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It would be helpful to have a common place to list terminology, I'll start it off

Some Rules

  • Make sure you only put one term per answer!
  • Try to include an image if applicable
  • Include sources that contain detailed information

Also, I made this a community wiki, so that anyone will be able to edit it, and to stop rep-hoarding


There's a handy reference at the Park Tool Co. website, a bike repair map; it's a diagram of a bike with all the parts labeled, and is very handy! At the moment, the diagram is up at parktool.com/blog/repair-help. (They've changed the URL in the past, so this link may break.)


Edit: This page is meant to identify what things or concepts are (as per this thread in meta). If you want to recommend an accessory or a specific product you've found handy, please use the accessories page.


Contents: (As of 03 Nov 2012)

Bearing
Bottom Bracket
BSO/Bike-Shaped-Object
Brifter
Cable Stretcher
Cable Pull
Cadence
Chain Gauge
Chain Tool
Chain Tug/Chain Tensioner
Chainstay Length
Chamois
Clipless Pedals
Crank
Derailer Hanger/Derailleur Ranger
Disc Hub
Door Zone
Dunlop Valve
Fender/Mudguard/Mudflaps
Fixed-Gear
Flip-Flop Hub
Frame
Folding Bike
Gear Inches
Groupset
Handlebars
Headset
Hose Clamp aka Jubilee Clip
Hub Skewer
Hub
Internally-Geared Hub
Lawyer lips/lawyer tabs
LBS/Local Bike Shop
Luggage Carrier/Rack
Master Link
Mixte
Mountain Bike
Pannier
Power Meter
Presta Valve/Presta Tube
Quick-Release
Rim
Saddle
Saddlebag
Schrader Valve/ Schrader Tube
Skewer
Spoke
Stem
Tire Lever/Tire Iron
Track Pump/Floor Pump
Triathalon Bars/Triathlon Bars

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4  
one term per answer would be beneficial –  dotjoe Aug 26 '10 at 13:51
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Should we add an "Anything not mentioned here" link? (With a link to sheldonbrown.com/glossary.html, of course.) –  jensgram Aug 26 '10 at 15:22
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Is there a way to link to a specific answer, so that in future questions you can use one of these terms and link to it for reference? –  Kevin Aug 26 '10 at 16:13
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Kevin: Under the bulk of the answer, there is a 'Link' hyperlink, which will link to the answer (its right above comment) –  Dan McClain Aug 26 '10 at 17:12
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@MarkIngram: useful things that aren't atually questions are what community wikis are for. –  freiheit Sep 12 '10 at 17:47
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53 Answers

Hub

One of the central parts of a conventional bicycle wheel. A hub is essentially a flanged metal tube (somewhat similar in shape to a spool of thread). The hub links the rim, axle, and (in the case of rear hubs) drivetrain of a bicycle:

  1. Rim

    Holes are drilled in the flanges of the hub so that the spokes may be threaded through the hub, which holds the "heads" of the spokes. The spoke nipples in the rim hold the other ends of the spokes. This is how the hub is connected to the rim.

  2. Axle

    The hub also has a lateral hole through which the axle is inserted. When the wheel is moving, the axle does not rotate, but the hub, spokes, and rim do. The axle does not contact the hub directly; the two components have a set of cups/cones, bearings, and locknuts holding them together, similar to headsets and head tubes. This is how the hub (and thus the rest of the wheel) is connected to (but rotates freely around) the axle.

  3. Drivetrain

    In order to provide a means by which the chain can rotate the wheel, rear hubs can have at least one cog attached. (Front hubs do not have any drivetrain components.) There several different types of rear hubs which accept various drivetrain systems:

Furthermore, some hubs (front and rear) are designed to accept disc brake pads, while some other hubs (rear only) have drum or coaster brake systems built-in.

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Folding Bike

AKA Folder

A bike that's designed to fold down to a small package without disassembly. They usually have smaller wheels, and are designed to be taken on trains and buses. Many transit organizations that don't allow bikes during peak hours will allow folding bikes during these busy times. They also reduce storage space requirements, often useful in city apartments.

There are also bikes that do not fold, but are designed to be taken apart easily, with frame latches, quick-release latches, or hybrid folding/unlatching systems.

Folding bike, ready to ride

Folding bike, ready to ride

Folding bike, in folded position

Folding bike, in folded position

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Bottom Bracket

The bottom bracket is the bearing assembly that the cranks attach to.

The bottom bracket shell is the part of the frame holding the bottom bracket.

Generally, bottom brackets are made for a specific size of bottom bracket shell and a specific crank attachment.

Traditional bottom brackets are a piece that goes inside the shell and has the ends of a spindle/axle coming out on each end (which the crankset attaches to), or possibly the cranks somehow attach into it.

