This question and its answers list the names of bike parts and cycling concepts.

Some Rules

  • Make sure you only put one term per answer!
  • Try to include an image if applicable
  • Include sources that contain detailed information
  • Add a link to the index in this question using edit.

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.)

A road bike has the following parts (source):

enter image description here

A mountain bike has the following parts (source): enter image description here

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.

Actuation Ratio
Axle Nuts
BCD (Bolt Circle Diameter)
Belt Drive
Bottle Cage / Bottle Holder
Bottom Bracket
Boom/Boom Tube
Brazed Frame
BSD (Bead Seat Diameter)
Cable Pull
Cable Stretcher
Chain Gauge
Chain Guard/Cover
Chain Tool
Chain Tug/Chain Tensioner
Chainstay Length
Clipless Pedals
Coaster Brake (foot brake / pedal brake)
Derailer Hanger/Derailleur Ranger
Direct Drive
Disk/Disc Brake
Disc Hub
Door Zone
Dropper Post
Dunlop Valve
Dutch Bike
Electronic shifting
Flip-Flop Hub
Folding Bike
Foot Peg
Frame Sizing
Gear Inches
Hose Clamp aka Jubilee Clip
Hub Skewer
Internally-Geared Hub
Keel Tube
Lawyer lips/lawyer tabs
Lateral Tube
LBS/Local Bike Shop
Luggage Carrier/Rack
Lugged Frame
Master Link
Mountain Bike
Over Locknut Dimension or OLD
P-clip or R-clip
Potts Mod BMX Brakes
Power Meter
Presta Valve/Presta Tube
Pump Peg
Recumbent Cycles
REI (Recreational Equipment Inc)
Rim Tape
Rim Brakes, e.g. cantilever, dual pivot, V-brakes
Schrader Valve/ Schrader Tube
Shaft Drive
Stack and Reach
Stay, Mudguard/fender
Suspension Fork/Rear Shock
Through/Thru Axle
Tire, Clincher
Tire, Tubeless
Tire, Tubular
Tire, Solid/airless/runflat
Tire Boot
Tire Clearance
Tire Lever/Tire Iron
Tire Saver
Tire Sealant
Track Pump/Floor Pump
Triathalon Bars/Triathlon Bars
Welded Frame
  • 8
    One term per answer please - would be beneficial.
    – dotjoe
    Commented Aug 26, 2010 at 13:51
  • 1
    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
    Commented Aug 26, 2010 at 16:13
  • 2
    Kevin: Under the bulk of the answer, there is a 'Link' hyperlink, which will link to the answer (its right above comment) Commented Aug 26, 2010 at 17:12
  • 8
    @MarkIngram: useful things that aren't actually questions are what community wikis are for.
    – freiheit
    Commented Sep 12, 2010 at 17:47
  • 2
    This page could use some more love. Maybe if people keep linking to individual terms here, more people will know about this page. Commented Jun 27, 2011 at 2:39

101 Answers 101



Also called the seat, the saddle is where the rider sits.

enter image description here

Gel saddle

enter image description here

Leather saddle

enter image description here

Plastic saddle


Tyre Saver

Small loop of wire attached so that it rubs continuously on the tyre as it rotates. This brushes off debris and reduces the number of punctures. These were popular mainly in the 1970's and 1980's, with the advent of lightweight puncture-resistant tyres they have almost disappeared.

tyre saver

  • Good work Mσᶎ. I think we also called them stone pickers or tire pickers, but my recent research only found stone picking machines to remove stones from farmland.
    – andy256
    Commented Jun 10, 2014 at 3:41

Frame or frameset

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.) A frame plus a fork are often called a frameset. The frameset's geometry determines the bike's handling characteristics.

Frames are usually made of steel, aluminum, carbon fiber, or titanium. Less common frame materials include bamboo, other types of wood, or magnesium alloy.

Aluminum mountain bicycle frame:


Parts of a bicycle frame:

enter image description here

(Image from wikipedia; credit and legalese)


Rack, aka Luggage Carrier

A rack is a frame attached to a bicycle to provide space for a pannier or other type of pack to be attached. Not all frames and forks are built with rack mounts. Racks can be mounted at the rear of a bicycle, for example on the touring bike below: enter image description here

Or front racks mount to the fork, as shown in a photo from Cyclingabout.com:

enter image description here



Disc Hub

Disc hubs are designed to mount disc rotors. Rotor mounts 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

You cannot mount a disc rotor on a non-disc hub. You can use a 6-bolt rotor with a groupset that is otherwise designed for centerlock rotors or vice versa.

