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
Eccentric
- The general term "eccentric" refers to two circles whose center is not at the same point. The primary bicycle usage refers to the special bottom brackets used on better tandems and some other cycles, which allows the bottom bracket to be moved slightly for purposes of fine-tuning chain length.
A tandem synch chain runs between two bottom brackets, and the front bottom bracket is usually mounted in an eccentric. This is a cylindrical part with a large hole running parallel to its axis. This hole is sized and threaded to accept a normal bottom bracket assembly.
The cylinder mounts into an oversized shell located where a normal bottom bracket would be. The outer shell may use pinch bolts or setscrews to secure the moveable eccentric cylinder in position. Some eccentrics use a wedge bolt system, similar to that of a handlebar stem, so secure the cylinder.
-
- An elastic polymer, a springy plastic used commonly as a spring or shock absorber, particularly in suspension forks and similar mechanisms.
An "elastomer fork" is a suspension fork which uses elastomers as the active suspension element.
Endrick rims
- A style of rim found on most English 3-speeds that are designed for cable-operated brakes. This is a plain steel rim, with the braking surfaces slightly angled inward toward the hub.
Ergo, Ergopower ®
- A combined brake/shift lever for drop handlebars, made by Campagnolo. Similar to S.T.I., Ergo uses an auxiliary lever inside the brake lever to select larger sprockets, and a thumb button on the inboard side of the lever to select smaller sprockets. This has the advantage, compared with S.T.I., of using a different motion for upshifting and downshifting, reducing the risk of accidentally shifting the wrong way.
-
- European Tire and Rim Technical Organization. This is the modern system for designating tire and rim sizes, but it has been adopted by the International Standards Organization, so the designation "E.T.R.T.O." is obsolete. This is explained in detail in my article on Tire Sizing
Exage
- See Shimano Models and Buzzwords
Expander
- See wedge
Extension
- he length of the part of the stem that runs forward from the shaft to the handlebar clamp. Stems are available with different length extensions to allow the bicycle to be adapted to fit the rider. See also my article on Frame Sizing.
Extension (or "reach") is commonly measured from the centerline of the shaft to the center of the handlebar. Unfortunately, common industry practice is to measure this along the direction of the part that points forward. Since different styles of stems have different shapes, two stems with the same extension measurement may not have the same actual distance between the centerline of the handlebars and the steering axis.
Occasionally the term "extension" is used as a synonym for a handlebar stem, particularly one with a long extension.
Extension levers
- In the early '70's, many people bought bicycles with drop handlebars, for reasons of fashion, even though drop bars did not suit their casual riding style. Dia Compe invented bolt-on extensions that allowed Weinmann-type brake levers to be operated from the tops and middle of the handlebars, making this type of bar bearable for casual cyclists, since they never had to use the drops. This was so popular that Weinmann traded licensing with Dia Compe, so that each could copy the other's products.
This system has several drawbacks:
- The extension lever partially applied the main brake lever, reducing the available lever travel.
- The attachment hardware precluded the use of the top of the brake lever hood as a comfortable riding position.
- They encouraged the practice of riding with the hands on the top, middle section of the bar, which is a position that doesn't give very secure control, especially on bumpy surfaces, because the hands are too close together.
- The hardware that held the extension levers to the main levers was prone to fall off.
Other manufacturers produced similar systems, some of which addressed some of these difficulties.
Extenison levers are also known as "safety levers", "death grips", "suicide levers" and "turkey wings."
-
- See "Puller."
-
-
- 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. Also sometimes called "ferrules".
- A braze-on or other threaded fitting for bolting an accessory to a frame. This term is mainly used to refer to the threaded tabs on fork ends, to which you may attach fenders or racks.
Fastback
- A style of seat cluster in which the seat stays butt up directly against the back of the seat tube, rather than the sides. Sometimes supposed to provide a "stiffer", "harsher" ride. I don't believe it, but it is a light and nice-looking style.
-
-
-
- A metal or plastic fitting that slips over the end of a run of cable housing to provide a solid base for the end of the housing.
- Rim eyelet
-
-
Fairing
- A lightweight shell that covers all or part of the rider/bicycle. Fairings are primarily intended for improving the ærodynamics of the vehicle, and they are generally prohibited from organized bicycle racing.
Some fairings are designed less for ærodynamics than for the sake of protecting the rider from cold and rain.
-
- A covering for the upper part of the wheel, to protect the bicycle and rider from spray when riding in wet conditions. The best fenders run close to the wheels, and cover a large arc. They are supported by wire stays that attach to the fork ends. Short fenders that attach without stays do not give enough protection to be worth while.
