Bicycle Glossary

ALLEN BOLT -- A threaded bolt with a hexagonal depression in the center of its head.

ALLEN KEY -- Hexagonal tool that fits Allen bolts.

BEARING -- A mechanism that usually consists of a number of ball bearings and circular channels, or races. It allows two metal surfaces to move freely while in contact.

BLOCK -- Cogs fitted to a FREEWHEEL.

BOSS -- Threaded metal fixture on a bicycle frame to which an item such as a bottle cage or a pannier rack is attached.

BOTTOM BRACKET -- Rotating unit that connects the CRANKARMS.

BOTTOM OUT -- A word that describes the point when a SUSPENSION fork or shock absorber reaches the limit of its travel.

BRAKE-LEVER HOOD -- The body in which the brake lever sits, connecting it to the handlebar.

BRAKE TRAVEL -- The distance a brake lever moves before the brake pads engage the braking surface on the rim or hub of a wheel.

CABLE CRIMP -- A small metal cylinder that is closed at one end and fits over the cut ends of a cable to prevent fraying.

CASSETTE -- A collection of cogs that fit on the rear wheel's FREEHUB.

CHAINRING -- A toothed ring attached to the CRANKARMS that drives the chain and, in turn, the cogs and the rear wheel of a bicycle.

CHAINSTAY -- The frame tube joining the BOTTOM BRACKET shell and rear dropout.

CRANKSET The assembly of CHAINRINGS and CRANKARMS.

CLEAT -- A plastic or metal plate that fits on the sole of a cycling shoe and engages with a CLIPLESS PEDAL to hold the foot on the pedal.

CLIPLESS PEDAL -- A pedal with a mechanism to engage the cleat on the sole of a cycling shoe and hold it securely in place. Called clipless because they replaced pedals that had toe clips and straps.

COG -- A circular metal object with teeth that is turned by the chain. Combined with other cogs, it forms a CASSETTE or BLOCK. Cogs are sometimes called "sprockets."

COMPRESSION -- The action of a suspension system when it absorbs an impact from the terrain. The term refers to the compression of the spring.

CRANKARM -- The lever that joins the pedals to the CHAINRINGS and transfers energy from the rider's legs to the DRIVETRAIN of the bike.

DAMPING -- The process that absorbs the energy of an impact transmitted through a suspension system. It controls the speed at which any form of suspension responds to uneven terrain.

DERAILLEUR -- Device that pushes the chain onto a larger or smaller CHAINRING or cog. See also Derailleur gears.

DERAILLEUR GEARS -- A system that shifts the chain between COGS on the rear wheel (rear derailleur) and between CHAINRINGS attached to CRANKARMS (front derailleur); it allows multiple gearing on bikes.

DOWN TUBE -- The frame tube that joins the bottom-bracket shell to the head tube.

DRIVETRAIN -- The assembly of pedals, CRANKSET, chain, and cogs that drives the bike forward by converting the rider's leg power into wheel rotation.

DROPOUT -- A slotted plate at the end of the fork blades and stays, into which the axle of a wheel is attached.

EXPANDER BOLT -- A bolt that draws up a truncated cone or triangle of metal inside a metal tube in order to wedge the tube in place. Commonly found inside the stem of a threaded headset.

FREEHUB -- A mechanism, part of the hub, that allows the rear wheel to rotate while the pedals remain stationary.

FREEWHEEL -- A mechanism that does the same job as a FREEHUB but can be screwed on or off the hub.

GEAR -- An expression of the CHAINRING and cog combination, linked by the chain, that propels the bike.

GEAR-SHIFT LEVER -- The control mechanism, usually on the handlebar, used to initiate gear-shifts.

GRUB SCREW -- A headless, threaded bolt that has a single diameter throughout its length.

HEADSET -- The bearing unit that attaches the forks to a frame and allows them to turn. There are two varieties: threaded and threadless.

HEAD TUBE -- The frame tube through which the steerer tube runs.

HEXAGONAL BOLT OR NUT -- A threaded bolt with a hexagonal head, or a hexagonal nut that fits onto a threaded bolt.

HYDRAULIC -- A type of mechanical system that uses compressed fluid to move an object.

LOCKRING/LOCKNUT -- A ring or nut used to tighten onto a threaded object and lock it in place.

NEGATIVE SPRING -- A device that works against the main spring in a suspension system. In compression, for example, a negative spring works to extend the fork, helping to overcome the effects of STICTION.

NIPPLE -- The piece of metal attached to the end of a cable that secures the cable in the control lever.

Non-Recreational Biking -- Any time a bicycle is used for utilitarian and/or transportational purposes, such as commuting, shopping, running errands, etc. Said another way, non-recreational biking is when the bicycle is used as a realistic alternative to automobile transportation. This does not mean you can't simultaneously have fun or get a good workout!

PLAY -- A term describing any looseness in mechanical parts.

QUICK-RELEASE MECHANISM -- A lever connected to a skewer that locks or releases a component from the frame.

REBOUND -- A term to describe the action of a suspension system after it absorbs an impact from the terrain. It refers to the extension of the system's spring.

Recreational Biking -- When a bicycle is used strictly for leisurely riding, mountain biking, racing, exercising or other athletic use.

SEAT POST -- A hollow tube that holds the saddle and is inserted into the seat tube.

SEAT STAY -- The frame tube joining the bottom bracket shell and rear dropout.

SEAT TUBE -- The frame tube that holds the seat post.

SIDEWALL -- Part of the tire between the tread and rim.

STEERER TUBE -- The tube that connects the fork to the stem and handlebar.

STEM -- The component that connects the handlebar to the steerer tube.

STICTION -- A combination of the words "static" and "friction." It describes the tension between moving and static parts at rest, such as the seals and stanchions in a suspension fork.

STOPPER PIN -- The end of a cantilever or V-brake return spring that fits into a locating hole on the bike's brake-mounting bosses.

SUSPENSION -- An air/oil or coil/oil system that absorbs the bumps from a trail or road. The system is either integrated into the fork or connected to the rear wheel via a linkage.

THREADS -- The spiral grooves cut into metal that allow separate parts to be screwed or bolted together.

TOP TUBE -- The frame tube that joins the seat tube to the head tube.

TRAVEL -- A term that refers to the total distance a component moves in carrying out its purpose. For example, travel in a suspension fork is the total distance the fork has available to move in order to absorb a shock. Brake travel is the distance a brake lever must be pulled before the brakes fully contact the braking surface.

TREAD -- The central part of a tire that makes contact with the ground.

VISCOSITY -- A rating system for oils, which also refers to the weight. A light oil has low viscosity and moves more quickly than a heavy oil through a given damping mechanism. This results in a faster-acting suspension system or reduced damping.

WHEEL JIG -- A stand that holds a wheel so that its rim runs between two jaws. Used in truing a wheel after replacing a broken spoke.