Terminology index - a list of bike part names and cycling concepts

Question

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

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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):

A mountain bike has the following parts (source):

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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.

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Contents:

Axle
Axle Nuts
BCD (Bolt Circle Diameter)
Bearing
Bonk/Bonking
Bottle Cage / Bottle Holder
Bottom Bracket
Brazed Frame
Brifter
BSO/Bike-Shaped-Object
Cable Pull
Cable Stretcher
Cadence
Chain Gauge
Chain Guard/Cover
Chain Tool
Chain Tug/Chain Tensioner
Chainstay Length
Chainsuck
Chamois
Clipless Pedals
Coaster Brake (foot brake / pedal brake)
Crank
Derailleur
Derailer Hanger/Derailleur Ranger
Disc Hub
Door Zone
Dropout
Dropper Post
Dunlop Valve
Fender/Mudguard/Mudflaps
Fixed-Gear
Flip-Flop Hub
Folding Bike
Frame
Gear Inches
Groupset
Handlebars
Headset
Hose Clamp aka Jubilee Clip
Hub
Hub Skewer
Internally-Geared Hub
Lawyer lips/lawyer tabs
LBS/Local Bike Shop
Luggage Carrier/Rack
Lugged Frame
Master Link
Mixte
Mountain Bike
Pannier
Play
Power Meter
Presta Valve/Presta Tube
Pump Peg
Q-Factor
Quick-Release
REI (Recreational Equipment Inc)
Rim
Rim Tape
Saddle
Saddlebag
Schrader Valve/ Schrader Tube
Single-speed
Skewer
Spider
Spoke
Stem
Suspension Fork/Rear Shock
Through/Thru Axle
Tire Clearance
Tire Lever/Tire Iron
Tire Saver
Track Pump/Floor Pump
Triathalon Bars/Triathlon Bars
Welded Frame

Answer 1

Brifter

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

Reference:

• Wikipedia

Answer 2

Cable Stretcher

A.K.A. "Fourth Hand" brake tool

The cable stretcher is used to stretch brake cables when installing brakes or new cable. It can also be used to tighten zip ties.

Answer 3

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:

(Image from wikipedia; credit and legalese)

Answer 4

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, in folded position

Answer 5

Chainstay Length

The chainstay length is measured from the center of the front chainring (centered on the bottom bracket spindle) to the center of the rear cog (centered on the rear axle). Frames with vertical rear dropouts will have a fixed chainstay length, while frames with horizontal or adjustable dropouts will have an adjustable chainstay length, as the wheel hub centre can be moved to different positions.

The chainstay length is typically measured directly from point to point but might be measured horizontally (parallel to the ground) which will give a slightly shorter value. If possible, check the geometry chart to see how it is defined.

Touring bicycles typically have longer chainstays to allow for more heel clearance when riding with panniers, but this comes at the cost of increased flex due to longer tubes. Bicycles designed for sprinting and for the track typically have extremely short chainstays.

There are formulae for calculating chain length, based on chainstay length and cog sizes, which are used in online chain length calculator.

Answer 6

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:

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

Some bicycle bags can mount to the frame's top tube, to the seatpost, or in front of the handlebars. These enable bikes without rack mounts to carry some gear.

Reference:

• Sheldon Brown's Bicycle Glossary: Rack

Answer 7

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. The axle is supported with bearings. Hubs have some key characteristics:

1. Number of holes

   Hubs are connected to the rim with spokes. Hubs will have a number of holes that matches the rim's drilling. For example, performance road bike wheels often have 20, 24, or 28 holes. Typically, the rear wheel is under more strain than the front, and rear wheels may have more spokes than front wheels.

   Some performance hubs are designed for straight pull spokes, where the spoke does not bend in a j-shape.

2. Axle type

   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.

   Axles can be quick release or thru axles. Quick release hubs all have a width of 9mm and a diameter of 100mm over the lock nuts at the front, and 130mm (road hubs) or 135mm (mountain bike hubs) at the rear. An increasing number of performance bikes are moving to thru axles. The diameters and lengths of thru axles vary more. Front thru axles come in widths of 15mm or 12mm. Rear axles tend to be 12mm. The Boost drivetrain standard for mountain bikes adds some width to both front and rear thru axles.