Fillet brazing
- A process in which frame tubes are brazed directly to one another, without the use of lugs. The "fillet" (pronounced "fill-it") is the strip of brass melted along the seam to connect the steel parts. The fillet is usually filed smooth, so that the tubes seem to flow smoothly into one another with no sharp transitions.
Fit-Kit ©
- A proprietary system for fitting a bicycle to a rider. The Fit-Kit has two principal parts:
- Bicycle fitting: Various dimensions of the cyclist's body are measured, then entered into a book of tables (or a computer program) which will then suggest a frame size, starting saddle height, top tube/stem length, and seat tube angle.
- Cleat fitting: Fitting pedal cleats to the cyclists shoes, using a special pair of floating pedals with indicators. (Known as the R.A.D.--Rotational Adjustment Device) The indicators on the R.A.D. show the natural angle of the cyclist's foot on the pedal. By adjusting the cleats so that the foot engages the pedal at it's natural angle, harmful stress to the knee may be minimized.
-
- In a conventional threaded bottom bracket, the left cup is adjustable, and its position is secured by a lock ring. The right cup is not adjustable, its position is fixed, usually by a shoulder which presses against the side of the bottom-bracket shell. The fixed cup is screwed all the way into the bottom bracket, until it runs out of threads.
The fixed cup usually has a left-hand thread to prevent it from coming unscrewed due to the action of pedaling.
Bicycles with French or Italian threading have right-hand threaded fixed cups; these fixed cups must be tightened very firmly to keep them in position.
-
- A rear hub in which the sprocket is rigidly connected to the hub, without a freewheel. The pedals of a fixed-gear bicycle revolve whenever the rear wheel turns; coasting is impossible. This type of gearing is usually associated with track racing.See my article on fixed-gears.
Fixing Bolt
- The bolt which holds a cotterless crank onto its axle.
Flange
- A raised circular rib around a part.
- The usual use for this term in bicycle usage is to refer to the part of a hub that the spokes attach to.
Most hubs in current production are "small-flange" or "low-flange" designs, where the flange is no taller than it needs to be to provide a suitable place for the spoke holes to be drilled.
"High-flange" or "large-flange" hubs have a larger flange, usually drilled out for lightness. They are transmit torsional forces with less stress to the spokes than small-flange hubs do, but this is not a problem in practice with modern equipment. High-flange hubs can make a wheel with slightly greater lateral strength than equivalent small-flange hubs, because the spokes create a wider bracing angle to the rim. This makes them popular with track sprinters, who create greater-than-normal side loads on their wheels.
- A less common bicycle use of "flange" is to describe a particular style of axle nut, commonly seen on cheaper bicycles. See track nut.
-
- A branch of freestyle cyling done at ground level. Usually involves spins, and standing on different parts of the bicyle, sometimes moving forward, sometimes backward, sometimes balancing at rest. In flatland tricks, sometimes the bicycle is caused to move by turning one of the wheels directly with the hand or foot.
Flint snatcher
- British: Tire saver
-
- A double sided hub, intended to take a sprocket or freewheel on each side. The gear of a one-speed bicycle could be changed by removing the wheel, and installing it backwards. Most flip-flop hubs are intended to accept a fixed sprocket on one or both sides.
There is a special BMX variant of flip-flop hub which is intended to take a single-speed freewheel on each side. This type has a standard thread on one side, and a smaller thread on the other side, which fits special undersized 15- and 14-tooth freewheels. (There is not room to fit a freewheel mechanism inside of a 15-tooth or smaller sprocket, with a normal sized hub.)
-
- A property of a clipless pedal system that allows the rider to rotate the foot within limits, as opposed to a fixed cleat which holds the shoe at a fixed angle in the yaw plane.
-
- Forging is a process of forming metal parts by the use of heat and pressure. Forging develops a grain structure in the metal, which makes it stronger in the direction that it has been stretched. Forging is done in special molds called "dies", and when the dies are properly designed to take advantage of the grain structure introduced by the forging process, the resulting parts are stronger in the important directions than those manufactured by CNC machining
-
-
-
- Usually refers to the front fork, the part of the frame set that holds the front wheel. The fork is attached to the main frame by the headset. The fork consists of the two blades that go down to hold the the axle, the fork crown, and the steerer.
The term "rear fork" is sometimes used to refer to the part of the frame that holds the rear wheel.
