26 Inch Wheels – ISO 559 mm – 26 x (decimal) This is the size used on most mountain bikes. Generally, any tire where the width dimension is expressed as a decimal inch value will be the 559 mm size, such as 26 x 1.0, 26 x 1.5, 26 x 1.75, 26 x 1.95, etc.

650A - is 590 mm, a.k.a. 26 x 1 3/8″ (Mostly used on English 3-speeds .)

650B – is 584 mm, a.k.a. 26 x 1 1/2″ (Mostly used on French loaded touring bikes and tandems, but lately experiencing a bit of a revival.)

650C – is 571 mm, a.k.a. 26 x 1″ (Mostly used on time trial bikes and racing-type bikes for smaller riders.)

29er – or Twenty Nine. The so-called “29 inch” tire size is not actually a new size, it is just a new marketing term for 622 mm (700C) wheels with fat tires.

This size is probably a good option for taller riders for off-road use, compared with 559 mm (26 inch decimal) wheels. Larger diameter wheels don’t sink as far into holes so they will give a better ride in rough conditions.

For shorter riders, wheels this large will cause unfortunate compromises in frame geometry, so they’re probably not a good option for riders of short or medium height.

Axle – The shaft at the middle of a hub.
Axle set - A hub axle, plus the cones, nuts, and washers that attach to it.
Bead – A hoop, usually of heavy steel cable, that forms one edge of a tire. Sometimes made of Kevlar ®; for lightness and foldability.

Butted Spokes – Thicker at the ends (Butted spokes are also called “swaged”). The idea is to make the spoke stronger at the ends, where the stresses are greatest, and lighter in the long middle section, where stresses are less.

Campagnolo ® – The leading Italian maker of bicycle parts. Campagnolo invented the quick release.

Carbon fiber – Carbon filaments used with a resin, in a technology similar to fibreglass.

Cartridge Bearings – Bearings which are assembled in a modular unit, as opposed to cup-and-cone bearings, which may be disassembled down to the individual bearing balls for service.

Ceramic – Ceramic coated rims

Some aluminum rims are coated with a ceramic material primarily to improve wet weather braking, and to reduce rim wear that often results when rim brakes are used in muddy/wet conditions.

The ceramic is fairly brittle, and if the rim gets dented even a little bit, the ceramic can flake off. If this happens, the braking will become very rough as the rim grabs/releases at the damaged section.

Ceramic bearing balls

Most bearing balls are super-hard steel. Lately, some suppliers have been promoting very expensive bearings that use ceramic balls.

These are a silly gimmick, aimed at gullible cyclists with too much money. They have no real benefit in practical use on bicycles.

Clincher Tire – This is the normal type of tire, with a separate inner tube. The tire consists of two hoops called “beads“, made of steel or Kevlar cable, which are held together by cloth, usually nylon. The whole assembly is dipped in rubber, with thicker rubber applied in the tread area.

A clincher tire has a separate inner tube, which is basically a rubber balloon. This fits inside the tire, and the tire is mounted on the rim by lifting the beads over the edge of the rim. The middle of the rim makes a sort of valley, and while the tire is being installed, most of the bead can fit into this valley. This gives enought slack to allow the bead to be pushed or pulled over the edge of the rim, even though outside diameter of the rim is larger than the inside diameter of the bead.

Strictly speaking, the term “clincher” is slightly incorrect, as it applied to an obsolete style of tire which had ribs in the edges of the tire which fitted into grooves on the rim, where the tire was folded under the tube. The air pressure in the tube pressed the rib into the groove, and “clinched” the tire in place. People who are fussy about this prefer the term “wire-on.”

Cross Country – or xc. A style of mountain bike or riding. Fairly smooth and non technical terrain. Typically less extreme in nature.

Cup-and-Cone Bearing – Traditional bicycle ball bearings use cup-shaped races and cone-shaped races, with the bearing balls rolling between them. They come in pairs, either with two cones on the inside, held bewteen two cups, or, with two cups on the inside and two cones at the outside.

