manual does not specify the range of motion for your fork follow these steps:
- fully compress the fork by applying body weight, you should feel the fork bottom out
- if the fork does not bottom out reduce the pre-load and try again
- measure the distance from the top of the wiper seal to the bottom of the zip tie
- write this distance down so you do not forget it.
- Find a wall to lean against or a strong friend to help support you and your bike, gently get on the bicycle and sit on the saddle with your hands on the handlebars just like when you are riding. Try not to compress the fork while getting on, just once you are seated.
- Dismount the bike and measure the distance from the top of the wiper seal to the bottom of the zip tie. This is the amount of sag
- Multiply the range of motion measurement from your manual or from step 4 by .25. This is the suggested sag
- If the suggested sag is greater than the measured sag, decrease the spring pre-load. If the suggested sag is less than measured sag, increase the spring pre-load.
Adjust the Rebound Damping-since the rebound damping controls how quickly the fork extends it must be adjusted so that the fork will be recovered in time for the next bump or hole. Many stock forks or entry level forks will not have a separate rebound damping setting. On adjustable forks good initial test is to push down on the fork while standing still, and then release it quickly and check that the rebound rate just about keeps up with your hands when you release the pressure. Otherwise rebound damping is adjusted to suit the rider and the trail conditions. Rebound damping that is set too high will cause the fork to "pack" or "stack" where the fork has not recovered from the previous impact before the next one comes. Rebound damping set too low will cause the fork to jump back or jump up into the rider after a big impact.
Adjust the Compression Damping-properly adjusted compression damping prevents the fork from bottoming out when compensating for a large impact. The best way to set the compression damping is by riding. Follow the instructions in the fork owners manual for initial settings, otherwise start with the knob set about half way between minimum and maximum. Ride a test loop with some moderate and large bumps. If it is set too low the fork will bottom very easily. If the damping is set too high the fork will not compress very far even on large impacts and more shock will be transmitted to the riders arms and shoulders.