3. Drivetrain

   In order to provide a means by which the chain can rotate the wheel, rear hubs usually 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:

   • Freehubs. A cassette is mounted on the freehub body. The freehub body has splines. Note that there are several spline standards to take different types of cassettes. As an alternative, SRAM's XD driver takes cassettes that are threaded onto the driver body. Freehubs contain ratchets and pawls that will transmit torque when the rider pedals forward, but not when he/she pedals backward.
   • Freewheel-compatible hubs have threads to which a freewheel can be attached. Here, the freewheel contains the ratchets and pawls as well as the cogs. These are the predecessors of cassette hubs, and are no longer in wide production.
   • Internally geared hubs contain all the gears inside the hub. They don't have freewheels, but they do have an external cog to attach a chain or belt drive. These typically have higher drivetrain friction than (properly maintained) derailleur-based systems, but they are much more resistant to contamination.
   • Flip-flop, where a cog is mounted on either side of the wheel. According to legend, Tullio Campagnolo was inspired to develop the quick release skewer when he tried to flip a flip-flop hub secured by wingnuts in cold weather. This may be an anecdote.
   • Track/fixed-gear
   • Both front and rear hubs can accommodate electric motors. Users should be aware that they will change the bike's weight distribution and thus its handling. The batteries are mounted elsewhere on the bike. The crankset is an alternative area for mounting a motor.

4. Disc Rotor Attachment. For disc brakes hubs only, there are two standards governing how the disc rotor attaches to the hub. ISO or 6-bolt hubs mount the rotor with 6 bolts. For centerlock hubs, the rotor slides on to a splined interface, and a lockring secures it. This is irrelevant for rim brake hubs, where the rim is the brake rotor.

Miscellaneous characteristics: Hubs can come in a variety of finish options. They are usually black or silver, and may have matte or polished finishes. Aluminum hubs can be anodized in various other colors. A small minority of hubs are fully or partly made of carbon fiber. Additionally, some rear hubs can contain power meters. Front hubs can be equipped with dynamos to power lights or other electrical equipment. These add a small amount of drag even if the dynamo is off.

Answer 8

Saddlebag

(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.

Answer 9

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.

Answer 10

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.

(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.

For bikes with disk brakes they are properly promoted to the role of retaining ridges. Under braking loads the wheel tries to twist out of the dropouts and the ridges serve to prevent that.

Answer 11

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.

Image from Wikipedia

Answer 12

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).

Cranks have the following characteristics:

• Length: Common commercial cranks are typically in lengths of 165mm to 180mm in 2.5mm increments. 170, 172.5, and 175mm are the most common lengths. Cranks are generally sized by rider height or leg length.
• Chainrings: Cranks can accommodate 1 to 3 chainrings. 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 technology, such as a clutch rear derailleur and possibly a chain guide, aids 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.
• Chainring attachment: Many current cranksets have 5 or 4 arms, and chainrings are bolted to the arms. Some cranksets are direct mount, where the chainring(s) are integrated with the arms, and the assembly fits to a (usually) splined interface around the arms.
• 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 to 25mm diameter axles. Some third party cranksets have 30mm axles. These cranksets can fit any bottom bracket compatible with their axle diameter.
• Chainline: the distance from the center of the bottom bracket to the center of the chainrings or chainring. Typically, road double cranksets have a 43.5mm chainline. MTB cranksets have 50mm. 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.

• Miscellaneous: Cranks are typically made of aluminum. Less commonly, carbon fiber or titanium cranks exist. Aluminum cranksets are usually finished in silver or black, and higher end ones may have a polished finish. It is possible to paint a crankset, or to anodize aluminum or titanium cranksets for aesthetics. Some cranksets have power meters bonded to their arms, or they can accept chainring spiders with power meters integrated there. Cranksets can also connect to motors attached around the bottom bracket and/or to gearboxes mounted in the bottom bracket area.

• Sheldon Brown has more information on cranks.

Answer 13

Internally-Geared Hub

A setup where the hearing 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 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. They can also shift when the bicycle is completely stopped, unlike derailleur drivetrains.

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.

Reference:

• Sheldon Brown: Internal-Gear Hubs

Answer 14

Spoke

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 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.

Almost all spokes are made of steel. In performance bikes, spokes are sometimes bladed or ovalized, which reduces the wheel's air resistance slightly. Less commonly, spokes can be made from titanium or carbon fiber.

