 |
|
Anti-Dive A Mechanical or Hydraulic device intended to decrease the amount the front end dives under braking. The hydraulic types are varied in design but all increase the compression damping when the brakes are applied. Most are actuated by the braking force on the wheel cylinders or the hydraulic pressure in the brake lines. Quite common on large bikes in the 80's they are rare now because they create even more harshness on the square-edge bumps. Still used on Gold Wings through at least 2005. 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 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.
Bottom-Out Bumper A rubber or urethane bumper commonly used in shocks to cushion the shock when it uses up all the travel on compression. Typically made out of rubber or urethane. They typically break down after a while and should be replaced.
Bottoming Cone A hydraulic device designed to give an additional damping resistance when the fork or shock reaches bottoming. Cartridge Fork A more sophisticated type of fork than a Damping Rod Fork that typically utilizes pistons with shims that bend 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 poorly designed cartridge forks create very similar curves to damping rod forks.
Chassis The frame, swingarm, forks, shock, linkage and wheels. If the motor is a stressed member it can be considered as well.
Check 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 and therefore counted as clicks or quarter turns "out" (counter clockwise).
Compression Bolt Assembly The complete compression valve assembly. Also known as the Base Valve in a cartridge fork.
Cylinder Valve An additional compression damping circuit located at the top of the cartridge on some 1998 KYB dirt bike forks. Damper See shock absorber
Damping Circuit A physical path for suspension fluid that creates resistance. There may be five or more compression 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 The force created by a liquid moving through valving. KEY POINTS - Damping is velocity sensitive and converts mechanical energy into heat.
Damping Piston The valve that the shims are stacked on. It is sealed on its outer diameter with a piston ring. The piston ring is 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 utilized 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 excessively progressive resulting in harshness and bottoming.
Delta Valve An aftermarket fork valve that has externally adjustable Low Speed and High Speed Compression Damping. Used on dirt bikes. Fork Bushing A low friction load bearing sleeve. Modern Fork Bushings consist of a steel band with a coating of bronze and a layer of Teflon bonded on it. Most forks require two per leg. Early telescopic forks did not have these bushings and therefore suffered from even more friction than current designs.
- Inner Bushing Also known as a "RU" bushing. It fits onto the inner chrome fork tube and has Teflon on the outer surface.
- Outer Bushing Also known as a "DU" bushing. It fits onto the outer fork tube and has Teflon on its inner surface. Nitrogen An inert gas used to pressurize shock absorbers to eliminate cavitation. Argon or any inert gas could also be used. Offset A distance between two centerlines. On a motorcycle it typically refers to Triple Clamp, Axle, or Total Offset.
- 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.
- 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).
- Total Offset Triple Clamp Offset + Axle Offset = Total Offset
Offset Forks An external fork design that has the axle offset from the centerline of the fork. Commonly used on dirt bikes.
Orifice A hole. Commonly used as a "bleed" in shocks and cartridge forks. It is typically used as the major source of damping in damping rod style forks. Orifices create "velocity squared" style Force vs. Velocity curves. In other words when the velocity is doubled the damping force increases with the square of the velocity, it increases by four times. This is the most progressive type of damping found in standard shocks and forks. Not necessarily round. PDS Position sensitive Damping System. A position sensitive damping system developed by WP for KTM starting in 1998 for the chassis with no linkage (the shock bolts directly from the frame to the swingarm, therefore the Leverage Ratio Curve is not very progressive. NOTE: Requires a progressively wound spring.
Piston Ring A sealing ring on a shock piston or a cartridge fork rebound piston. Usually made of a Teflon composite or a Teflon coated steel band. It seals with pressure behind it similar to the piston ring in a motor.
Piston Ring Energizer O-Ring The o-ring underneath the piston ring that provides an initial load against the inner wall of the shock body.
Piston Rod a.k.a. Damping Rod or Rebound Rod. The rod in a cartridge fork attaches to the fork cap and usually caries the rebound piston as well.
Preload Adjuster A method of adjusting the preload externally. These can be ramped, threaded or hydraulic. Hydraulic preload adjusters on shocks allow remote adjustment of the preload. NOTE: When the preload adjusters are backed off all the way they do not necessarily have zero preload. Particularly in forks there is usually some preload at the minimum external preload setting.
Preload Spacer Material used to set the preload in a fork. 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 a steel washer is used on both ends of the spacer. Rebound Rod a.k.a. Damping rod in a cartridge fork
Reservoir A canister or portion of a shock absorber with a membrane or piston separating the fluid from a compressible gas. Usually filled with high-pressure nitrogen. This allows for displacement of the fluid by the shock shaft since oil is incompressible.
- Piston Reservoir A style of reservoir where the fluid and the nitrogen are separated by a floating piston.
- Bladder Reservoir A style of reservoir where the fluid and the nitrogen are separated by a flexible membrane. Shim a.k.a. valving shim. A thin washer made out of spring steel used in a damper to create hydraulic resistance. It is typically stacked up in combination with other shims of various thickness and diameters on a damping piston to create the required damping curve.
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 reaches bottoming.
Shock Linkage A series of mechanical levers designed to change the leverage the wheel has on the shock as it goes through its travel.
Shock Shaft The main shaft in a shock absorber. The valving is on one end and the eyelet is attached to the other. It is typically hard chrome plated for durability.
Spring A mechanical device that stores energy as it is displaced. It usually is in the form of a coil design but sometimes is a leaf spring. Typically chrome silicon steel is used but titanium and carbon fiber have been used. Air can also be used as a spring. KEY POINTS - Springs are position sensitive and store energy.
Suspension Fluid Used inside a shock absorber for two purposes. 1) To create damping when forced through orifices or valving and 2) To lubricate. Viscosity and Viscosity Index are important quantities. KEY POINT - Oil is incompressible. Top-Out Bumper A rubber or urethane bumper commonly used in shocks to cushion the shock when it comes to full extension.
Top-Out Spring A coil spring commonly used in forks (and some shocks - see anti-high side device) to cushion the fork when it comes to full extension.
Top-Out Valve A hydraulic top-out device.
Trail The distance the Wheel Contact Point is behind the Steering Axis at Ground Contact. Or a nice place to ride on the weekend.
Twin-Chamber Fork A cartridge fork with the cartridge inverted so the compression is at the top. This requires a reservoir. The oil inside the cartridge does not mix with the oil on the outside of the cartridge. This means there are two distinct "chambers". Showa popularized this design, however it is currently being produced by KYB and Marzocchi as well. Valving The mechanical hardware that creates damping. This can be a combination of holes, ports, shims, springs, check valves, etc.
Viscosity The resistance to flow (more accurately the resistance to shear) of an oil. Commonly called the "thickness" of the oil.
Viscosity Index (VI) A number that represents the viscosity stability of the oil with respect to temperature. How much it thins out when it heats up. The higher the number the more temperature stable it is. Base mineral oils are about VI 100. |