There are also external bottom brackets where the bearings are outside the bottom bracket shell, and the cranks have a spindle that runs through to the other side. Typically the bottom bracket in this case is a hollow cylinder with a bearing assembly permanently attached on one side and a way to attach the bearing assembly on the other (once inserted through the shell).

Most recently, there are various new-style ("press-fit", etc) bottom brackets, that are designed like an external bottom bracket, but rely on having a larger bottom bracket shell and fit inside the shell. They still have the axle/spindle as part of the cranks.

Also note that there are eccentric bottom brackets, which are really a bottom bracket that goes inside of an offset bottom bracket shell that fits inside the frame's bottom bracket shell. This allows the bottom bracket to be moved a bit, to tension the chain on a single-speed or fixed-gear bike.

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Rim

The circular, U-shaped (in cross-section) part of a bicycle wheel that the tire and spokes are is attached to. Wheel-building is the process of attaching a hub to a rim with spokes; the name has connotations of smaller runs of wheels that are not machine-built, and are of presumably higher quality.

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Disc Hub

Disc hubs come in two varieties: 6-bolt ISO and Shimano's proprietary Centerlock spline. Converters exist to allow a Centerlock hub to accept a six-bolt disc rotor.

6-bolt ISO:

ISO disc hub

Shimano Centerlock: (Note, centerlock hubs ship with a rubber cover over the centerlock splines). Centerlock disc hub

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Hub Skewer

A replaceable part of a hub that attaches the hub/wheel assembly to the fork or frame. Some are equipped with a quick-release mechanism that allow removing the wheel without tools, facilitating changing a tire, putting a bike in the back seat of a car, etc. Unfortunately, the trade-off for easy wheel removal is that it's easier for thieves to remove a quick-release wheel.

enter image description here

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Chamois

The padding in a pair of bike shorts. Similarly, Chamois Cream is applied to the chamois to prevent chafing while riding.

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4  
And chamois cream is better known as "butt butter". –  Daniel R Hicks Jul 31 '11 at 18:24
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Frame

The frame is the skeleton of a bicycle. It's the part that all other parts are attached to. (Some parts, like the front wheel, are attached to other parts that are in turn attached to the frame.) The fork is sometimes considered a part of the frame, even though it's attached to the frame mechanically.

Frames are commonly made of steel, aluminum, carbon fiber, and sometimes more exotic materials suck as titanium or wood.

Aluminum mountain bicycle frame:

100_7864

Parts of a bicycle frame:

enter image description here

(Image from wikipedia; credit and legalese)

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Brifter

A combined brake and shift lever. Also referred to as integrated shifters.

brifter

Reference:

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Groupset

A groupset or gruppo (from the Italian for "group") generally refers to all of the components that make up a bicycle excluding the bicycle frame, forks, stem, wheels, tires, and rider contact points, such as the saddle and handlebars.

These parts typically include the following:

  • gear levers / shifters and brake levers or integrated brake levers/shifters
  • front and rear brakes (including calipers/pads or rotors/disks/pads)
  • front and rear derailleurs
  • bottom bracket
  • crankset
  • chain
  • freewheel or cassette

With the following forming part of some groupsets:

  • headset
  • assorted cables and cable housings

SRAM Red Groupset

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Headset

The group of bearings and bearing cups that allows the steer tube to turn freely within the head tube. Headsets come in two basic varieties.

Threaded headsets are common on older bikes and inexpensive bikes. They are called "threaded" headsets because the top race is held on with a threaded race and locknut.

Threaded Headset

Threadless headsets are standard on modern mid-level and high-end bicycles. They are called "threadless" headsets because there are no threads on the race nor is there a lock ring. The headset is held together by pressure created by a bolt through the top cap which threads into a star nut inside the steer tube.

Threadless Headset

Images courtesy of Sheldon Brown.

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Master Link

AKA: Breakable Link, Powerlink™

A link inserted onto a chain so that the chain can be broken and re-assembled without a chain tool. A set of pliers or a flathead screwdriver is usually sufficient to disassemble a chain with a master link.

More information at Sheldon Brown's site.

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Hose Clamp

A.K.A. Jubilee Clip

A ratcheting clamp often used to attach items to a bicycle fork or handlebars.

Flashlight attached to flat handlebars with a series of hose clamps.

Flashlight attached to handlebars with a series of hose clamps.

