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Sheldon Brown's Bicycle Glossary E-F

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E-type Front Derailer

E-Type Front Derailer

A front derailer designed to be secured to the bicycle by the right side bottom bracket mounting ring, instead of clamping to the seat tube .

E-type derailers are commonly used on bicycles that have non-round seat tubes that are incompatible with standard clamp-type front derailers. E-type derailers do not provide any adjustment other than the high and low limit stops .

The benefit of this is that it is impossible to install one wrong. The downside is that they must be used only with the specific sizes of chainrings for which they were designed.

See also my Article on Front Derailers


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. For more details on this, see my article on Adjusting Tandem Synch Chains.

Eccentric bottom brackets are sometimes used on single bikes too, especially because they permit adjustment of chain tension without moving the rear axle. This is useful if the bicycle is fitted with a rear disc brake or an internal-geared hub.

White Industries makes a rear hub with an eccentric axle, designed to permit use as a fixed-gear or singlespeed without a chain tensioner, on frames with vertical dropouts .

Elan 12-speed hub

SRAM/Sachs briefly offered a 12-speed internal-gear hub. Unfortunately, it was a flawed design, and almost all of them broke. No parts are available, they can not be repaired.


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. Elastomers are also used in some suspension stems, seatposts and saddles.

En danseuse

From the French, "dancing on the pedals." Pumping; pedaling while standing up. This is not an efficient pedaling style, but sometimes gives a welcome relief by providing a change of position.

Cyclists who pedal this way a lot of the time often do so because their saddles are too low, or their gears are too high.

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.

English Racer

This is a term used by ignorant people in some parts of the U.S. to refer to a 3-speed "sports" type bike. This is a very foolish designation, because the bikes involved, while usually English, have absolutely no connection with racing.


Effective Rim Diameter. This is the rim diameter measured at the nipple seats in the spoke holes. The E.R.D. is needed for calculating the correct spoke length.

See also the Spocalc Spoke Length Calculator on this site.

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.

Erickson Gizzmo ®

Early models of Shimano 's STI brifters were only designed for use with double chainwheels. The Erickson Gizzmo was an aftermarket cam device that permitted a double type front STI shifter to work with a triple crank. The normal position had the lever facing down, and the STI brifter worked as a normal double, using the middle and large chainring. When you flipped the lever up, the cam moved and gave extra slack to the cable, permitting access to the granny gear .

Erickson Gizzmo


European Tire and Rim Technical Organization. This is the modern system for designating tire and rim sizes, but it has been adopted by the ISO, so the designation "E.T.R.T.O." is obsolescent.

This system is explained in detail in my article on Tire Sizing

Euro Bottom Bracket

BMX slang for an ISO /British bottom bracket , as opposed to a threadless "Ashtabula " American style bottom bracket designed for one-piece cranks .


See Shimano Models and Buzzwords


See wedge


The 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. Given the frame and stem designs commonly available at the time, it was generally impossible to get drop handlebars high enough up to allow a low-intensity rider to reach the drops comfortably.

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.

(Stem shifters were also popularized around the same time, and for the same reason.)

This system has several drawbacks:

Other manufacturers produced similar systems, some of which addressed some of these difficulties.

Extenison levers are sometimes known as "safety levers." Since many people believe they actually reduce safety, the slang terms "death grips", "suicide levers" and "turkey wings" are occasionally substituted.

In the early 21st century, an greatly improved system of "interrupter brake levers " appeared, with all of the advantages and none of the drawbacks of the older extension levers. These also have the advantage of being compatible with modern "æro" brake levers which work a lot better than the older style levers that had the cables coming out of the tops.


See "Puller."


Extrusion is a process for manufacturing aluminum parts of basically linear shape by squeezing semi-molten metal through a nozzle shaped to form the desired cross section. The process is very much like the way frosting cake decoration is done.

The principal application in bicycles is the fabrication of aluminum rims.


  1. 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".

  2. 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.


The process of finishing the flat surfaces of the frame and fork to which bearing assemblies attach. Correct facing of the head tube, fork crown, and bottom bracket shell ensures correct alignment of the headset and bottom bracket bearings. This is necessary to ensure good bearing performance and reliability.

Facing requires highly specialized milling equipment, among the most expensive of bicycle tools. Even minimal tools to do this job cost several hundred dollars.

False flat

A section of road that looks level, but is actually slightly uphill.

Raleigh Professional Fastback Seat Cluster 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 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.


Fatigue (metal fatigue) is the property that causes metal to break after repeatedly being bent past its yield point. This is a common cause of spoke breakage, and can also affect frames, handlebars and other parts.

A familiar example of metal fatigue is experienced if you open a pop-top beverage can then flex the top back and forth a few times.

