One of the most important suspension settings is static sag-the amount your bike's suspension compresses when you sit on it. This method takes into account any stiction in the components. It's best to have two friends to help-one to hold the bike while the other one measures-while you (fully dressed in your riding gear) do the compressing.
First, extend the front suspension completely. Measure from the seal wiper to the triple clamp for a conventional fork, or to the axle clamp for an inverted fork. Call this number L1. Sit on your bike in a normal riding position (or racing crouch if you're track-bound), and have one helper steady the bike. Your second helper should push down on the fork, let it extend slowly and then re-measure as before. This number is L2.
Finally, the fork should be extended by hand, settled slowly, and re-measured. This figure is L3. Halfway between L2 and L3 is where your suspension would settle if there were no friction in the system. Static sag can be calculated as follows: sag=L1-(L3+L2)/2. Repeat this process to determine the rear sag-measuring from the axle to a point directly above on the frame for each of the numbers. If you have too much or too little sag, dial in more or less (respectively) preload as needed.
Axle Offset-the distance between the centerline of the fork tube and the center of the front axle on offset axle forks (mostly used on dirt bikes).
Base Plate-a thick washer or plate that the valving shims sit on.
Base Valve-the compression-valve assembly on cartridge forks or older-style "twin-tube" shocks.
Bladder/Diaphram-a flexible membrane separating the suspension fluid from the nitrogen in a shock absorber. Allows the shock to be pressurized to eliminate cavitation.
Bleed-a free flow orifice that allows fluid to pass easily at low flow-rates. It is usually the lowest-speed circuit.
Bottoming Cone-a hydraulic device designed to give additional damping resistance when the fork or shock reaches bottoming.
Cartridge Fork-a more sophisticated type of fork that utilizes pistons with bending shims to create compression and rebound damping. The basic design allows the manufacturer to produce a less progressive damping curve than a damping rod fork. Note: Some cartridge forks create very similar curves to a damping-rod fork.
Check Valve/Non Return Valve-a one-way valve that easily opens in one direction and shuts off completely in the other direction.
Clickers-external adjusters usually controlling low-speed rebound damping or low-speed compression damping on forks. On shocks, the clickers usually control low-speed rebound and high-speed compression damping. Many bikes have no clickers. Note: Some clickers don't click. Unless otherwise marked, most adjusters create maximum damping when they are screwed all the way "in" (clockwise).
Damping Circuits-a path of resistance for suspension fluid. There may be five or more com- pression circuits and three or more rebound circuits in a shock or cartridge fork. The effect of each circuit generally overlaps creating massive flexibility and sometimes complexity as well.
Damping Piston-the valve on which the shims are stacked. It is sealed on its outer diameter with a piston ring usually made of a Teflon composite if the piston is sliding in a chamber (as with a shock or the rebound piston on a cartridge fork). On a compression piston on a cartridge fork, it is stationary and therefore is sealed with an O-ring.
Damping Rod Fork-a simple type of fork that utilizes a tube with holes in it to create compression and rebound damping. The basic nature of creating damping by shoving fluid through holes produces a damping curve that is extremely progressive.
Fork Bushing-a low-friction, load-bearing sleeve. It is a steel band with a coating of bronze and a layer of Teflon on it. Most forks require two per leg. Nitrogen-an inert gas used to pressurize shock absorbers to eliminate cavitation. Argon or any inert gas could also be used. Piston Ring-a sealing ring on a shock piston or a cartridge-fork rebound piston. Usually made of a Teflon composite. It seals with pressure behind it, similar to the piston ring in a motor.
Piston Rod (damping rod or rebound rod)-the rod in a cartridge fork attaches to the fork cap and usually carries the rebound piston as well.
Preload Adjuster-a method of adjusting the preload externally. These can be ramped or threaded.
Preload Spacer-material used to adjust preload internally. Thin-wall steel or aluminum tubing is commonly used. Many aftermarket spring companies use PVC as spacer material which works fine if the ends are finished flat and square, and a flat washer is used on both ends of the spacer.
Reservoir-a canister or portion of a shock absorber with a compressible chamber usually filled with high- pressure nitrogen. This allows for displacement of the fluid by the shock shaft since oil is incompressible.
Shim (clamping shim)-The "last shim" in a valving stack, farthest away from the piston and closest to the base plate. All the other shims must bend on the clamping shim.
Shim (valving shim)-usually a thin, spring-steel washer used in a damper to create damping. When used in combination with other shims, it is referred to as "valving." It is located on a damping piston or base valve. Shock Absorber-a hydro-mechanical device that uses a fluid to create resistance. Key point: The damping force is sensitive to velocity. The mechanical energy is turned into heat.
Shock Body-the outer cylinder of the damping unit. Usually made of aluminum or steel.
Shock Bumper-a mechanical cushion made out of rubber or urethane, designed to give additional spring-type resistance when the fork or shock bottoms out.
Shock Linkage-a series of mechanical levers designed to change the leverage the wheel has on the shock as the swingarm pivots through its range of travel.
Shock Shaft-the hard, chrome-plated rod in a shock. The valving is attached to the internal end and the eyelet is attached to the external end.
Spring-a mechanical device, usually in the form of a coil, but sometimes as a leaf, torsion bar, or air. Springs have remarkable memory and therefore are position sensitive. As a result, springs store energy.
Suspension Fluid-used inside a shock absorber for two purposes: 1) To create damping when forced through orifices or valving; 2) to lubricate. The fluid must be incompressible.
Top-Out Bumper-a rubber or urethane bumper commonly used in shocks to cushion the shock when it reaches full extension.
Top-Out Spring-a coil spring commonly used in forks to cushion the fork when it reaches full extension.
Triple Clamp Offset-the distance between the centerline of the steering stem and the fork tube. The more the offset the less the trail for a given fork geometry. Usually measured in millimeters.
Valving-the mechanical hardware that creates damping. It is a combination of holes, ports, shims, springs, check valves, etc.