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Sheldon Brown's Bicycle Glossary Cn-Cz

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Computerized Numerical Control. This refers to modern milling machines and other machine tools that can carve complex parts from solid billets. Although CNC parts are not as strong as forged parts, they can be made into more complicated shapes than is possible with forging or conventional casting.

See also Jeff del Papa's article on Forging, Casting & CNC Machining on this site.

Most bike parts in current production have some level of CNC finishing. When advertising makes a big deal about it, this is usually an indication that the part concerned is "machined from billet", i.e. that it is entirely sculpted from a big lump of metal. This is actually very much inferior to processes that begin with forging and just use the CNC for the final finishing, because the billet (big lump of metal) will not have the desirable grain structure of a forged part.

Coaster Brake

A type of rear hub which incorporates a brake which is operated by pedaling backward. It is called a "coaster brake" because it combines the functions of the brake and freewheel ("coaster") in a single unit. When the coaster brake first appeared on the scene, freewheels were uncommon, if they were even in use at all, in the era of the spoon brake.

An unusual feature of coaster brakes is that this type of rear hub is that it permits the bicycle to be rolled backward without causing the cranks to turn backward as well. This is a useful feature in some freestyle tricks. There is also a type of hub called a "freecoaster" that permits this. It is basically a coaster brake hub with the brake mechanism removed.

See my Article on Coaster Brakes

Campagnolo Cobalto Brake Cobalto ® Brake (Campagnolo)

A luxury version of Campagnolo's traditional Record side-pull brake with a decorative blue jewel in the brake arm locknut.

These date from 1983, Campagnolo's 50th anniversary year.


Popular term for a rear sprocket. Sometimes incorrectly used as a synonym for cluster, which is actually a group of cogs.

Originally, "cog" referred to just a single tooth on a "cog wheel." Then "cog wheel" was shortened by popular usage to "cog."


Noted Italian maker of frame tubing.

Comfort Bicycle

The original runaway popularity of mountain bikes was mainly related to their greater comfort for casual cyclists, compared to the drop-handlebar, skinny-tire sport-touring bikes that had been the predominant adult style through the '70s and early '80s.

As mountain-bike racing became more organized, mountain bike designs started to morph into a more competition-oriented riding position, with longer top tubes , lower handlebars, narrower saddles, shorter wheelbases and more upright frame angles.

By the late '90s, this trend had gone so far that many casual/beginner cyclists were finding mountain bikes uncomfortable.

In response, the industry came up with what is commonly known as a "comfort bike." Typical comfort bikes resemble mountain bikes in wheel size, brake and gear equipment, but also differ in several ways:

  • Shorter top tubes, for a more upright riding position.
  • Taller, often adjustable, handlebar stems, also for a more upright riding position.
  • "Riser" handlebars, also for a more upright riding position.
  • Wider saddles with springs (and/or suspension seatposts.)
  • Smooth, wide tires for quiet and comfort on smooth surfaces.
  • Lower bottom brackets for easier mounting/dismounting .

In many respects, the comfort bike harkens back to the riding style/position of the classic English roadster, only with modern gears and brakes.

Comfort bikes are often seen as slower, stogier versions of "hybrid" bikes, and are targeted at pretty much the same market.

Cold Set

To bend a metal part (without heating it) so far that it exceeds its yield strength, and assumes a new shape.

This is a common procedure for aligning and repairing steel bicycle frames. This buzzword sounds more scientific than "bending."

It is a routine procedure for updating older frames to accommodate newer rear wheels that have wider spacing, when upgrading to modern gearing. This is not recommended for frames made of more brittle materials, such as aluminum, titanium or carbon fiber.

Command Shifter ®

A wing-nut-like shift lever developed by Sun Tour. It mounts on drop handlbars, just above the brake lever, and allows shifting from various parts of the handlebar.

Compact Crank

A double-chainring crankset with that permits the use of smaller chainrings than will fit with the common 130 mm B.C.D. Most "compact double" cranks use the old standard 110 mm B.C.D., which permits the use of chainrings as small as 33 teeth (more commonly, 34 or 36 teeth.)

Compact crank sets usually come with a 50 tooth chainring, and are normally used with an 11 or 12 tooth top sprocket in back.

110 mm B.C.D. double cranks with full-sized chainrings (52-42, 52-40, etc.) were common in the late'70s and early '80s, but they had become nearly extinct for double chainrings. The rebirth of this format, with smaller rings, was pioneered by Tyler Hamilton who used one of these in the 2003 Tour de France

Compact Drive (MTB triple)

A system of using smaller-than-normal sprockets front and rear. This has the advantage of saving a small amount of weight, improving chainwheel clearance for mountain bikes, and perhaps making a slight improvement in shifting. This is done by going to a smaller bolt circle, typically 94 mm/58 mm or 104 mm/64 mm B.C.D.