  • Most Rohloff hubs are also "disk hubs", and come with a proprietary 4 hole mount. No adapter is possible, the reason they do this is because they need a bigger hole than the other mounts allow.
    – Móż
    Commented Jan 14, 2017 at 6:09


A combined brake and shift lever. May be called integrated shifters. On road bikes, “shifter” may be understood to include the brake lever as well, but this is not true for mountain bikes. The specific term may be more common in the UK than the US. The image below shows a Campagnolo brifter for road bikes.




Hub Skewer

A metal rod with a clamping mechanism that attaches the hub/wheel assembly to the fork or frame. Many skewers 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. Skewers without a quick release will use a hex or Torx wrench for removal. It is also possible to secure the wheels with axle nuts, many of which use a crescent wrench of appropriate size.

enter image description here


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


Master link

Also known as:

  • Quick link
  • Breakable link
  • PowerLink™ (made by SRAM)
  • MissingLink (made by KMC)

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

Master link pliers are available to open a master link. Note that not all designs of master link are sold as suitable for re-use.

More information at Sheldon Brown's site.

enter image description here

Image from Wikipedia


Internally-Geared Hub

A setup where the gearing mechanism is sealed in the rear wheel's hub, away from water, road salt, and other contaminants. 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 who frequently ride in 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. They can also shift when the bicycle is completely stopped, unlike derailleur drivetrains. Gearboxes are related, and they put the gears in the bottom bracket area.

Internal hubs are slightly heavier than comparable external drive-trains. They also have greater drivetrain friction than a well-maintained external drivetrain.

They will typically require oil to lubricate the gears, which can be injected through a port.





(a.k.a. seat bag, wedge bag, etc.) Small bag designed to be attached to the underside of a bicycle saddle, usually large enough to hold tools to change a flat tire.

The name "saddlebag" is often mistakenly applied to panniers which resemble saddlebags used on motorcycles or horse saddles.

  • also known as a wedge-bag/pack
    – mgb
    Commented Oct 22, 2010 at 3:52

Spider (part of the crankset)

The part that connects the crank arms to the chain rings. You bolt the chainrings to the spider. In the past, you merely needed to find chainrings appropriate to your transmission (e.g. 8 speed, 9 speed) whose bolt circle diameter matched the spider. Many end 11 and 12 speed cranksets have moved to 4-arm asymmetric designs, so you will need OEM replacements or chainrings that are designed to mate with the specific crankset.

Historically, most spiders have had 5 legs, and the crank arms and the spider were forged or molded (for carbon cranks) as one piece. With some cranks, the spider may be constructed separately, or the crankset may use chainrings that incorporate a spider. In either case, the spider or chainring would mount to a splined interface at the base of the crankarm.

Image from trekstorecolumbus.com

Some cranks use direct mount chainrings. Here, the spider is a part of the chainring, and the crankarms have a splined interface. This is discussed more on the article on cranks.

  • 2
    Note: the study of spiders is Arachnology :-)
    – andy256
    Commented Jul 15, 2015 at 2:27
  • Two suggestions: make the entry logically consistent, and add the apparently missing words. If my name is to be attached to such bosh then it looks like it's time to delete my account.
    – andy256
    Commented Nov 12, 2021 at 2:34

Crank, aka chainset, crankset

We turn the pedals and cranks with our legs. Pedals screw into threads at the end of the crankarms. The cranks themselves are, in turn, attached to the bottom bracket. Gearing is controlled by the size of the front chainring(s).

Some key concepts:

