Glossary

A glossary of bicycle and bicycle parts and their functions.

Aero Wheel

A wheel designed with reduced wind resistance.See also: Air pressure

Air pressure

The amount of compression of the air in a bike tire. The tire pressure reduces the rolling resistance, and provides suspension to the bike, increasing the comfort of the ride. In the U.S. pressure is usually measured in pounds per square inch (psi). The typical modern fat tire rates at a pressure of up to 65 psi. The typical thin tire rates up to 100 pounds per square inch. The exact recommended pressure varies from one model of tire to another, and is typically imprinted on the side of the tire. The European air pressure measurement is expressed in “bars.” This refers to multiples of standard barometric pressure. See also: Aero Wheel

Bead

On a clincher type tire, the beads are the two metal or fiber hoops that hold the tire to the rim and provide a sealing edge against the rim.

Blowout

A bursting of a tire and inner tube., usually associated with a loud popping noise. This can be caused by filling a tire past the recommended air pressure, filling a tire that is mounted incorrectly or that is damaged, and can happen while riding and hit an large obstacle or sharp object. A blowout will typically necessitate a replacement of the tire and inner tube.

Cassette

A group of sprockets designed to be used with a freehub.

Clincher

A tire type that has a pair of “beads,” hoops that hold the tire to the rim by fit and air pressure inside a separate inner tube. This is the most common type of bicycle tire.

Derailleur

The assembly that "derails" or moves the chain from one sprocket to another, in order to change gears.

Dish

rear wheel hubs are often offset to allow for the freewheel assembly. Aka: "wheel dish."

Double butted spokes

Swaged spokes. The spokes are thicker at the ends than in the middle.

Dropouts

The slots in the frame and fork in which the rear and front wheels, respectively, are mounted.

Flanges

the outer edge of a wheel hub to which the spokes are attached.

Flat spot

as applied to tires or bicycle wheels, refers to a condition in a tire or wheel is not precisely round. With a tire, it may be mounted improperly, the incorrect size, or be of poor quality or damaged. Flat spots in bicycle wheels can be caused by hitting an obstruction, or from maladjustment of spokes.

Foldable tire

A clincher tire with non-metallic (Kevlar, plastic or fiberglass) beads. This type of clincher tire can be folded for storage. Aka. Folding tire.

Freehub

A wheel hub with a built-in freewheel.

Freewheel

The ratchet mechanism that allows the rear wheel to turn without turning the crank. Necessary to allow coasting. It can be part of the hub or part of the freewheel cluster, depending on the design.

Gumwall tires

Tires that have a natural gum rubber sidewall, or a synthetic sidewall that resembles gum rubber. When flexed, these sidewalls return with more energy than the typical black tire rubber, offering a more efficient ride.

Hub

The center of a wheel, containing an axle and bearings. Rear hubs are attached to a subassembly of various types that is then driven by the chain. Rear hubs may include additional functionality, such as a planetary gear set or a coaster brake.

Inner tube

The air bladder which hold the air pressure within the tire of the bicycle. The tire provide the structure and protection, while the inner tube maintains the air pressure.

Kink

Damage in the form of a bend or dent in a bicycle rim. Typically caused by hitting a solid obstacle. Can possibly be repaired depending on the type of rim, and the extent of the damage.

Nipple

A spoke nipple.

Patch kit

A selection of tools and materials that allows the repair of bicycle inner tubes.

Planetary gearing

A system which provides two or more gearings in the rear wheel hub, or rarely, into the bottom bracket.

Pre-stressing

A newly built wheel typically needs tensioned, stress-relieved, then re-trued to provide a stable, solid ride.

Presta valve

A type of air fill valve used on high-pressure bicycle tires. It is thinner than Schrader-type valves.

Puncture

A hole or leak in the inner tube, causing loss of air pressure. The result is a flat tire.

Quick-release

A device typically used in place of a static bolt allowing for easy tool free removal or adjustment of a component. Frequently used on wheel hubs and seat posts.

