As time went on, the Bicycle Glossary has grown, and many of the pages became inconveniently large.
I have split the larger pages into smaller ones, but I realize that there may be external links pointing to the older pages. For this reason, I have maintained copies of the older pages at the same location.
This is one of the older pages, and the newer pages that were derived from it are liable to be more complete and up to date, so please follow the links below to the current version. Sorry for any inconvenience.
If one of my own pages had a link that took you to this page, it would be helpful if you would send me an email with the URL of the page that had the bad link, so I can update it.
Sheldon Brown
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- Chiefly British variant of B.C.D.. Stands for "Pitch Circle Diameter" but B.C.D. ("Bolt Circle Diameter") is preferable, because the term "pitch circle" has a different meaning when speaking of sprockets.
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- A group of cyclists riding close behind one another in a line, so that each cyclist can draft the cyclist in front, except, of course for the leader, who is taking a turn to pull the rest of the grop. The riders take turns pulling and drafting. A group of cyclists in a pace line can maintain a substantially higher speed than even the fastest of the group could do alone. See also: Audax and peloton
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- A special braze on with a slot to hold the end of the reaction arm of a hub brake to the chain stay without the need for a clamp or bolt. This makes removing and replacing the rear wheel of a bike with a hub brake considerably easier.
I believe this was first used on Santana tandems.
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- A bag that hangs alongside one of the wheels of a bicycle. They usually come in pairs. Well-equipped touring cyclists often use two pairs, on on the rear, the other on the front, for better weight distribution. If they are mounted so that the top of the pannier is below the top of the wheel, they are "low riders."
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- A pantograph is a 4-bar/4-pivot mechanical linkage that is used to copy designs, sometimes in different sizes. 2 of the corners are fixed, the tracing point is on one of the movable corners and the engraver is on the other. If the 4 arms are all the same length, the copy is the same size as the stencil, but by varying the arm length you can make a pantograph enlarge or reduce graphics.
A pantograph with an engraving tool is commonly used to engrave names in bicycle parts. High-end bikes, particularly Italian ones, sometimes have the frame builder's name "pantographed" on the handlebar stem, cranks/chainrings, lugs, etc.
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- A parallelogram is a four sided geometric form, in which opposite sides are of equal length. A rectangle is a paralellogram in which the angles are 90 degrees.
A parallelogram linkage with pivots at the four corners will allow the angles to change as it flexes, but the facing sides always remain parallel to one another. This is a very useful mechanism for derailers, because it allows the derailer cage to move sideways while remaining parallel to the chain, and without the friction that would result from a sliding motion, as used on older plunger-type**** derailers.
This type of linkage is also used in some V brakes to provide a more nearly horizontal motion to the brake shoe, and to keep the shoe angle constant.
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- 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: http://www.parktool.com/catalog.htm
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- 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.
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- A single-ended socket wrench with a flat handle, particularly the Campagnolo 15 mm wrench made for tightening crank fixing bolts and track nuts.
The name derives from the fact that racers on a tight budget would often have to make due with peanut-butter sandwiches while on the road, and in the abscense of kitchen facilities, they would use the handle of this wrench to spread the peanut butter on their bread.
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- The part you put your foot on. The axles of the pedals screw into the cranks.
Pedal Threading
Direction
The right pedal has a normal thread, but the left pedal has a left (reverse) thread.
The reason for this is not obvious: The force from bearing friction would, in fact, tend to unscrew pedals threaded in this manner. The fact is, however, that it is not the bearing friction that makes pedals unscrew themselves, but a phenomenon called "precession".
You can demonstrate this to yourself by performing a simple experiment. Hold a pencil loosely in one fist, and move the end of it in a circle. You will see that the pencil, as it rubs against the inside of your fist, rotates in the opposite direction.
Ignorant people outside the bike industry sometimes make the astonishing discovery that the way it has been done for 100 years is "wrong." "Look at these fools, they go to the trouble of using a left thread on one pedal, then the bozos go and put the left thread on the wrong side! Shows that bicycle designers have no idea what they are doing..."