  • Length: Cranks have traditionally been available in lengths of 170mm, 172.5mm, and 175mm, with many manufacturers now offering shorter or occasionally longer lengths too. Mountain bikers riding long-travel bikes and triathlon cyclists may have started this trend of using shorter cranks.
  • Chainrings: Cranks are usually designed for use with between 1 to 3 chainrings, although 4-ring designs have existed historically. The chainrings control the gearing available to the bicycle. 1x systems with a single front chainring (pronounced "one-by") are common on mountain bikes and gravel bikes. They frequently have teeth specially designed to retain the chain (e.g. narrow-wide chainring). Other technologies such as a clutched rear derailleur and possibly a chain guide aid chain retention also. 2x systems are common on road bikes, and have pins and ramps to guide the chain to the large ring. Triple chainrings were once standard on MTBs. They may be more common on older touring bikes also. Front derailleurs are typically specific to triple or double chainrings.
  • Bolt circle diameter: determines what sizes of chainring can attach to the crankset. Some cranksets use direct mount chainrings instead, which are secured to a splined interface at the crank arm. Different manufacturers have different spline patterns, and bolt patterns may vary too despite the BCD value.
  • Bottom bracket attachment or axle type: Cranksets may be designed to mate to a specific bottom bracket, in the case of square tapered, older Shimano Hollowtech, or ISIS cranksets. Alternatively, cranksets may be designed around a specific axle type. For example, Shimano, SRAM, and Campagnolo use 22.00 to 28.99mm diameter axles. Some third party cranksets have 30mm axles. Bottom brackets are not necessarily inter-compatible despite being designed for the same spindle diameter, so be sure to check with manufacturer guidelines. Note: some “24mm” FSA cranks are actually 24.07mm and will not readily fit standard 24.00mm bottom brackets.
  • Chainline: the distance from the centre of the bottom bracket to the center of the chainrings or chainring. Typically, road double cranksets have a 43.5mm chainline. Non-boost MTB cranksets are around 50mm, but wider chain lines are available for boost and super boost bikes. The advent of disc brakes on road and gravel bikes has led to some cranksets with 45mm chainlines. Front derailleurs are designed for optimal performance on a specific chain line. Mixing a road front derailleur with a 45mm chainline crankset may work, but it may not be optimal. Mixing a road derailleur with a 50mm chainline is very unlikely to work.
  • Maintenance: The cranks themselves don’t typically require maintenance, but the chainrings will wear eventually. Typically, they will outlast the cassette.


  • Cranksets can also connect to motors attached around the bottom bracket (on E-bikes) and/or to gearboxes mounted in the bottom bracket area.
  • Sheldon Brown has more information on cranks.

[Crank arms](https://flic.kr/p/nyQzv4)



The circular, U-shaped (in cross-section) part of a bicycle wheel that the tire and spokes are attached to. Rims attach to the hubs with spokes. Wheel-building is the process of attaching a hub to a rim with spokes, including bringing the spokes up to tension.

With rim brakes, the rim's braking surface will eventually wear out. The metal will become dangerously thin, and it may crack, as this image from Sheldon Brown's site shows. Some rims have a dimple in the sidewall as a wear indicator. When the wear indicator is no longer visible, replace the rim. Otherwise, check for concavity by holding a ruler to the rim. The photograph below was originally posted to the Bike Radar forum and it depicts a rim due for replacement. Wear due to braking is not an issue with disc brakes, as that is borne by the disc rotors.

enter image description here

This image shows a worn rim that has cracked.

enter image description here


  • If you ride in the wet with rim brakes, it is good to clean off your rims and brake pads afterward, as the grit from the road will abrade your rims.
  • Rims can come out of true, i.e. they will wobble side to side or up and down (the latter is sometimes called being out of round). They can be trued by adjusting the spoke nipples. Tightening a nipple increases the spoke's tension, which pulls the affected rim segment in the direction of the spoke. Wheels, especially mass produced ones, do not always come true from the factory. Most cyclists get a bike store to do this, but you can true your wheels at home with a spoke wrench and, preferably, a truing stand. You can use the frame and/or your brake pads as a makeshift stand, but commercial ones are available.
  • If an aluminum rim gets bent in a crash, it can often be straightened. This is less necessary on disc brake wheels that are not being set up tubeless.
  • If you must replace a rim due to a crash, consider if reusing the hub is more economical than buying a new wheel. If the damaged wheel does not use proprietary spokes or rim drilling patterns, you are not limited to replacement rims from the original manufacturer. Make sure to match the number of holes in the old rim to the new one. Old spokes are generally not reused, and a different rim will require different length spokes anyway. A bike store can help you determine the spoke lengths that are needed. Some examples of major rim manufacturers with a wide range of price points are DT Swiss, Velocity, and Kinlin, although there are numerous others.


Buyers comparing rims or complete wheels (often called wheelsets) may be interested in the following characteristics.

  • Size: Rims are often given a nominal size. The formal way to measure size is the diameter at the bead seats, in millimeters. 700c road bike wheels and 29" MTB wheels share the same BSD of 622mm. These are the most common wheel sizes in these disciplines. The Bead Seat Diameter article, linked earlier, has more discussion.