Quick-release brakes

Brake calipers that can be opened easily to allow dismounting a tire.

Rim

The metal hoop which holds the tire and tube, which is attached to the hub by spokes.

Rim strip

A strip of rubber, plastic or cloth used in clincher type rims that protect the inner tube from being punctured by wear against the tops of the spoke nipples or the rim.

Rolling a tire

A situation in which a tubular tire can roll off the edge of the rim while cornering. These tires are glued to rims that are not as concave on their outer surface as conventional rims. Rolling a tire is usually caused by improper gluing, but can happen in unusual cornering situations, such as hitting a stone or edge in the pavement while cornering. With properly glued tubular tires, rolling a tire is not common.

Schrader valve

A type of air fill valve used on automobile and bicycle tires. See presta valve

Seating

The way a tire is mounted on a rim. A properly seated tire will be nicely round producing a smooth ride. An improperly seated tire can have bulges of flat spots, and can even blow out if very poorly seated.

Sew-up tire

A tubular tire.

Skewer

The portion of a wheel quick-release mechanism that extends through the hub axle.

Snakebite flat

A flat tire caused by pinching the tire and tube between the rim sidewalls and a rock or other obstruction. It usually causes two parallel punctures in the tube that look like a snake bite.

Spoke fatigue

A condition in which spokes have reached their maximum life span. This is affected by the stressing and de-stressing that occurs with every revolution of the wheel. The metals of the spokes begin to develop stress fractures which eventually lead to failure of the spoke. This usually only becomes a problem with wheels that have been in use for a great number of miles.

Spoke key

A small wrench for adjusting spoke tension by turning the nipple. Also called a spoke wrench.

Spoke nipple

A long thin nut that fastens a spoke to the wheel rim. By turning the nipple, the spoke can be tightened or loosened, and by adjusting several spoke nipples, the wheel can be aligned.

Spoke nipple

A flanged nut that threads onto the end of a spoke attaching the spoke to the rim.

Spokes

Thin metal rods that hold wheels together. Spokes are used to attach the rim to the hub.

Suspension hub

A ruggedized hub designed to be used with a suspension, which induces more shock and work load to the hub.

Tire bead

On clincher tires, the metal, fiberglass, or plastic cable running along the edge of both sides of the tire, called the "bead." This is molded into the edges of the tire. The bead seals the tire against the rim once filled with air pressure, keeping the tire on the rim.

Tire lever

A tool for removing tubular tires from rims used to pry the tire over the edge of the rim.

Tire Liner -

A strip of rubber, plastic or cloth used in clincher type rims that protect the inner tube from being punctured by wear against the tops of the spoke nipples or the rim.

Truing a wheel

The process of making a wheel truly round by adjusting spoke tension.

Truing stand

A fixture for holding and measuring a wheel while it is being trued.

Tubular tire

A tubular tire takes the tube and the tire and combines them into one item that is then fit to the rim and glued in place. Tubulars don't have a bead. Instead, the edges of the tire are sewn together around the inner tube, and consequently, are also called “sew-ups.” These tires are fit to the wheel and attached by gluing the tire to the rim.

Valve

Bicycle inner tubes have valves through which air can be put into the wheels. The two common types of valves are Schrader valves, which are the same as the valves found on car tires, and Presta valves, which are smaller and lighter in weight.

Wheel

A complete rotating unit. A common bicycle wheel consists of a tire, inner tube, rim strip, rim, spokes and a hub. Other components may be built into the wheel that add functionality.

Wheel alignment

The condition of the roundness, and lateralness or planeness of a wheel. A properly aligned wheel will produce a smooth ride, free of wheel induced vibration, wobble or bounce.

Wheel truing

To align a wheel.

Wheelsmith

A bicycle professional who specializes in building and/or repairing wheels.

Work stand

A tool that holds a bicycle off the ground for convenient repair.