Another popular theory of armchair engineers is that the threads are done this way so that, if the pedal bearing locks up, the pedal will unscrew itself instead of breaking the rider's ankle.
The left threaded left pedal was not the result of armchair theorizing, it was a solution to a real problem: people's left pedals kept unscrewing! I have read that this was invented by the Wright brothers, but I am not sure of this.
Thread Sizes
- Most pedals have 9/16" x 20 tpi threads.
- Pedals for one-piece cranks are 1/2" x 20 tpi.
- Older French bicycles used a 14 mm x 1.25 mm thread, but these are quite rare.
- In the early 1980s, Shimano attempted to popularize a very large thread size, which they called "Dyna Drive." This system was designed to place the pedal bearing inside of the crank, so that the foot could be slightly below the pivot point of the pedal bearing. This was believed to offer biomechanical advantages, but the system was not a commercial success, and has been abandoned.
Pedal Types
- Plain pedals rely on the rider's coordination to keep the foot properly located on the pedal. This type of pedal is most popular with beginner or unsophisticated riders, who fear being unable to put a foot down in a hurry.
- Toe-clippable pedals (sometimes known as "rat trap" or "quill" pedals) which work with stirrup-like clips and adjustable straps to hold the foot in place. These were the near-universal choice of knowledgeable cyclists until the 1980's. Toe-clip pedals, especially "platform" pedals, may be used either with normal street shoes or with special cleated shoes. The use of cleated shoes with toe clips, however, was made obsolete by the development of:
- Clipless pedals, which provide a positive connection between the shoe and the pedal, without the constriction of straps.
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- A densely packed group of riders, sheltering in each others' draft. In a mass-start race, most of the competitors usually end up in one large peloton for most of the race. The word is French, from a term that means rolled up in a ball...a related word, peloter, means to caress sensually, cuddle.
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- A high-wheel bicycle. This term comes from old English coinage, where the penny was a very large coin, the farthing a very small one.
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- The synchronization of a tandem's cranks. Most tandems are set up so that the cranks are "in phase", that is to say, that the pilot's and stoker's pedals go up and down together at exactly the same time.
Tandemists sometimes like to experiment with different phasing of the cranks. One alternative is "90 degrees out of phase", where one set of cranks is horizontal while the other is vertical. This produces a smoother power flow, although it is a debatable whether this matters. Out of phase cranks complicate high-speed cornering, since both riders cannot have their cranks horizontal at the same time.
Out-of-phase cranks disrupt the unity of a tandem team, since the two riders are not moving in the same direction at the same time. As Osman Isvan says:
"There are essentially three entities riding a tandem:
The captain, the stoker, and the spirit.
It is the spirit who likes in-phase cranks."
Some tandemists prefer a setup that is only slightly out-of-phase, typically with the pilot's chainwheel one or two teeth ahead of the stoker's.
Pie plate
- Slang for a spoke protector or a chainwheel guard.
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- A California-based maker of very high quality bicycle parts. Phil Wood is best known for hubs, which were the first modern cartridge-bearing hubs, using large diameter axles that never bend or break. Many cyclists consider them the finest available. Phil Wood also makes cartridge-bearing bottom brackets assemblies. These are used with separate rings that are available in a wider variety of threadings than those of any other manufacturer. For some obsolete bottom bracket threading systems, Phil Wood is the only current product that will fit.
The company also supplies an excellent grease and oil.
The Phil Wood spoke machine is an all mechanical machine that cuts and threads spokes to any desired length in a single operation, by simply pulling a lever. This machine is in a class by itself.
Formerly, Phil Wood also made pedals and one of the first disc brakes ever designed for bicycles. These products were less successful than those mentioned above. The disc brake, in particular, is considered quite dangerous by some. They were prone to fracture of the disc, which would cause abrupt, total brake failure, with no warning.
Pilot
- The front rider of a tandem, also called "captain" or "steersman".