  • Internal width: this is the width measured between the bead hooks if present, or the inner faces of the sidewall if the rim is hookless. All else equal, the same tire will be wider on a rim with wider internal width. Internal widths have grown much wider over time for both road and mountain bikes. External width is sometimes listed, but it is arguably less important unless you’re trying to maximize aerodynamics (here, you ideally want your tires to measure narrower than the external width).

  • Tire types and hooked or hookless: Tubeless-compatible rims can fit tubed or tubeless clincher tires. You can run a tubeless clincher with a tube inside. Older clincher rims may not accept tubeless tires, so check that a rim explicitly indicates tubeless compatibility if this is important. More rarely, rims can fit tubular tires, which are glued to the rim bed. At the time of writing, many MTB wheels and newer road wheels, especially carbon ones, are hookless, meaning that they don’t have bead hooks. Not all clincher tires are compatible with hookless rims, so make sure your tire explicitly states this. Hookless rims are easier and cheaper to construct in carbon. Tubular tires do not fit on clincher rims, and vice versa. Tubulars are extensively used in professional road racing, and they are typically safer to run if punctured than clinchers, but you have to be able to prepare and glue the tires (or pay someone to do so).

  • Holes: Relevant if replacing a rim or having a wheel built. Fewer spokes means slightly more aerodynamic wheels, although the differences are small. Rims and wheels for performance road bikes may be available in 20, 24, 28, or 32 spokes, with 20 spokes typically only being available for front rim brake wheels. Rims for tandem road bikes tend to have more spokes.

  • Tire widths: You can mostly mount whatever width of tire you want on the rim. This discussion has more information on what width of tires are compatible with rims. However, the frame's tire clearance is more likely to be the limiting factor than the rim. Some aerodynamic wheels will specify what tire widths are optimal to maximize aerodynamics. Some rims may explicitly state a minimum width. Check the manufacturer website for details.

  • Aluminum rims are extruded as a bar, then rolled into a rim. The ends of the bar are pinned together, held together by a sleeve, or welded. Pinned rims are generally the cheapest. Carbon rims are made in one piece in a mold. They can be made lighter than aluminum rims of the same depth. A deep, aerodynamic aluminum rim would be very heavy. Carbon rims for rim brakes generally have poorer braking than aluminum rims, although rims and brake pads have improved.

Clincher rims require tape on the rim bed to cover the holes that are used to insert spoke nipples. A few clincher rims may not have these holes, and the manufacturer will explicitly say if this is the case.


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. It is thought that these were added to bikes after a lawsuit, which explains the name's origin. Professional cyclists would frequently file these off, as they may need to change wheels quickly during a race.

Disc brakes impose asymmetric torque on the hub, and they may cause skewers to be ejected from dropouts. Lawyer lips help prevent this. However, bikes with disc brakes now overwhelmingly use thru-axles, which physically can't be ejected by torque.



The spokes connect the hub of a wheel to its rim. Spokes are secured to the rim by a spoke nipple. They insert into the hub at its flanges. 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 the rim does not wobble side to side or up and down. This is particularly important with bikes that have low tire clearance, but wheels that are trued are a benefit to any bike.

Almost all spokes are made of steel. In performance bikes, spokes are sometimes bladed or ovalized, which reduces the wheel's air resistance slightly.



The padding in a pair of cycling shorts. Traditionally this was made using chamois leather but is now usually a synthetic material.

Chamois cream can be used to prevent chafing while riding. With chamois leather, it can dry out and stiffen, so chamois cream is applied to the chamois to keep it supple. Modern chamois creams, however, are designed to be applied to the rider themselves rather than the synthetic padding.

  • 6
    And chamois cream is better known as "butt butter". Commented Jul 31, 2011 at 18:24

Mountain Bike

Often abbreviated as MTB. A bike with sturdier wheels (usually 29" or 27.5") and wider tires - at least 2" wide - meant for riding off-road. They are also characterized by flat handlebars, which offer better control in very rough terrain than drop bars, and they almost always have suspension. Modern MTBs also have very different frame geometry than road bikes, tending towards relatively upright positions.

Mountain bikes commonly come with front suspension (hard tail) or both front and rear suspension (full suspension). (Rigid) MTBs without any suspension do exist, and they require much more careful choice of lines. In the past, soft tail MTBs had a small, low-travel suspension where the seatstays joined the frame.