-
- A flat piece of solid metal, with a slot to receive a wheel axle. There is one at the bottom of each fork blade, and another pair at the junction of the seat stays and chain stays. Lower quality fork ends are stamped from sheet metal; better ones are forged.
-
-
-
- The skeleton of a bicycle. The most common type of frame is called the "diamond" frame, and consists of two (of three, depending on how you look at it) triangles.
- The front triangle consists of the seat tube, the top tube, and the down tube...well, it also includes the head tube, so is is not a perfect triangle, but the head tube is usually fairly short, so it is pretty close to being a triangle. The front triangle holds the saddle, the bottom bracket, and, via the headset, the front fork.
- The rear triangle (or triangles, if you count both sides separately) includes the seat tube, seat stays and chain stays.
The diamond frame has evolved over the course of more than a century, and every dimension has been tinkered with and fine tuned to the point that it is a nearly perfect design for the tubular materials commonly used.
This is not to say that it is the ultimate, however. For some applications the cross frame is still viable, and for moldable materials, monocoque designs may yet eclipse the diamond. It is also not at all clear that the diamond design lends itself to suspension applications.
-
- Usually, a "frame set" will consist of the frame and fork. In some cases, it may also include a headset and/or a seat post, or other parts peculiar to the frame involved.
-
- Frame size generally refers to a measurement of the seat tube. This is measured from the center of the bottom bracket to somewhere near the top of the seat tube. Unfortunately, manufacturers disagree about where to figure the top of the seat tube, so the same frame may have as many as 8 different size numbers attached to it, depending on the manufacturer!
- Frame size may be measured in inches or centimeters.
- Some manufacturers measure "center-to-center", i.e. to the intersection of the center of the top tube with the seat tube.
- Some measure to the intersection of the top of the top tube.
- Some measure to the top of the seat tube (which protrudes a variable amount above the top tube.)
- Some measure, on bikes with a sloping top tube, to where the seat tube would end up if the top tube didn't slope!
- A further complication is that different bicycles have different-height bottom brackets, so the stand-over height of two different frames may differ, even though both are 58cm center-to-center!
If you ask a bike sales person "what size frame do I need", and get back a number as an answer, without specifying a particular make and model group, you are not getting good advice.
In my opinion, seat-tube length is not the most important frame dimension anyway. See my article on Frame Sizing for the details.
France
- Paradise on Earth for the cyclist. I have several pages on Cycling in France.
-
-
-
- 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.
-
- Stunt riding, and the bicycles evolved for this purpose from BMX-style bikes. Freestyle bicycles resemble BMX machines, but are heavier, more rugged, and feature pegs, platforms and other places to stand. Freestyle riding is divided into "flatland" and "aerial" classes.
Freestyle bicycles usually are equipped with the "Potts modification" and a "rotor" which allow the handlebars and fork to be turned 'round and 'round at will without tangling the brake cables.
-
- The mechanism that makes coasting possible. A ratchet mechanism that allows the rearsprocket(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.
Freewheels are normally sold with the sprockets attached, so this term is frequently used as a synonym for a cluster.
A standard freewheel attaches to a hub by screwing on to external threads that are part of the hub. The action of pedaling tightens the freewheel down on the threads, so no tools are required to install a freewheel.
To remove a freewheel requires a special tool, commonly called a "freewheel puller" or "freewheel extractor"
This tool is a splined unit that may be mounted in a vise or turned with a wrench. The splines engage matching splines in the interior (non-rotating) part of the freewheel body. Different brands of freewheels have used different spline patterns, but there is a recent tendency to standard on the Shimano pattern.
Older freewheels had simple notches and matching extractors with two or four prongs. This obsolete system was prone to failure, and it is easy to ruin the tool and the freewheel while trying to remove the freewheel. When using a prong-type freewheel puller, the tool should be secured against the freewheel by tightening down the axle nut or quick release skewer.
The standard I.S.O. thread for freewheels is 1.375 x 24 TPI
-
- Older French bicycles were made to different standards than most modern bicycles. Areas of difference include:
The letter "D" means "right" (Droite); "G" means "left" (Gauche).
Newer French bicycles are built to Italian or I.S.O. standards
For more details on this topic, see my article on French Bicycles.
-
- Shifting operated by a lever that moves smoothly through its range. With friction shifting, the rider must learn exactly how far to move the lever to get from one gear to another. If the rider moves the lever too far, or not far enough, the chain will not line up properly with the sprocket, causing noise and roughness. See index shifting
Front drive
- A front-drive tandem runs the primary chain from the front bottom bracket all the way to the rear wheel. The more common rear-drive setup runs from the rear bottom bracket.