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- When a round part is held inside another round part, but adjustability is desired, the outer part will often have a slot or gap. This gap will be bridged by a bolt that can squeeze or "pinch" the outer part so that it will clamp onto the inner part. Such a bolt is called a pinch bolt. Most bicycles use pinch bolts to secure the seatpost into the seat tube of the frame, and to secure the handlebars to the stem. Threadless stems usually use pinch bolts to secure the stem to the steerer. Many tandems use pinch bolts to secure their eccentric bottom brackets.
The bolt may fit through "ears" that are attached to the outside of the outer part, or it may close the gap of a split collar which surrounds the upper part of the seat tube.
A few older bicycles used a collar and pinch bolt to secure a handlebar stem inside of the steerer. This system is particularly common on folding bicycles to allow the use of a quick-release for the handlebar stem. This required a compression slot to be cut into the steerer, which could constitute a stress riser.
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- A hole in an inner tube caused by getting the tube pinched between the rim and a hard, sharp object, such as a rock, curbstone or the edge of a pothole.
Pinch flats (also known as "snakebites" because there are usually two small holes in the tube, as if made by the fangs of a snake) are usually caused by carelessness or riding under-inflated tires. They can also be caused by the use of a tire which is too narrow for the weight it is asked to carry.
If the tire is too soft, or too narrow, it is easy for it to bottom out when striking an obstruction.
If the tire is hard enough and plump enough to carry the weight, the air will keep the tube from being pinched between the rim and the road hazard.
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- Italian for "Track" as opposed to "strada" (road.)
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- The pitch of a chain is the distance between adjacent drive rollers. All modern bicycles use 1/2" pitch. Some older chains, especially those used on track bicycles used 1" pitch chain (see skip link and block chain.) For a while, Shimano experimented with a 10 mm pitch for track use, but it never caught on.
Sometimes people mistakenly refer to "track pitch" vs. "road pitch" when they are really referring to the wider (1/8") sprockets used on single-speed bicycles, instead of the 3/32" thick sprockets used on derailer-equipped bicycles.
The pitch of a nut or bolt is the distance between threads. S.A.E. fasteners have the pitch specified in terms of how many threads there are per inch (T.P.I.). Metric threads are specified by the distance between threads, in millimeters.
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- The effective diameter of a sprocket. This is measured from the centers of the chain rollers, rather than from any physical part of the sprocket.
Some British writers, confusingly use the term "Pitch Circle Diameter" as a synonym for "Bolt Circle Diameter."
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- Damage to a metal surface that takes the form of one or a series of small craters or pits in the surface. This is a type of failure often seen in worn-out bearing cones.
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- A planetary gear train consists of a stationary "sun" gear, surrounded by several (usually 3 or 4) identical "planet" gears which mesh with it. The planet gears, in turn, mesh with a hollow "gear ring" which has teeth on the inner surface. The gear ring rotates faster than the planet gears.
If the drive sprocket is connected to the gear ring, and the cage that holds the planet gears is used to turn the wheel, the wheel will turn slower than the sprocket, thus providing a lower gear, compared with a simple hub driven by the same size sprockets.
If the drive sprocket is connected to the planet cage, and the gear ring drives the wheel, the result is a higher gear.
Most three-speed internally-geared hubs use these two configurations, along with the direct drive to provide the three speeds.
Internally-geared hubs with more than three speeds use multiple sun pinions and sometimes multiple planet gears in the same manner.
See also my articles on English 3-speeds and Sachs/Shimano 7-speed hubs.
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- Chainwheel. This usage is French, not English, and it is pretentious to use it when writing or speaking English.
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- A pedal intended for use with toe clips and soft-soled shoes. Platform pedals are usually single sided, and intended exclusively for use with toe clips. One side has a large flat surface to support the rider's foot, spreading the pressure over a wide area for comfort. The other side usually has only the structural support ridges that hold the platform, and is not intended to be used for pedaling. The best known platform pedal was the French Lyotard "Marcel Berthet" model 23, one of the most elegantly designed bicycle parts ever.