Cyclocross – A type of off-road race using bicycles that resemble road bikes. Cyclocross courses are very rough and muddy, and are designed to force the competitors to dismount and run with their bicycles several times per lap.

Cyclocross originated as a winter training activity for road racers, and originally was done on retired road bicycles, modified for off road use. Gradually, competitive pressures caused the development of purpose built cross bikes.

Dish – A bicycle wheel should have the rim centered directly in line with the frame. The fork ends are symmetrical with respect to the frame, and the hub axle locknuts (or equivalent surfaces) press against the insides of the dropouts.

Wheels should be built so that the rim is centered exactly between the axle ends on the hub. In the case of rear wheels, the spokes attach to flanges which are not symmetrical…the right flange is usually closer to the centerline than the left flange, to make room for the sprocket(s).

When rear wheels are built properly, the spokes on the right side are made tighter than those on the left side. This pulls the rim to the right, so that it is centered with respect to the axle (and to the frame.) Viewed edgewise, a rear wheel built this way resembles a dish, or bowl, since the left spokes form a broad cone, while the right spokes are nearly flat.

By extension, the term “dish” is used as a general synonym for accurate centering, even in the case of symmetrical wheels.

Dish Stick – A tool for checking the dish of a wheel. It has the form of a curved stick with an adjustable feeler near the middle. The two ends of the stick rest on the side of the rim, 180 degrees apart, and the feeler is adjusted to just touch the locknut or other locating surface at the axle end. The wheel is then inverted, and, if it is correctly “dished” the three points will all contact the corresponding points on the second side of the wheel.

Disc Brake – A hub brake, similar to an automotive disc brake, consiting of a disc which screws on to the hub and a caliper attached to the frame or fork which squeezes on the disc.

Double Butted Spokes – Spokes Butted at both ends.

Downhill – Downhill biking refers to racing downhill at high speeds over very rough, steep and technical terrain. Downhill bikes are designed specifically for going down hill not for pedaling up.

Dustcap – A thin metal, plastic or rubber shield that covers the bearing balls of a conventional cup-and-cone hub.

E.R.D. – Effective Rim Diameter. This is the rim diameter measured at the nipple seats in the spoke holes, plus the thickness of the two nipple heads. The E.R.D. is needed for calculating the correct spoke length.

Eyelet – A reinforcement in a spoke hole of a rim. Eyelets provide a wider bearing surface against the rim, making it less likely for the nipple to pull through the rim. They also provide a smoother surface for the nipples to turn against while they are being tightened.

Fixed Gear – A rear hub in which the sprocket is rigidly connected to the hub, without a freewheel.

Freehub – Shimano trademark for a rear hub in which the freewheel mechanism is built into the hub itself, rather than being part of the sprocket cluster. Most freehubs use a cassette of sprockets.

Freewheel – The mechanism that makes coasting possible. A ratchet mechanism that allows the rear sprocket(s) to drive the wheel when pedaled forward, but allows the wheel to turn forward independently even when the sprockets are not turning. In other words, the freewheel is the part which makes coasting possible.

Freeride – Freeride is both a riding style and class of mountain bike designed for free riding. They typically have greater suspension length (6” to 8” +). Freeriding is a style of mountain biking that involves riding over and off of stunts, drops and jumps. In recent years riders have progressed to incorporating in air tricks into their riding.

ISO – The International Organization for Standardization. This is an international agency that is active in trying to rationalize bicycle design to make parts interchange more easily among bicycles made in different countries. Most ISO standards are compatible with British standards.

Machined Rim Sidewalls – Aluminum rims are made as an extrusion, curved into a hoop and then connected together at the seam, usually opposite the valve hole.

The seam may be welded, or, in the case of a lighweight, hollow-section rim, it may be made by fitting a short metal pin into the hollow at each end. (This part is sometimes called a “biscuit.”)

