Glossary
In this page, I will try to explain the many terms and acronyms of the Mountain Biking world.
A guide to suspension terminology.
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ABP:
Trek’s acronym for Active Braking Pivot. ABP describes the pivot point between the swingarm and seatstay, designed to rotate concentric with the rear axle. In conjunction with the location of the suspension’s forward swingarm pivot and upper link, ABP decouples braking forces from the suspension action. So far, ABP is employed on the Select 2008 Fuel EX models and the Remedy.
Active suspension:
Refers to any suspension that remains uncoupled from braking and pedaling forces.
Air spring:
A compressed air chamber the replaces a conventional coil spring in a shock or fork.
Air volume:
A suspension term used to describe the type of spring rate that is expected from a given sized air spring. A low volume air spring tends to ramp up as it compresses rising rate. A high volume air spring tends to be stiffer at the beginning of the compression stroke and does not ramp up as much at full suspension.
Angular contact bearing:
Ball bearings that are designed to ride on special ground races. The balls contact the inner and outer races at an angle, which allows the bearing to handle thrust, side to side, loading. Most ball bearinggs are radial types, which are primarily designed to handle loads on a vertical plane, in line with the balls and races. Angular contact bearings are used in better quality suspension pivots and other key points that require 0 bearing play.
Anti-squat:
A common word used to describe any suspension device that prevents the rear of the bike from compressing, either under braking or due to acceleration forces.
Anti-dive:
Any device, usually a form of low speed hydraulic compression damping, that is used to prevent the fork from compressing under braking forces.
Asymmetrical:
Usually describes a swingarm with chainstays that are routed differently from the rear dropout to the bottom braket pivot junction to clear drivetrain items on the right side of the frame. Also means to a pivot or linkage that is offset to one side of the frame for clearance purposes.
ATA:
Marzocchi’s Air Travel is their most adjustable air sprung for system that offers 1.5 inches of travel adjustment and a positive and negative air spring system.
Axle path:
The invisible path that rear axle traces as the suspension moves through its travel. Axle path is important because it affects the way the suspension responds to bumps and can alter the distance between the axle and the crankset, which causes "chain growth" and "pedal feedback."
Bionicon:
A line of dual suspension bikes which uses an adjustable stroke air sprng fork that is plumbed into a small air cylinder inline with the shock. When the fork stroke is shortened, the eye to eye lenght of the shock is simultaneously lenghtened which rocks the frame forward and alters its steering and seat tube angles by over three degrees.
Big-hit:
Bicycle jargon for a sturdy, long travel dual suspension bike or riding style that includes very aggresive riding, jumping and impacting terrain features which constantly bottom out the suspension travel.
Bleed circuit:
A channel inside a hydraulic damper that allows some suspension fluid to bypass the rebound or compression valves. Bleed circuits are too small to pass significant volumes of fluid and thus are used to control low speed damping. Almost all external rebound and compression adjustments control bleed circuits.
Blow-off valve:
A spring loaded valve in the compression side of a hydraulic damper that protects the shock or fork from destruction by releasing fluid when internal pressure reaches safe levels. Blow off valves are employed most often in forks or shocks with a lock-out feature, but Specialized and Fox have used adjustable versions to moderate the effects of their inertia valve anti-bob systems.
Bob:
The tendency for a fork or rear suspension to rhythmically compress with each downward thrust on the pedals such as the Scott Equalizer shock, or with a combo of air volume and hydraulic compression damping used in the Fox DHX Air and Curnutt shocks.
Bottom-out:
When a shock or fork reaches the end of it’s travel usually in a sudden manner.
Bottoming compression:
A term that describes the internal valving or an external adjustment that controls the shock or fork’s resistance to bottoming out in the last stages of the compression stroke. This can be done with air volume adjustments, such as the Scott Equilizer shock, or with a conbination of air volume and hydraulic compression damping used in the Fox DHX Air and Curnutt shocks.
Bottom bracket pivot:
Usually the swingarm’s forward pivot location in the area of the bottom bracket (crank bearings). Some suspensions actually use a concentric bottom bracket pivot, such as the Haro VLS (Virtual Link System).
Brain Shock (fork):
A Specialized -coined term for its inertia-valve anti-bob fork and shock products. the inertia valve uses a spring-loaded mass which closes off the flow of shock fluid until a bump unseats it and allows the suspension to compress.
Brake jack:
When applying the brake, usually the rear brake, brake jacking causes the rear suspension to extend and lift the back of the bike - a negative suspension trait.