The downside of compact drive is significantly reduced chain life, and decreased interchangeability of parts. I consider compact drive to be a very bad idea for mountain bike use, but it seems to have become ubiquitous.

For mountain bike usage, compact drive typically uses 22/32/42 tooth chainwheels as opposed to the 48-38-28 or 46-36-24 used on earlier mountain bikes.

The original mountain bike cranks were mosly 5-bolt 110 mm/74 mm BCD. "Compact Drive" cranksets usually use the 94 mm/58 mm BCD 5 bolt, or 104 mm/64 mm 4 bolt cranks, as opposed to full-size systems that have 24-28 tooth lows and 46 or 48 tooth highs on 110 mm/74 mm BCD cranks.

Compact Frame

Traditional "road" frames have been built with level top tubes since the early 1900s. The influence of mountain and BMX bike design has led to the increasing popularity of frames with sloping top tubes, higher at the front.

"Compact" road frames have sloping top tubes, and are intended to be used with a long seatpost. Compact frames are a little bit lighter than traditional ones, but this is partially offset by the weight of the longer seatppost. Some riders believe these frames are stiffer.

When the down tube and seat tube intersect directly above the front axle, as is usual with a road frame, weight loading only tensions the down tube and compresses the top tube. When the intersection is farther back than the axle, the bending loads on these tubes require the front end of the frame to be of stronger construction.

Manufacturers like compact frames because they are more versatile in terms of fit. Usually 3 or 4 sizes are enough to fit 98% of customers. This saves a lot of money for a manufacturer who doesn't need to deal with so many different sizes.


Literally, a material made up of different materials joined together. In bicycle tecnhologies, the most common uses refer to the use of carbon or boron fiber, or fibreglass, bonded together with epoxy resin.

Compressionless Housing

Cable housing consisting of a bundle of more-or-less parallel wire strands, instead of the single coiled strand of normal housing. This is used for handlebar-mounted shifters, because the effective length of the housing doesn't change significantly as the handlebars are turned and the cable flexes. This is part of what makes reliable indexed shifting possible.

Compressionless housing must not be used with brake cables. It is not strong enough, and can rupture, causing brake failure. See also my article on Cables.


See cup-and-cone. Most bicycle ball bearings consist of a cup-shaped and a cone-shaped race, with the bearing balls rolling between them. The term "cone" usually refers to the cone-shaped nuts on a conventional hub axle. See my article on cone adjustment.

Cone Wrench

A special thin wrench required to adjust the bearing cones on a hub. Most front hubs use a 13 mm, most rears use 15 mm.

Contrôle, Control

A checkpoint on a randonnée

Cottered Cranks

An older way of attaching the cranks to the bottom-bracket axle, by the use of cotters, wedge-shaped pins threaded on one end to accept a nut. See my article on Cottered Cranks and my Tool Tips article on tools for Cotterless Cranks

Cotterless Cranks

The modern type of three-piece crankset. Although one-piece cranks don't use cotters either, the term "cotterless" normally refers to two-piece or three-piece sets.

The bottom bracket spindle (axle) used with a standard cotterless crank has tapered square ends, which fit into matching tapered square holes in the cranks. The ends of the axle are threaded, either male or female, and a bolt or nut (called the "fixing" bolt/nut) pulls the crank tightly onto the end of the axle.

The nut or bolt head is recessed into the crank, in a hole with threaded sides. These threads can hold a decorative cap that hides the fixing bolt/nut, but their main function it to provide a purchase for the "crank puller", a special tool that is needed to remove the crank from the axle.

See my Tool Tips article on Cotterless Cranks

See also the Bottom Bracket entry in this Glossary. *****


When a bicycle turns, it must lean into the direction of the turn so that the tilt of the bicycle and rider counterbalances the "centrifugal force" created by the act of turning.

In order to turn left, you start by turning the handlebars to the right for a moment. This moves the front wheel out to the right of the center of gravity, so the bike will start to fall to the left. This is immediately follwed by turning the handlebars to the left to cause the bike to remain in balance, which also creates the desired left turn. "Countersteering" refers to the momentary motion of the handlebars in the opposite direction of the desired turn. usually, this is accomplished through the normal slight weave of the bicycle to maintain balance.

Some people, particularly motorcyclists, make a big deal out of this as if countersteering is some special advanced riding technique that you must learn to become an expert bike handler. It isn't. It's just a fancy sounding name for the normal process by which any two-wheeler (or even a unicycle) is controlled.