Answer 15

Rim

The circular, U-shaped (in cross-section) part of a bicycle wheel that the tire and spokes are is 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.

Characteristics

• Holes: rims are usually available in 4 hole increments. For example, rims for performance road bikes may be available in 20, 24, 28, or 32 holes. Rims for tandem road bikes may be available in 32, 36, or 40 holes. Some proprietary wheel systems had unusual numbers of holes.
• Material: most rims are aluminum. Older rims were made of wood or steel. Modern rims can be made of carbon fiber. Carbon enables much lower weight, and it makes deep aerodynamic wheels more practical (the rims would be heavy in aluminum).
• Braking surface: rims for rim brake wheels have a brake track. It may be machined smooth or not. Rims for disc brakes do not have a brake track. Carbon rims for rim brakes may have special material in the brake track to enhance braking. For rim brakes, carbon rims perform more poorly than aluminum rims, especially in the rain.
• Tire bed: Most rims fit clincher tires. High-performance rims at the time of writing can usually fit tubed or tubeless clincher tires. Alternatively, rims can fit tubular tires, which are glued to the rim bed. Tubular tires do not fit on clincher rims, and vice versa.

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. Wear due to braking is not an issue with disc brakes, as that is borne by the disc rotors.

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.

Clincher rims require tape on the rim bed.

Answer 16

Welded Frame

A frame made by melting the tubes it is built from at the joins, typically with a similar metal added as filler. Mass produced aluminium and steel frames are almost all built this way as with modern machines it is very fast and cheap.

Answer 17

Hose Clamp

A.K.A. Jubilee Clip

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

Flashlight attached to handlebars with a series of hose clamps.

Jubilee Clip on Wikipedia

Answer 18

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".

• http://www.sheldonbrown.com/gloss_m.html#mixte
• http://en.wikipedia.org/wiki/Step-through_frame#Mixte

Answer 19

Brazed Frame

see also lugged frame and welded frame

A method of joining steel 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 steel, 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.

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

This contrasts with welding, where the parent metal is melted and the same or a very similar metal is added as filler.

Answer 20

Chamois

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.

Answer 21

Bonk

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.

Glycogen is a form of glucose that our bodies use as fuel. It is stored in the muscles and liver. Athletes bonk when they deplete their muscle glycogen stores. 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. Carbohydrate loading before an event may also make bonking less likely.

Answer 22

Thru Axles / Through Axles

These axles secure your wheels to the frame and fork. Historically, bicycles have used quick releases that clamp the dropouts. However, the forces generated by disc brakes can cause wheels to come out of the dropouts if the quick release is not secured properly. Thru axles are an alternative. They insert into the dropout on one side, and they thread directly into inserts in the fork and frame on the other side.

A Through Axle has no dropouts - as this image shows there is a solid line of white metal from the fork all the way around

Contrast with Quick Release

The purported advantages are:

• Increased stiffness when turning
• Shock load is shared between both fork legs more evenly
• Less rotational torsion on the fork leg with the brake caliper attached.
• Thicker axles are harder to break - a 15mm axle has more strength than a 9mm QR.
• Thru axles enable more consistent placement of the wheel compared to dropouts and quick releases. Because disc brakes have tight tolerances, it is possible to insert the wheel such that the pads are rubbing on the disc rotor in a quick release setup.

Answer 23

Spider

The part that connects the cranks to the chain rings. Typically spiders have 5 legs, but 3, 4, and six legs are also common.

Answer 24

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.

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

Answer 25

Dropout

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 mountain bikes the axles pass through holes at the end of the forks.

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.

The image below shows a Colnago horizontal dropout in a Surly frame; a typical example. It has adjustment screws and an integral derailleur hanger.

Front dropouts are vertical, and some rear dropouts are also vertical.

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.

Answer 26

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). A rare configuration is the soft tail where the frame has a small amount of compliance or some basic rear suspension built-in.

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

Answer 27

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 per shift. 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.

Answer 28

Lugged Frame

also lugs

A method of frame-building where at least the major joints consist of frame tubes inserted into castings (the lugs). For steel frames, lugs are hand-made by bending and filing rather than casting. Lugged frames are normally brazed, but can also be soldered (with lead or silver rather than brass) and occasionally glued (the Windcheetah trike used glued aluminium, for example). Historically this was very common, and many classic steel frames were built this way. Today with better welding technology it's rare, especially in mass produced bikes. Another alternative construction method for steel frames is fillet brazing.