  • Any MTB riders able to improve this or the suspension article? I am unfamiliar with MTB subtypes, but they could be helpful to list. On suspension, I tried to list key concepts but am not certain if all were described correctly.
    – Weiwen Ng
    Commented Dec 3, 2021 at 23:56

Mixte, Step-Through Frame

A mixte is a frame with 3 sets of stays instead of the usual two. Riders don't have to raise their legs far to get them over the top tube. These frames were an advantage to women wearing dresses. The image below is courtesy of Sheldon Brown's site.

enter image description here

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.

Wikipedia notes that the word mixte may come from the French word for mixed (as in mix of women's and men's styles) or unisex.


Welded Frame

A frame made by melting the tubes it is built from at the joins, typically with a similar metal added as filler. For steel bikes, welding is more amenable to mass production than brazing or lugs. Aluminum and titanium bikes have typically not used either of the other methods, although some frames have carbon tubes bonded to metal lugs. Welding is typically done under an inert gas. Framebuilders must prevent contamination at the welds from oxygen or other materials. If this is not done, the weld can fail later on.

welded frame joints


Cage/Bottle Cage/Bottle Holder

Water bottle cages hold water bottles on a bike frame. Most cages attach to the frame via preinstalled threaded holes that are usually called bosses or mounts.

Most modern frames have at least two bottle cage mounts, one on the seat tube and one on the down tube. Some bikes, especially gravel bikes, have a third mount on the underside of the down tube. However, full suspension mountain bikes may have only one mount, as the suspension system can take up some room in the bike's main triangle.

On frames without mounts, bottle cage adapters might be able to strap around the tube. Alternatively, you may be able to drill a hole into the frame and put in a threaded insert called a riv nut. On metal frames with thicker tubing, this is likely to be safe, but it does create a stress riser which may later fail, and it will void any warranty.

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. A few new mounts place a water bottle between the extension of an aerobar set. (Image credit to Slowtwitch.com, a triathlon forum.)

Behind the seat Between the extensions

Hydration vests like those made by Camelbak are an option for bikes without any cage mounts or to carry additional water. These may be less comfortable in hot weather. Hydration bladders can also be carried in frame packs that are strapped to the top tube; these packs frequently have exit ports for the hoses. Last, stem bags will strap to the stem and handlebar, and these can carry a bottle also.

Some bikes, mainly gravel bikes, may have mounts on the outsides of the fork blades. These multipurpose mounts can fit standard bottle cages or larger cargo cages. Some gravel and triathlon bikes may have a pair of bosses on the top tube near the stem. These may have the spacing typical of water bottle cages, but they are used for bolt-on boxes (aka Bento boxes) that hold snacks and equipment.



In the context of bicycles dropouts are a kind of fork end, where the wheels are attached. Dropouts are employed on most bikes; on some bikes the axles pass through holes at the end of the forks (through-axles).

We often use dropout for any slot to hold the axle at the end of forks, but strictly speaking, a dropout is a fork end where the wheel can be removed from the frame without taking the chain off first. It's called a dropout because after loosening the quick release or nuts the wheel will drop out when the bike is lifted off the ground. It is much quicker and easier to remove wheels with the bike the right way up than when the bike is upside down.

All front dropouts are vertical, and are usually also accompanied by lawyer tabs to mitigate the risk of improperly closing the quick release skewer. Most rear dropouts are as vertical. However, older bikes often have horizontal dropouts. The image below shows a Colnago horizontal dropout in a Surly frame; a typical example. It has adjustment screws and an integral derailleur hanger. Colnago horizontal dropout in a Surly frame

This image (CC BY-SA) from Wikipedia shows a fork end that is not a dropout. The wheel cannot be removed without removing the chain.

fork end


Dropper Posts

Dropper posts are more commonly found on mountain bikes and on some gravel bikes. They allow the rider to quickly lower their saddle height, and thus their center of gravity. This is useful for very steep descents, where you might otherwise feel like you are going over the handlebars. You actuate the dropper using either a remote lever mounted on the bars or an actuator under the saddle (entry level models).

They are also appearing on upper versions of electric urban (e-)bikes, where they offer other benefits: easier to get in and out the saddle or to share a bike between people of different heights.