Front drive is slightly heavier, due to the greater length of chain, and in some cases the stoker's right crank may interfere with the chain.
Front drive greatly reduces torsional stress on the frame: with rear drive, the stoker's bottom bracket is being pulled forward on the left by the synch chain, while being pulled to the rear by the primary chain. With front drive, the crossover takes place at the front bottom bracket, where both chains pull to the rear.
Front drive also makes chainline an academic, not a practical concern. Since the chain run is so long, all gear combinations may be used without running the chain at a sharp angle.
-
-
Gage
- See: Gauge.
-
- One of the three comprehensive systems for numbering the gear values for bicycle gears. It is the only system that takes crank length into account, giving a true value for the relative leverage of different gears on bicycles with different size wheels and cranks. Gain ratio has the further advantage of not needing any units. It is a pure ratio, and is the same whether you use metric or inch-based units to calculate it. See also gear inch and development.
For more detail on gain ratios, see my article on the subject.
Gas Pipe
- A derisive term for the "high tensile" tubing used to build cheap bicycles. Since low-end bicycles are made of low-quality steel, the builders compensate by using heavy, thick-walled tubes.
Gauge
- A measurement of thickness, particularly of wire. The major use of gauges in bicycle technlogy is for spokes. There are several different national systems of gauge sizes, and this has been a great cause of confusion. A particular problem is that French gauge numbers are higher for thinner wires, while the U.S./British gauge numbers are smaller for thinner wires. The crossover point is right in the popular range of sizes used for bicycle spokes:
U.S./British 14 gauge is the same as French 13 gauge
U.S./British 13 gauge is the same as French 15 gauge
Newer I.S.O. practice is to ignore gauge numbers, and refer to spokes by their diameter in millimeters:
U.S./British 13 gauge is 2.3 mm
U.S./British 14 gauge is 2.0 mm
U.S./British 15 gauge is 1.8 mm
-
- The "gear" of a bicycle relates to the mechanical advantage of the whole drive system. In a low gear, the pedals are easy to turn, but you have to spin very fast to get any speed up. In a high gear, the pedals are hard to turn, but you don't have to make them turn very fast to make the bicycle go fast.
The gear of a bicycle depends on the ratio between the sizes of the front and rear sprockets, and the size of the drive wheel. If the bicycle is equipped with planetary gears, they also affect the gear. There are several ways of designating gears numerically. See gain ratios, gear inches, and development.
For information on using your bicycle's gears, see my article: Everything You Wanted to Know About Shifting Your Bicycle's Gears, But Were Afraid to Ask
-
- One of the three comprehensive systems for numbering the gear values for bicycle gears. It is the equivalent diameter of the drive wheel on a high-wheel bicycle. It is calculated by dividing the chainwheel size by the rear sprocket size, then multiplying the result by the diameter of the drive wheel. See also gain ratios and development.
Gear case
- A chainguard that totally encloses the chain, usually found only on roadsters. Gear cases (also known as "chain cases") are extremely practical for utility bicycles. They keep the chain clean in all weather, and permit cycling in ordinary street clothes without risk of soiling. Unfortunately, a satisfactory chain case to work with derailer gears has not been developed, so they are only found on one-speed bikes or those with internal gear hubs. Sometimes inaccurately referred to as an "oil bath".
Goose neck
- Handlebar stem, particularly a stem with a long forward extension.
-
- Slang term for the smallest chainwheel on a triple crank set.
-
- A group is a set of parts for one bicycle from (usually) a single manufacturer. The practice of selling parts as a group (or "gruppo" in Italian) probably originated with Campagnolo in the 1960's.
A group would normally include (as a minimum) the following:
- Hubs
- Bottom bracket
- Derailers
- Shifters
- Brakes
If a particular manufacturer doesn't make one or more of these items, they may have some made under their name by another manufacturer to fill in their group. For instance, when Mavic was offering groups, they had everything above except for brakes, so they had brakes made under their name by Modolo and Dia Compe, and pedals by Look.
If the manufacture offers them, a group could also include:
Note the distinciton between a "group" and a "kit": In addition to the group, a kit includes everything needed to turn a frame into a bicycle: rims, spokes, tires, rim tape tubes, handlebars, saddle, etc.
The use of the Italian term "gruppo" is sometimes considered an elitist affectation, especially when referring to parts which are not of Italian manufacture.
-