Platform pedals have superior ground clearance to double-sided pedals, and provide easier, faster entry to the toe clip than other styles.
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- A scissor-like gripping tool that multiplies the strength of a user's hand. Designed for grabbing irregular shaped objects.
Pliers have very limited use for bicycle work, and many bicycle parts are damaged by incompetents who try to use pliers for a job that really calls for a wrench. This commonly results in damage to the surfaces of the nuts or bolts so abused, as the serrated jaws slip around.
Many accidents are caused by people attempting to secure axle nuts with pliers. This cannot be done by people of normal hand strength, the nuts will not be tight, and the wheel is liable to fall out. Never use pliers to tighten nuts or bolts!
Locking pliers, such as Vise-Grips ® can grip a nut or bolt hard enough, but will ruin the driving surface so that it will be unusable with the correct tool.
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- A tire inflated with air, as opposed to an airless tire.
In general usage, "pneumatic" refers to any device which operates by air pressure.
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- Although there have been bicycles specifically designed for bicycle polo, the term is most commonly used as a synonym for "wheelie bike"
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- see "Banana seat"
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- Shimano's original system of indexed shifting. Positron placed the detents in the derailer, which had no return spring. Some versions of Positron used a double cable to push and pull the derailer back and forth, other versions used a solid, push-pull cable.
Most other indexing systems place the detents in the control lever.
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- East coast term for "taco"
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- A system of running the front brake cable through the stem wedge bolt so that the cable will not hang up when the handlebars and fork are rotated. Used on freestyle bicycles. See also rotor.
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- An initial load on a part, which is independent of the load it is designed to bear.
- Bearings are commonly supplied with a slight pre-load, that is, they are made to be slightly tighter than would permit the freest possible motion. This is to prevent slop in the bearing, and to ensure that the stresses are shared by multiple balls or rollers.
- Some suspension parts, particularly suspension stems and seatposts are designed with an adjustable pre-load. This is adjusted so that in carrying the rider's steady-state weight, the part is pressed up against a stop, so that it doesn't bounce up and down with minor road irregularities or body movements. When a more serious bump is hit, the suspension will respond to the greater load thus applied.
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- The narrow valve used on most high-performance bicycles, and all tubulars. Also known as a "French valve". The wider Schræder (automotive style) valve is used on children's bicycles and utility bicycles.
Presta valves have built-in valve caps, which must be opened before you can pump them up. These caps are "captive" nuts, which cannot be removed. Since there is no spring in a Presta valve, this knurled nut must be retightened after inflating the tire, or the valve may leak slowly.
Presta valves are light, and don't require as large a hole in the rim. Since the don't use a spring, they can be easier to pump with a hand pump.
Separate valve caps are not needed with Presta valves. Valve caps, lock rings and Schræder adaptors can actually be dangerous, if you ride tubular tires.
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Presta valve
closed | Presta valve
open | Presta valve
with adaptor
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There is a third type of valve, very rarely seen, which has a bottom similar to a Schræder and necks down to about the size of a Presta. This is a Woods valve, formerly popular in the British Isles and Asia. These low-tech valves work with rubber tubing and spit. This is also sometimes referred to as a "Dunlop" valve.
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- A tandem has at least two chains. The primary chain is the final drive chain that runs to the rear wheel, usually from the rear bottom bracket. The primary chain is similar to the chain on a solo bicycle.
In addition to the primary chain, a tandem will have one or more "timing" or "synch" chains, connecting the bottom brackets
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- In pace line riding, the riders usually take turns riding in front, allowing the others to draft behind them. The rider in front is "taking a pull", pulling the others along in his or her slipstream.
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- A specialized tool for disassembling parts. In bicycle technology, there are two common types:
These tools are also more formally known as "extractors."
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- Bicycles use pulleys both for chains and for cables.
Chain pulleys
- Most rear derailers use two pulleys in a spring-loaded cage to regulate the tension of the chain as it runs over different sized sprockets. The upper pulley is called the "jockey" pulley, the lower one is the "tension" pulley.