Aluminum is more prone to metal fatigue than steel is, so aluminum parts have to be designed a bit stronger to make up for this characteristic.

Note, this is a very simplistic description of a rather complicated process.


Abbreviation for the babytalk expression: "Fall Down, Go 'Boom'"


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.

In Britain and the Commonwealth countries fenders are called "mudguards."


  1. 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.

  2. Rim eyelet

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.

See also Mike Rother's article on Fillet Brazed Schwinns on this site.

Fish mouth

See: Miter

Fit-Kit ©

A proprietary system for fitting a bicycle to a rider. The Fit-Kit has two principal parts:

  1. 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.

  2. 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.

Fixed Cup

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.

Fixed Gear

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

See the entry on "Track Hubs" for details.

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.


A raised circular rib around a part.


A branch of freestyle cyling done at ground level. Usually involves spins, and standing on different parts of the bicycle, 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.

Flexstem ®

A handlebar stem with a pivot and an elastomer bumper to provide suspension for the handlebar.

Flint Snatcher

British: Tire saver

Flip-flop hub

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 axis.

Pedals with float allow you to rotate your heel inward or outward to some extent before disengaging the cleat.

Folding Bicycles



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

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


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.

Joshua Putnam has a good discussion of forks and Bicycle Steering Geometry on his Web site.

Fork end

A flat piece of solid metal, with a notch or 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.

Rear fork ends originally had the opening facing backwards, but in the 1930s, the "drop out" type fork end was introduced. With drop outs, the slot opens at the lower front, or, in the case of vertical drop outs, straight down. The advantage of this is that it makes for much easier wheel changes, since the chain does not need to be derailed before the wheel can "drop out" of the frame.

The old-fashioned rear-opening style fork ends are still seen on some single-speed bikes, mainly as a retro fashion statement. The revival of rear opening fork ends is an unfortunate fad, making the bikes that feature this design less versatile and less convenient than they would be if they used drop outs.

4th hand

A plier-like tool that has one jaw with a mechanism to grab a brake or gear cable, and another which acts as a temporary housing stop. This tool is primarily used to pull brake cables tight while the anchor bolt is being secured.


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 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.

Frame Set

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

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!

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.


Paradise on Earth for the cyclist. I have several pages on Cycling in France.


A special type of rear hub used for freestyle tricks. Unlike most hubs, a freecoaster permits the bicycle to be rolled backwards without causing the cranks to turn backward as well.

The only other type of hub that offers this feature is a coaster brake. Freecoaster hubs use a similar mechanism, only without the actual brake.

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.

See also my article on Shimano Cassettes.


This is mainly a marketing term. Generally refers to off-road riding that is also off-trail. Freeride bikes are similar to downhill bikes, with long travel suspension, but are generally a bit lighter and are set up for climbing as well as descending.


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 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.

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 "bosses" (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 boss-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, the same as for standard I.S.O bottom brackets.

Freewheel Threading

TypeThread SpecificationEquivalent


1.375" x 24 tpi

1.370" x 24 tpi

34.92 x 1.048 mm

34.80 x 1.058 mm

French34.7 x 1 mm1.366" x 25.4 tpi
Italian35 mm x 24 tpi1.378" x 1.058 mm
Metric BMX30 mm x 1 mm1.181" x 25.4 tpi
See also the article on Freewheels on this site.
Freewheel vs Cassette Singlespeed Freewheel

One-speed freewheel


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.

Friction shifting

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

If your bike has friction shifters, consider upgrading to a modern indexed system. This is a major, very worthwhile upgrade.

Front Center

The distance from the bottom bracket to the front axle.

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.

Front-Freewheel System (FFS ®)

Shimano's Front Freewheel System. The freewheel was built into the bottom bracket, so that the chain would turn even when the rider was coasting. This was to allow shifting while coasting--a solution in search of a problem.

See the 1982 Shimano Catalogue on this site.

FSA ® (Full Speed Ahead)

Full Speed Ahead is a supplier of bicycle parts.

FSA ®, FSC ® (Phil Wood)

Field Serviceable Axle, Field Serviceable Cassette. Older Phil Wood hubs were pressed together with indusrial presses, and required special tools for service/bearing replacement.

In 1992, the axles were designed to be "field serviceable." FSA and FSC hubs can be dissassmbled with just two Allen wrenches , 5 mm for most models, 8 mm for the track hubs. You stick an Allen wrench into the cap at each end of the axle, and unscrew one from the other to release the axle assembly.

FSA Full Speed Ahead ® is also the brand name for a line of bicycle parts.


A cable housing stop. This is mostly Sturmey-Archer terminology.

Funny bike

An extreme time-trial bicycle, usually featuring a top tube that slants down toward the front. Funny bikes are built for all-out speed, with no regard for the rider's comfort.****

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