The seam area is never exactly perfect, and there is commonly a very slight difference in the width of the rim at the seam. When a brand new rim is first used (with rim brakes) the brake may grab a wee bit harder as the seam passes through it, causing an annoying pulsation in the braking. Generally this goes away after a couple of hundred miles of use, as the brake shoes wear down the irregularity of the seam.

Sometime in the 1990s, Mavic introduced their “SUP ® ” rims (Soudé Usine Proces: Welded Machine Process.)

These rims are made with an extrusion slightly wider than normal, with extra thickness on the braking surfaces. They use a welded seam (not normally practical on a thin walled hollow-section rim) and then, after the seam is welded, the rim is placed on a special lathe where the excess material from the sidewalls is machined away uniformly.

Other companies have copied parts of this process, using machining on both welded- and pinned-joint rims. Rims with machined braking surfaces have two advantages:

• When building up the wheel, they can often be trued to greater accuracy than traditional rims.
• They give smooth braking even brand new, with no need for a break (brake) in period as with traditional rims.

There is a potential drawback to this type of rim though:

• If the alignment of the two ends is less than perfect at the weld, the machining process can leave part of the sidewall thinner than it was designed to be. This can cause the rim to wear out from braking friction locally sooner than it otherwise would.

Mavic – A major French manufacturer of parts. Mavic has long been one of the top manufacturers of high-quality rims. In the late ’80′s they started to branch out into other parts, including very well-received hubs and cranksets.

Park ® Tools – The leading U.S. manufacturer of special tools for the bicycle trade. They are located in St. Paul, Minnesota. They are on the Web at: www.parktool.com

Pawl – A spring-loaded part that engages a set of teeth when moving in one direction, but slides over them when moving in the other direction. The pawls in a freewheel make a ticking sound when a bicycle coasts. Most freewheels have two or three pawls.

Presta – The narrow valve used on most high-performance bicycles, and all tubulars. Also known as a “French valve”. The wider Schraeder (automotive style) valve is used on children’s bicycles and utility bicycles.

Quick-release Wheels – Quick Release wheels use a cam mechanism to allow the wheels to be removed quickly, and without any tools. This was invented in the 1920′s by Tullio Campagnolo, when he suffered a flat while racing over the Croce d’Aune pass in the Italian Alps. His frozen fingers were unable to loosen the wing nuts used to hold his wheels in place.

Radial spoking – The oldest and simplest of spoke patterns. The spokes run straight outward from the hub to the rim. This is called “direct” or “radial” spoking. This pattern is not well suited for transmitting the torque of pedaling, or of a hub brake, but is suitable for front wheels.

Rim – The outer metal hoop of a bicycle wheel. The rim does not include the spokes, nor the hub.

Rim Cut – A pinch flat, or the damage suffered by the tire sidewall from similar causes.

Schraeder – Standard automotive-style air valve. The other, skinny kind is called “Presta“.

Sealed bearings – A “sealed” bearing is one which has rubber or plastic gaskets to prevent the entry of dirt. In the bicycle industry, the term “sealed bearing” is often used colloquially to refer to a cartridge bearing. This can be confusing to a consumer who may think that a hub is a high-tech cartridge-bearing unit, when it is actually a normal cup-and-cone bearing with a plastic dust cap.

Sew-up – Tubular tire.

Shimano – The leading manufacturer of bicycle parts. Shimano has come to dominate the industry, and to have a near monopoly on many parts categories.

Singlespeed – While any bike that doesn’t have multiple gears is technically a “single speed” bike, current use of the joined word “singlespeed” generally refers to a bike with a one-speed freewheel and hand brakes.

Skewer – In a quick-release hub, the skewer is the shaft that runs through the middle of the hollow axle, and the associated hardware, in cluding the quick-release cam and the acorn nut.

Solid Axle – A plain hub axle, as opposed to a quick-release axle, which has a hole drilled through it for the quick-release skewer. A solid axle is secured to the frame by nuts.