Cable-operated and hydraulic-operated designs exist. The cable or hose can be routed either internally or externally to the frame (as the frame allows). For mountain bikes, a small release lever is fitted to the handlebar. For gravel bikes, the left brifter can be used for the the dropper post (1x transmissions only). SRAM's AXS system can actuate a dropper post wirelessly, usually from the the left shift paddle.

dropper post
(source: evanscycles.com)

  • 1
    Maybe we don't need to list manufacturers in these wikis, we can't list them all and makes can go obsolete, we want the entries to be as enduring as possible
    – Swifty
    Commented Sep 25, 2019 at 10:31
  • Excellent! Want to add an entry for "seatpost" too? We don't have one listed. Could be worth adding why a MTB rider might want to lower their saddle, without stopping.
    – Criggie
    Commented Sep 25, 2019 at 10:32
  • I concur with Swifty, and I’ve deleted the manufacturer list. If others disagree, I can revert. I changed the entry on power meters to delete the list of manufacturers I added, but for historical interest i mentioned SRM, the first company to make a commercial power meter. If there’s interest in that sort of history here, I would vote for adding that.
    – Weiwen Ng
    Commented Nov 16, 2021 at 16:38
  • Imagine rocking up two years late for an edit :D
    – Lucero79
    Commented Nov 19, 2021 at 13:21

Pump Peg

A pump peg is a small protrusion on a bike frame which is intended to facilitate the mounting of a "frame pump". Depending on the style of the frame, the peg may be positioned to allow the pump to fit on the underside of the top tube (of a standard diamond frame) or on the trailing side of the down tube. The peg is designed to mate with a corresponding hole in the end of the pump. The pump is spring loaded, and the expansion of the spring holds the pump in place.

Some schemes have a peg at each end, while others rely on the other end of the pump being wedged into the V formed by the top tube and seat tube.

enter image description here

enter image description here


Power Meter

Power meters measure your power output. Power can be used to pace a ride, and to do structured interval training. This StackExchange question has more in depth discussion. Power meters are ubiquitous in professional road racing. They have enabled better talent discovery and better and more targeted training. They can benefit many amateurs, but they are not required for satisfactory progress.

Alternatives include training by heart rate or by perceived effort. That said, heart rate will take several seconds to respond when you start an interval, and it will likewise take several seconds to come down when you stop an interval. Heart rate can be affected by fatigue. Some of the same criticisms hold for perceived effort. Power overcomes those disadvantages.

For structured training, riders estimate their functional threshold power (FTP). This is the maximum power you can sustain for some time, usually 30-70 minutes, and this usually corresponds to blood lactate levels (indicating anaerobic energy production) being steady as opposed to rising. Riders design intervals based on their FTP, e.g. warm up, ride 2x 15 minutes at 94-100% of FTP with a 7 minute rest, then cool down. More information on training zones (by FTP and heart rate) is here. Riders usually re-estimate their FTP during their season to keep their power targets in the correct zone.

A brief history and basic technical information

Power meters use strain gauges to measure the amount of deflection or torque in a bike component, usually the crank or the pedal spindle, as you pedal. They also use a cadence sensor. Power = torque * cadence. This answer has more detailed information on how power meters work physically. They transmit this information wirelessly to a computer, typically over Bluetooth or a sport-specific protocol called ANT+. The data files can be analyzed by a coach and uploaded to a training site like Strava. Note that power meters require a computer capable of communicating via ANT+ or Bluetooth to work, which is an additional expense. The older PowerTap shown below had a proprietary computer, but all current power meters work with most bike computers that have ANT+ or Bluetooth capability.

The first power meters were made by SRM (Schoberer Rad Metrik, a German company), and they were very expensive. As with many electronic goods, they have declined substantially in price in recent years. SRM power meters replaced the chainring spider, and several other power meters are still mounted here. Later power meters were mounted in hubs (e.g. PowerTap, now owned by SRAM, pictured below), the crankarms, or the pedal spindles, or a few less common arrangements. E-bikes also measure torque, a component of power, to determine how much assistance to provide.

Image of power meter

It is preferable to measure the total power generated by both legs, but some manufacturers offer left-only power meters to save costs. Power meters mounted at the crank spider, the hub, or on both crankarms or pedals will measure a rider's total power. Left-only power meters can be placed on the left crankarm or pedal spindle, or even on the right side. Left-only power is less accurate than total power. Also, if you have two independent power sensors on each side, you can measure the power balance between left and right, but it isn't clear if this is a significant benefit versus just knowing total power.