Hovever, to be ready to swerve quickly out of danger, it is useful to practice quick, forced countersteering so as to initiate a furn as quickly as possible. The amount of countersteering needed decreases as speed increases, and practice will teach you how to approach the limit of traction without exceeding it and skidding out.

See also my article on Braking and Turning

Cow-Horn Handlebar

A handlebar which is straight or tilts down slightly either side of the stem, and is curved forward and upward at the ends. It is popular with time trialists and is commonly used along with forearm rests and clip-on æro bars.


Consumer Product Safety Commission, a U.S. Federal Government agency. This agency has a long history of incompetence in attempting to increase the safety of bicycles. It is also complicit in the Reflector Conspiracy.


The arm which connects the pedal to the bottom bracket axle. Sometimes called a "crank arm", but this is redundant and inelegant. Call it a crank, or call it an arm, but please don't call it a "crank arm"

For information on interchangeability, see: Bolt Circle Diameter.

This site has an extensive article on cranks.

Crank pullerCrank Puller, Crank Extractor

Tool for removing cotterless cranks. A crank puller consists of a "nut" part which screws into the dust-cap threads of the arm, and a "bolt" part that fits through the "nut" part and presses against the end of the bottom bracket spindle, so the "nut" part pulls the arm off. Some crank pullers have a handle attached to the back of the "bolt" part, others require the use of a separate wrench to turn the "bolt" part.

See also my "Tooltips" article on Cotterless Crank Removal.

Crank Set, Crankset

At a minimum, a "crankset" consists of the two cranks, the chainwheel(s), and the stack bolts that hold the chainwheels to the cranks. In some cases, it also ncludes the bottom bracket axle and bearing assembly.

Crescent ® Wrench

Although "Crescent" is a trademark, it is commonly used in the U.S. to refer to a conventional, angled-head adjustable wrench regardless of brand (as opposed to a monkey wrench). Adjustable wrenches are better than nothing, but better mechanics rarely use them. Adjustable wrenches present a higher risk of damaging nuts or bolt heads by slipping than do fixed-size wrenches.

See my Tool Tips article on Adjustable Wrenches.


A criterium race consists of many laps around a short course. The course may be a few city blocks. Criteriums are good for spectators, less popular with racers.

A criterium bicycle will often have a somewhat higher bottom bracket than a road-racing bicycle, to allow pedaling through the turns. (There are a lot of turns in a criterium!) Criterium bicycles are designed with a particular eye to manuverability, because the peloton in a criterium is likely to be large and dense. Criterium bicycles are not usually built for comfort.

Croce d'Aune ®

A late '80s Campagnolo gruppo (named for the mountain pass where Tullio C. got the idea for the quick-release hub) only made for a year or two. It does not index with current shifters, it went with the obsolete "Synchro" system, which hardly anybody could get to work.

"Crochet Type Rim"

This is not an English term. Some tires from the Dutch company Vredestein have a translation error in which they say their tires should be mounted on "crochet type rims only." What they mean is hook-edge rims.

"Crochet" is French for "hook." Evidently somebody at Vredestein got the two languages mixed up.

Cross Bicycle

The term "cross" bicycle is used to refer to two distinct types of bicycles, which have a few similarities, but many differences.
  1. Cyclocross or "cross" bicycles are built for cyclocross racing. They typically have drop handlebars with handlebar-end shifters. Because they must often be lifted up and carried while running, they are light and usually use tubular tires. Cyclocross tires are fairly plump, and have a knobby tread for better traction. Cantilever brakes are normally used to provide better mud clearance. Traditional cyclocross bicycles were based on road-racing frames that had outlived their usefulness, but modern cyclocross riders normally use purpose-built 'cross frames, or sometimes mountain bikes.

  2. Hybrid bicycles are also sometimes referred to as "cross" bicycles, because they are a cross between a mountain bike and a road bike.

Cross Country

  • Normal, pedal-powered off-road mountain-bike riding, as opposed to down hill racing.

  • Riding across the whole width of a country (generally referring to the U.S.)

Cross Frame

A cross frame is basically made up of two intersecting members, forming a cross. The vertical member is the seat tube, and, perpendicular to it is a backbone, which might extend and split to form rear stays. This type of frame is not as naturally strong geometrically as the more common diamond frame, so it gets its strength from the use of large diameter tubing, or monocoque construction, particularly for the backbone. There are often gussets or struts added to provide a measure of triangulation to the frame.