Spoke – One of the wires connecting the rim to the hub of a bicycle wheel.

Spoke Patterns – Spoked wheels may be laced in several different patterns. Most wheels use the semi-tangent pattern, less common is “direct” or “radial” spoking. Some rear wheels are laced “half radial”.

There are also “novelty” or fad lacing patterns, including the crow’s foot and snowflake designs. These patterns are eye catching, but have no practical advantage.

Straight gauge spokes – Not butted.

Straight Spokes – Originally, spokes didn’t have the elbow, and they were straight from one end to the other. This required a special type of hub, which was harder to manufacture than conventional hubs. Straight spokes are also harder to lace up, and tend to revolve when the nipple is turned.

S.U.P. ® – Soudé Usine Proces, (Welded Machined Process) Mavic‘s name for their rims which have a welded seam, with the braking surfaces turned on a lathe after welding.

See also Machined Rim Sidewalls.

Taco – To bend a wheel so that it assumes a saddle shape. A Tacoed wheel is more than just out of true, it has bent far enough that the spokes have assumed a new equilibrium position and lost tension. Two spots, 180 degrees apart will be way off to the left, two other spots, halfway between, will be way off to the right. A tacoed wheel is also known as a “potato chipped” wheel.

Tensiometer – An instrument for measuring spoke tension.

Tire – People usually think that tires are made of rubber. This is understandable, because rubber is all that you can see.

A tire is actually made up of three parts:

1. The beads are two hoops of strong steel wire (or, sometimes Kevlar ®.)
2. The cords, cloth forming the body of the tire, woven between the two beads. Most modern tires use nylon cords.
3. The rubber, which covers all the other parts. The rubber on the part that contacts the road is thicker, and is called the tread.

A bicycle tire is not airtight by itself, so it uses an inner tube, which is basically a doughnut-shaped rubber balloon. The inner tube has a valve to allow you to blow it up.

Touring – In cycling circles a “tour” is a multi-day ride, which is not a competition or a timed event. See also touring bicycle.

Touring Bicycle – A touring bicycle is designed for comfort, durability, efficiency and, in most cases, load-carrying capacity.

Triple Butted spokes – Double butted, but with different thickness butts on each end.

True, truing – A “true” wheel is one in which the rim is perfectly concentric and runs along a plane perpendicular to the axle.

A wheel which is “out of true” vertically will be out of round, and will give a bumpy ride even on a smooth road.

A wheel which is “out of true” horizontally may rub on the brake shoes at part of its revolution, causing excessive drag…or causing the brake to be adjusted looser than it should be to prevent this drag.

Tube – Inside of all modern bicycle tires you will find an inner tube, which is basically a rubber balloon with a valve that fits through the rim so that you can inflate it.

Tubular – A type of tire mainly used for racing. A tubular tire has no beads; instead, the two edges of the carcass are sewn together (hence the term “sew-up”) with the inner tube inside. Tubulars fit only on special rims, where they are held on by cement.

Twenty Niner – or 29er. The so-called “29 inch” tire size is not actually a new size, it is just a new marketing term for 622 mm (700C) wheels with fat tires.

This size is probably a good option for taller riders for off-road use, compared with 559 mm (26 inch decimal) wheels. Larger diameter wheels don’t sink as far into holes so they will give a better ride in rough conditions.

For shorter riders, wheels this large will cause unfortunate compromises in frame geometry, so they’re probably not a good option for riders of short or medium height.

U.S.T. - Universal System Tubeless. The most common system of tubeless tires/rims for bicycle use.

Valve – The part of the inner tube that permits air to be added. There are three types used on bicycles, Presta, Schraeder.

Wheel (front or rear) – A hub, rim, and spokes all together; may also include the tire and tube. (tires and tubes usually sold separately).

Wheelset (front and rear) – Both front and rear wheel when sold or discussed together (tires and tubes sold separately).