Power also enables virtual cycling environments like Zwift, where you simulate a rider's progress through a course and interactions between multiple riders based on their power and other inputs. Additionally, smart trainers can vary resistance at the flywheel to simulate gradient. Traditional wheel-on trainers can be used in this environment as well, but they can't simulate gradient. They can be used without a power meter, but this is less accurate.


Power meters are sealed units. They don’t suffer wear in the same way that chains, cables, and other bike components do. If replaceable, the batteries will need to be replaced periodically. The strain gauges are delicate. Manufacturers will try to protect the strain gauge pod, but users should also take as much care as possible not to knock the pod unnecessarily.

Power meters may need to be periodically zeroed, like taring a weighing scale. You do this from your head unit or the phone app. Many newer power meters can auto zero. If you suspect a power meter is still reading wrongly, another step may be to calibrate the slope, I.e. the change in resistance with a known weight. This is usually done at the manufacturer, although some power meters enable users to do this. Smart trainers have a spindown function that is equivalent.

Smart trainers contain drive belts and cartridge bearings. These might wear out. Both belts and bearings tend to come in standard sizes. You could take the worn belt in to an auto parts store. For bearings, you can measure the physical size of the bearing; see the entry on bearings for more information. Removing them may take specialized tooling.

Reference: Wikipedia

  • @DanK I was thinking that SRM was a German company, and some wires got crossed in my head, and I made the rather amusing typo about Metrigear being a country that you caught. Thanks!
    – Weiwen Ng
    Commented Sep 27, 2019 at 14:04

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

  • 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
    Commented Jun 20, 2011 at 8:59
  • 1
    There's a second clamp. Commented Jun 20, 2011 at 14:14
  • 12
    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
    Commented May 12, 2012 at 3:03

Cable Pull

Many brakes and most derailleurs are actuated by pulling cables. Cable pull is how far the cable moves when the brake lever is pulled, or a shift lever is actuated.

For brakes, there are two main standards, short or conventional pull and long or V brake pull. Road bikes have tended to use short pull levers, although current Shimano road brakes operate on a slightly different cable pull than other brands. For mountain bikes, cable-actuated brakes have tended to use long pull. This means that mountain bike V-brakes will not work correctly with road levers and vice versa, although cable pull adapters may be available.

For indexed gears each groupset manufacturer will specify its own cable pull per shift (i.e. each click at the shifter), as well as how far the derailleur travels laterally per shift (i.e. the shift ratio or actuation ratio). Thus, shifters and derailleurs cannot generally be mixed across component manufacturers. Non-indexed (friction) shifters can generally be mixed, provided they have enough total cable pull.

cable pull diagram

  • Sorry about the edit war. Short pull brakes are not Shimano specific, friction shifters work if there's enough cable pull.
    – Móż
    Commented Nov 5, 2019 at 4:14


An expression used by cyclists to describe sudden fatigue or loss of energy while exercising. Also known as crashing, blowing up, or running out of steam/gas/fuel, or empty tank. The phenomenon applies to all endurance sports. In running, it may be called hitting the wall. Bonking is distinct from merely being tired due to lack of sleep or from a higher than normal training load. Subjectively, it can be quite unpleasant to bonk! There can be cognitive effects as well as physical ones.

Athletes bonk when they deplete their muscle glycogen stores. Glycogen is a form of glucose (a simple carbohydrate) that our bodies use as fuel. It is stored in the muscles and liver. This can be reversed by eating immediately, preferably foods high in easily-digestible sugars. Water alone will not reverse a bonk. Bonking can be prevented entirely by eating regularly during a race or training, although this is generally not a concern in sessions under 2 hours. Carbohydrate loading before an event may also make bonking less likely. During an event, you can consume carbohydrates in sports drinks, in pre-made energy chews, gels, or bars, or via real food.

  • You've edited out the point that this is an unpleasant result; an experience to be avoided wherever possible. Its more than simply being tired.
    – Criggie
    Commented Oct 21, 2019 at 18:38

Brazed Frame

see also lugged frame and welded frame

A method of joining frame parts together by melting brass into the joins between frame tubes. Frames can be fillet brazed or use lugs, which are extra, normally cast metal, parts that the frame tubes slot into before brazing. Lugs make building a strong frame easier, provided you have exactly the right lug for the situation. Fillet brazing offers more freedom but also more skill is required to produce a strong joint. Some people think that there is an aesthetic benefit over welding, as brazing, like some welding techniques, do not leave a rough bead of material at the joints.