Crossover Drive

Most tandems use crossover drive, in which the primary chain runs on the right, just like that of a solo, but the sync or timing chain is on the left side of the bicycle. The drive from the sync chain "crosses over" to the primary chain at the stoker's bottom bracket (or if the tandem has front drive, at the front bottom bracket.)

See also John Allen's article on tandem drivetrains..

Crossover Gearing

This refers to a derailer gear system in which the jumps between chainwheel sizes are approximately the same as the jumps between adjacent rear sprockets. This type of gear setup provides a particularly simple shifting pattern, requiring no double shifting at all, but at the price of creating a large number of duplicate gears, and limiting either the overall range of gears or the closeness of spacing.

Crow's-Foot Spoking

A novelty spoking pattern involving both semi-tangent and radial spoking. The spokes are in groups of 3, and where two semi-tangent spokes cross a radial spokes the three spokes are tied and soldered together. See for more info on whimsical patterns like this.


The upper part of the front fork, where the blades and steerer attach together. See also unicrown.


"Cruiser" is the currently popular name for what used to be called a "balloon tire" bike. This style of bicycle was most popular in the 1940s and 1950s. Cruisers are usually characterized by 26 x 2.125 tires. (If they have 1.75 or 1 3/4 tires, they are considered "middleweights".)

The upper top tubes and stays are usually curved for a "streamlined" look. Older cruisers usually had a straight lower top tube; later models had cantilever frame designs. Cruisers are built for ride comfort, not efficiency. Classic cruisers were spectacularly heavy, had only one gear, and a coaster brake.

This type of bike is quite impractical for hilly country, due to the weight, the lack of gears, and the low saddle position of older models. For this reason, cruisers traditionally were most popular in very flat places, such as Florida and the southern California coast, and became associated with beach resorts.

As a reaction to the gonzo image of mountain-bike marketing, cruisers seem to be making a comeback in popularity, even in places far from the beach. The new generation of cruisers is much lighter, thanks to modern materials and manufacturers who care about reducing weight. They are also now available with multi-speed gearing. The "neo-cruiser" appeals to aging baby-boomers who have nostalgic memories of the balloon-tire bikes or their youth.

The classic balloon tire bike, before it was known as a "cruiser" was also quite important to the history of cycling because it was in many ways the precursor of the mountain bike.

Another usage for the word "cruiser" refers to an adult-sized BMX bike, typically with 507 mm (24 inch) wheels.See als my article on Singlespeeds.

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.

In a conventional threaded bottom bracket, the cones are part of the bottom bracket axle, and the cups thread into the bottom bracket shell of the frame. The left cup is adjustable, to permit the bearing to be fine tuned. It has a lock ring to secure the adjustment. The right cup is the "fixed cup", usually having a flange that bumps against the edge of the bottom bracket shell when it is screwed all the way in. In the case of hubs and pedals, the cups are part of the hub shell or pedal body, and the cones attach to the axle. One or both of the cones is adjustable, and usually has a locknut and a keyed washer to secure it.

Cyclebinding ®

A clipless pedal system, introduced in 1984, earliest of the modern shoe-pedal systems. Unlike other systems, the Cyclebinding system used a recessed shoe into which the pedal's mechanism fitted. Cyclebinding was also the first "walkable" clipless pedal system.

It was very well received by consumers, but delays in production of the special shoes required caused the company to fail. This left the market open to domination by Look, and later Shimano's SPD system and others.


An electronic speedometer/odometer for bicycles. See my articles on Cyclecomputer Calibration, Installation, and Repair.


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 bicycles.

Cyclocross Brake Levers

This is another name for interrupter brake levers. There's nothing about these brake levers that is really cyclocross-specific, but they were first popularized under that description.


A device for measuring how far a bicycle has traveled, an odometer. Older cyclometers were mechanical, usually mounting down near the front axle. They would commonly have a star-shaped wheel sticking out next to the spokes, and a special striker pin, bolted on to one of the spokes, would turn the star wheel one point each time the wheel's revolution brought the pin past the cyclometer. This type of cyclometer was in common use from the turn of the century until the 1970's.

Star-wheel cyclometers, such as the Lucas unit, suffered two serious problems. They made an annoying "tink-tink-tink" noise. At high speeds, the star wheel would sometimes turn too far when hit by the fast-moving striker, then, the next time around the striker would hit the tip of one of the star points, sometimes knocking the unit out of position.

The Huret Multito solved these problems by substituting a rubber belt drive in an otherwise similar unit.

With the development of inexpensive electronic cyclecomputers, mechanical cyclometers became obsolete.

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Revised April 12, 2010 by John Allen

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