Jubilee Clip on Wikipedia

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1  
I see how the clamp goes around the torch, but how does it attach to the bars? Is there a second clamp, or does it twist around? –  Hugo Jun 20 '11 at 8:59
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Hose clamps can cut into paint an even metal if they're tight enough. You can stick a strip of old inner tube under the clamp to prevent this (and to provide better grip). –  naught101 May 12 '12 at 3:03
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Internally-Geared Hub

A setup where, instead of the cogs and derailleur mechanisms are on the outside of the wheel, they're sealed in the rear wheel's hub. As the gears are sealed away from water and road salt, internally-Geared hubs require much less in the way of cleaning than traditional drive-trains. These hubs are popular with commuters or other utility cyclists that will be ride in the snow and rain. They are also popular on folding bikes, as they are suited for bikes taken on crowded trains. When coupled with a single front chainring, IGH drivetrains permit the installation of a full chain guard, which most external gear systems don't allow.

Internal hubs are slightly heavier than comparable external drive-trains.

Hub

Reference:

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Spoke

The spokes connect the hub of a wheel to its rim. Spoke count is the number of spokes in a wheel, and a higher spoke count usually means a stronger wheel that can handle more weight and abuse.

Spoke tension (the force with which the spokes are tightened) can be adjusted individually. This is part of the process of truing a wheel, ensuring that tension is equally distributed in the wheel and that the rim is true, or straight. This is particularly important with bikes that have tight tolerances, but wheels that are trued are a benefit to any bike.

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Mixte

A mixte is a step-through (low top tube or "ladies") frame with 3 sets of stays instead of the usual two. The middle set of stays usually runs all the way to the head tube replacing the top tube, but on some mixte frames, the top tube is still a normal single tube. The traditional mixte has those axle-to-head stays straight, but there are also designs where they're bent to give an even lower standover height. They still retain the usual chain stays and seat stays. This design keeps the frame strong and doesn't require a longer seat post.

I believe the word itself comes from French and means "mixed" as in "mix of women's and men's styles" or maybe even "unisex".

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Cage/Bottle Cage/Bottle Holder

This is a mechanism to hold water bottles on a bike frame. They can be made of steel, aluminum or carbon. Most attach to the frame via preinstalled threaded holes, although on older frames an attachment that wraps around the entire tube was needed as an adapter. A couple examples of cages are shown:

Carbon Fibre Aluminum

For time trials and triathlons, there are also cage adapters that attach to the seat and provide mounting points for extra water bottle cages and spare tubes/inflators, and a few new mounts place a water bottle between the extension of an aerobar set.

Behind the seat Between the extensions

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What? No picture of the most ridiculously priced bottle cage? It's actually come down in price. I used to be around $300 a couple years ago. amazon.com/Campagnolo-Super-Record-Carbon-Bottle/dp/B009CH0NDQ –  Kibbee Nov 2 '12 at 19:24
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Mountain Bike

Often abbreviated as MTB.

A bike with sturdier wheels (usually 26" or 29") and wider tires - around 2" wide - meant for riding off-road.

Mountain bikes commonly come with only front suspension (hard tail), front and rear suspension (full suspension) or no suspension (rigid; also may be referred to as a hard tail). A rare configuration is the soft tail where only rear suspension is present.

Thicker frame tubing and flat handlebars are common features of mountain bikes.

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Power Meter

A power meter is a device on your bicycle to measure the power output of the rider.

enter image description here

Reference: Wikipedia

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Stack Height

The stack height of a headset is the vertical space taken up by a headset, and the stem when using a threadless headset. It's the difference between the headtube length and the fork steerer length needed to be able to use that headset with that fork and headtube.

http://www.parktool.com/blog/repair-help/fork-column-length-and-sizing

http://sheldonbrown.com/gloss_st-z.html

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Lawyer Lips/ Lawyer Tabs

Bicycle forks with quick-release wheel mechanisms are often equipped with these. The intent is to make it less likely that the wheel will accidentally release if the quick-release lever is used improperly.

lawyer lips (thanks to sk606 for the image)

In practice, they make it difficult to use the quick-release without unscrewing the skewer, making the quick-release harder to use.

These are named what the are because of the rumor that these were added to bikes for liability reasons.

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Cable Pull

When a brake or gear lever is moved it pulls on the attached gear or brake cable (for cable operated systems, at least). Since it's a lever, there are two related movements to consider. Cable Pull is how far the cable moves over the full travel of the lever. For brakes, there are two standards, short or conventional pull and long or V brake pull. For gears, there are a multitude of incompatible indexed gear options and few are compatible with each other.

cable pull diagram

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Chain guard/Chain cover

It's a frame, usually made of plastic or metal, that covers the entire length of the chain or only the upper part, mainly for protecting the rider from the dirt and lubricant on the chain, but can also protect the chain itself.

http://commons.wikimedia.org/wiki/File:Bike_chain_guard_full.JPG

http://upload.wikimedia.org/wikipedia/commons/thumb/6/69/Bike_chain_guard_part.JPG/320px-Bike_chain_guard_part.JPG

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