Shown is part of a fillet brazed steel frame, with the grey steel contrasting with the copper-coloured brass.

fillet brazed frame

The most common alternative method is welding, where the parent metal is melted and the same or a very similar metal is added as filler. Welding is generally stronger, faster and can be automated but brazing or soldering are sometimes preferred for DIY or aesthetic reasons.


Thru Axles / Through Axles

Through axles (TAs) are large-diameter threaded fasteners that secure the bike's wheels to the frame and fork, serving the same role as Quick Release Skewers. They originated on mountain bikes because QR axles were occasionally breaking during extreme riding, and the forces generated by disc brakes can cause wheels to come out of the dropouts if their quick release is not secured properly. Since then, they have been used on many road bikes too.

Thru axles insert into the dropout on one side, pass through the hub's hollow axle, and then thread into female threads on the fork and frame on the other side. A frame and fork must be designed to use thru axles, and you generally can’t retrofit a quick release frame to take TAs (with the exception of some frames that use modular/interchangeable dropouts.)

The through axle is the upper device in the following image:

from http://cdn.mos.bikeradar.imdserve.com/images/news/2014/02/14/1392416431992-ecxclyd8c6n5-700-80.jpg

The dropouts on a through axle frame or fork are "closed" as opposed to the "open" dropouts used by QR systems — as this image shows, there is a solid ring of metal surrounding the black thru axle and threaded insert.

From http://fcdn.mtbr.com/attachments/beginners-corner/789715d1365723144-need-help-new-bike-assembly-thru-axle-axle-pic.jpg

Contrast with Quick Release


The purported advantages of thru axles are:

  • Increased stiffness when turning because of the larger diameter hub interface and higher clamping force. They can also be stronger in shear as they are no longer restricted by the 9 or 10mm diameter of a QR open dropout.
  • Thru axles enable more consistent placement of the wheel compared to open dropouts and quick releases. Because it is possible to secure the wheel askew in the dropouts in a quick release setup, brake rub may occur due to the misalignment because disc brakes have tight tolerances regarding alignment. The repeatable nature of the closed dropout system minimizes this issue.
  • Torque from braking can no longer eject the front wheel because the axle is encapsulated by the dropouts.
  • Shock load is shared between both fork legs more evenly.
  • Less rotational torsion on the fork leg that the brake caliper attaches to.

Replacing a Thru Axle / Sizing

As of today (2021), through axle diameters are as follows:

  • 12mm for rear wheels
  • 12mm for road bike front wheels
  • 15mm for XC/trail/enduro mountain bike front wheels
  • 20mm for downhill mountain bike front wheels

Exceptions are common though, such as 15mm front TAs on earlier thru axle road bikes.

Unlike quick releases, thru axles tend to be unique to each bike. Two bikes may have the same over-locknut distance (e.g. 142mm for road bikes), but their dropouts are likely to differ in thickness. The thread pitch is also a variable (the spacing between adjacent thread peaks, e.g. 1 or 1.5mm). Some suspension designs such as Trek's ABP necessitate extra-long axles as well. Do not try to use axles differing from the intended specifications to avoid damaging one's bicycle and potentially incurring personal injury.

Riders can get replacement thru axles from the bike's manufacturer, fork manufacturer, or from aftermarket brands. Specifications to be aware of include:

  • Diameter
  • Total length
  • Length of the threaded portion
  • Thread pitch

Retention Mechanism

Through axles are available with a variety of retention methods. These include hexagonal tool fittings for use with Allen wrenches, integrated handles, detachable handles, cam levers (much like those on QRs), and specialty designs such as Cervelo's RAT system. Additionally, forks and frames may have extra features such as pinch bolts that further secure the through axle. Each design balances a different ratio between security, stiffness, weight, sleekness (handles can catch on trail debris), and convenience, so it is up to the rider to decide what design works best for them.

Final Notes

Note the distinction between through axles and the threaded axles often found on childrens' and utility bicycles. While both have large-diameter threads, threaded axles are integral to the hub, while through axles are entirely separate from the fork and frame. Additionally, threaded axles use open dropouts, unlike the closed dropouts used by TA designs. Lastly, threaded axles are tightened using separate nuts, while TAs are tightened directly into the frame or fork.

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