Braking bumps:
A metered series of small bumps usually found at the entrance to corners or leading edge of steep downhills. Braking bumps are created when a suspension or rolling wheel cannot respond to a bump at a given speed and frequency, and thus an oscillation is created. The tire bounces off the first bump and begins to create the second. Dragging the rear brake diminishes the response of the rear shock and thus aggravates the condition that makes them.
Burping:
A slang that describes when a shock is highly stressed, usually laterally (in bending), and momentarily losed air-spring pressure or leaks oil.
Caliper boss (caliper mount):
Either a flange with a pair of threaded holes or a pair of threaded posts used to attach a disc brake caliper to a frame or fork.
Cartridge damper:
A self-contained damping system, similar to a slender shock, that is inserted into fork. Cartridge dampers can be manufactured under stricter controls to increase reliability, are easier to service, and are lighter weight than damping systems which are assembled directly into the fork sliders. Marzocchi and Manitou use cartridge dampers throughout their fork lineups.
Chain growth:
A slightly misleading term that describes the action of suspensions with axle paths that move away from the bottom bracket as they compress. Exscessive chain growth can be felt as a counterclockwise tug on the crankset as the suspension compresses and the taut, upper side of the chain unrolls slack from the derailleur side. Some designers use a moderate amount of chain growth to firm up the suspension under power, because chain tension acts to resist the suspension in compression and this counteract bobbing.
Chain guide:
Any device, usually fixed to the bottom bracket, that encircles the crank’s chainring to preven the chain from deraillinig over rough terrain. Most are made from four parts: the boomerang is the mounting plate fixed to the frame; the bash guard is either a ring that bolts onto the outer sprocket location or a thick plastic plate below the chainrings; the lower roller guide which forces the chain to wrap around two thirds of the sprockets’s diameter; and an upper guide which can be a second roller or a derailleurcage type arrangement.
There are 3 standards for mountin chain guides: the bottom bracket mount is simply held in place by the right-side thread-in bearing cup; the ISCG (International Standard Chain Guide) uses 3 bolts on a 2-5/16-inch bolt circle (59.24mm); and the ISCG-05 uses 3 bolts on a larger-diameter, 2-7/8-inch (73mm) bolt circle.
Chatter bumps:
Any rapid series of small-to-moderate sized bumps that typically defeats bicycle suspension and causes the bike to skip over the ground similar in effect to braking bumps.
Clicker:
Any adjustment knob or lever that has an indexing detent. Typically, the low speed rebound and compression dials of a fork or shock are called "clickers".
Coil-over shock:
Any shock which uses a coil type spring.
Coil spring:
Any spiral wound spring, usually steel alloy or titanium. Coil springs are usually marked with 2 values: the first is the designated travel; the second is the spring rate in inch-pounds. For example, a 1.75 x 650 is for a 1-3/4 inch stroke shock, and the spring rate is 650 lbs for every inch the spring is compressed.
Compensating piston:
Also called an IFP (internal floating piston), it forms a moving barrier inside the damper between the suspension fluid and a compressed gas chamber. The compensating piston makes room for the extra volume of the damper shaft as the shock is compressed.
Compression damping:
Friction, usually hydraulic fluid forced through various valves, used to control the fork or shock’s rate of compression. The primary reason for compression damping is to slow the damper near the end of its stroke to prevent harsh bottoming (high speed compression), and to maintain a certain ride height for better cornering and braking (low speed compression).
Curnutt damper:
A patended, pneumatically controlled compression valve that is adjusted by manipulating the internal pressure of the damper’s compensating chamber. Perfected for bicycle use by Charles Curnutt Jr. and Brent Foes, the Curnutt shock effectively controls suspension bobbing, and its pressure-activated damping piston automatically ramps up to control bottoming as the shock is compressed.
Damping:
Force, usually hydraulic friction, used to dissipate the energy of an impact or subdue the rebound and compression speed of a fork or shock spring so the suspension will return to its preset ride height. Damping prevents oscillation which, in the case of suspension, is a condition where each successive impact adds energy to the spring until the suspension bounces uncontrolled between full compression and full extension.
Damper:
It is the schock body, the fork cartridge or the assembly inside the fork that contains the hydraulic damping mechanism (or air damper in the case of Cane Creek’s England shocks and fork replacement cartridges).
Damping curve:
The resistance generated by a damper throughout its stroke, expressed as a graph, form an S-shaped curve.
Default settings:
The manufacturer’s recommended spring pressure and damping values for a given rider. Many forks and some shocks have their default settings printed near the adjustment controls. The rest are available on the suspension maker’s websites or in the owner’s manual. It is worth your while to memorize your default settings, or write them down where you can access the information on the trail, so you won’t have to sweat it if an experimental setup turns sour.
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