- Idler pulleys are used to:
- ...lead a chain around an obstruction (as on most SWB recumbents, where the front wheel gets in the way of a straight chain run.)
- ...adjust the tension on a chain (as with tandem synch chains.)
- ...apply extra tension and guidance to prevent accidental derailment on downhill bicycles.
Cable pulleys
- Pulleys have traditionally been used on 3-speeds to lead the cable where it crosses the seat tube, either at the top (following the top tube/seat stay) or the bottom (following the down tube/chain stay) of the seat tube.
- Many early '90s mountain bikes used a pulley at the bottom of the seat tube, to permit top-pull cable routing with bottom-pull front derailers. Since top-pull front derailers became readily available, this system has been obsolete.
- Accessory cable pulleys, such as the Avid Rollamajig ® are sometimes used in place of the traditional loop of cable housing where the cable enters the rear derailer.
- Pulleys are also used on brake cables:
- ...for center-pull/cantilever rear brakes on ladys' bicycles, where the cable has to make a sharp bend after it runs up the back of the seat tube.
- ...in some mountain-bike handlebar stems, where the housing enters in line with the stem extension, and the bare cable runs around a roller toward the cantilever. (Some people believe that this is dangerous, due to potentially higher risk of breaking the cable due to repeated flexing of the cable.)
- Eccentric pulleys are sometimes used to change the mechanical advantage of a cable. This is most commonly done to permit the use of direct-pull cantilevers with conventional levers.
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- A type of track racing for two cyclists or two teams, who start 180 degrees apart on the track. The race ends when one rider or team passes the other, or, after a fixed number of laps, with the victory going to the rider or team who has gained on the other.
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- In Fit-Kit © terminology, this is a factor based on the relative length of the femur compared to the rest of the leg. A large Q-factor is interpreted as an indication that the rider in question needs a frame with a shallower seat tube angle.
- Also, another name for the tread of a crank set
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- Buttedto four different thicknesses, including the thin section.
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- A tandem for four riders.
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- 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.
When quick-release wheels started being supplied on bicycles intended for the general consumer market, ignorant users caused a rash of accidents due to front wheels falling off. The resulting lawsuits led to the addition of lawyer lips to most front forks, greatly reducing the convenience of quick release wheels.
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- To facilitate wheel changes, most high-performance road bicycles have a quick release mechanism that allows the brakes to be temporarily opened a bit wider than usual, so that the tire can fit through the brake pads.
Some brake quick releases are located in the brake levers, which is the best place for them. This type of quick release allows the brakes to work normally even if the user forgets to reset them after use.
Other quick-releases are located at the caliper or on the cable hanger. These must be manually reset after use, or the brakes may run out of travel. The better caliper-mounted QR's feature a cam which allows a variable setting. This is of use to racers who may knock a wheel out of true, because they can temporarily loosen the QR as much as it takes to get the bent wheel to clear the brake shoes.
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- In the early days of the mountain bike, West coast riders often liked to ride up their mountains with the saddle set at a normal height for efficient pedaling, then drop it down low for the descent. Going down the mountain, they didn't need to pedal, and the lower saddle made it easier to move their weight around for maximum control and shock absorbency.
This feature was carried over when mountain bikes made it into the mass market. Naive bicycle buyers think that a quick-release seatpost is a nifty feature, but it is actually much more trouble than it is worth for most cyclists. In particular, it is very undesirable for urban cyclists, because it has made it necessary to worry about having your saddle and seatpost stolen, a crime that was virtually unknown before the advent of quick-release seatposts.
In the mid 1980's there were also seatposts with quick-release saddle clamps, which allowed the saddle to be moved back and forth over a considerable range. This turned out to be a solution in search of a problem, and was not embraced by the marketplace. Part of the reason for this may be the fact that these seatposts were marketed for mountain-bike use, but were much too short for normally fitted mountain bikes.
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- The vertical part of a comventional handlebar stem.
- A traditional-style pedal for use with toe clips and straps is sometimes called a "quill" pedal, but I have been unable to discover why.
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