A minority of carbon frames are lugged, for example the Colnago C-64 (link from Cyclingweekly), or some custom carbon frames. Here, manufacturers bond carbon tubes to lugs. The alternative to lugs in carbon frames is monocoque construction, where the frame is molded in one or two large pieces. It is harder to customize monocoque frames due to the costs of building the molds.

Lugged construction with dissimilar materials is possible but more rare. For example, the Trek 2300 frame used carbon tubes bonded to aluminum lugs.

Answer 29

Cage/Bottle Cage/Bottle Holder

Water bottle cages hold water bottles on a bike frame. They can be made of steel, aluminum, carbon, or titanium. 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 gravel bikes have a third mount on the underside of the down tube. Some full suspension mountain bikes may have only one mount, as the suspension system can take up some room in the bike's main triangle. Some dedicated cyclocross racing bikes may lack cage mounts entirely, as cyclocross races are short and one may need to shoulder the bicycle during a race.

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, although this will void your warranty and it will create a stress riser. This raises the risk of later failure. It may not be an issue with relatively thick steel tubing, however.

A couple examples of cages are shown:

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.)

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.

Answer 30

Power Meter

A power meter measures your power output for training purposes. For example, riders might target interval training at a certain percent of their functional threshold power. This discussion on StackExchange outlines what power meters are and why cyclists, mostly those interested in serious competition, might want one. Power meters are ubiquitous in professional road racing at the time of writing.

Power meters can be mounted in various places on the bike. Note that the companies listed below are examples and are not product recommendations, nor are the lists exhaustive.

1. The chainring spider. SRM, a German company, may have been the first company to make power meters, and they made spider-based power meters. Power2Max and Quarq (owned by SRAM) are other companies in this category. Power2Max focuses on cranksets which have removable chainring spiders. Quarq makes their own cranks instead.
2. The rear hub. Not long after SRM, Powertap introduced hubs that measured power. To the writer's knowledge in 2019, they're the only such company in this category.
3. One or both crankarms. Here, a strain gauge is bonded to the crankarm(s). To the author's recollection, these came later than the first two categories, with Stages being an early example. Pioneer and 4iiii are two other companies. Infocrank designed a full crankset from the ground up, with strain gauges mounted internally.
4. Pedals. Yet other companies have placed strain gauges in the pedal spindle, e.g. Garmin (they bought a company called Metrigear), Favero Assioma, Powertap. Brim Brothers, which is now defunct, were testing a version that measured at the pedal-cleat interface. Most power pedals at the time of writing are based on the Look Keo road pedal system, possibly due to patent protection of Shimano's SPD (mountain) and SPD-SL (road) systems.
5. The crank spindle. Easton/Race Face and some models of Rotor cranks have spindle-based power meters. This type of power meter is relatively rare at the time of writing.
6. The above 5 categories can be called direct force power meters (DFPMs), because they directly measure power (actually torque and cadence). One other type of power meter estimates power from air resistance, but this requires some assumptions (e.g. rolling resistance from your tires, drivetrain resistance). These units may be able to work independently to estimate power, or else they could work in conjunction with a a direct force power meter to estimate your aerodynamic drag coefficient. The Velocomp PowerPod can be a standalone power unit. The Notio Konnect appears to only work in combination with a DFPM.
7. Off the bike, power meters may be integrated into stationary trainers. Most smart trainers measure power directly, at the trainer's resistance unit. Without a smart trainer, it is also possible to estimate power using the bike's current speed if the resistance unit's resistance curve is known (i.e. the amount of resistance generated for a given speed).

Power meters in categories 3, 4, and 5 can either: a) directly measure each leg's power, or b) measure only one leg's power, usually the left, and estimate total power by doubling that. b) is obviously cheaper, but it can be less accurate. Riders with a known leg imbalance (e.g. after an injury) may want to take note of this issue.

Power meters in category 1 and 2 directly measure your total power from both legs. They may be able to estimate each leg's contribution through algorithms. Some have criticized this estimation as potentially inaccurate.

Last, power meters actually measure both torque and cadence separately, and calculate power from those two parameters. They measure torque through strain gauges. They measure cadence through magnets and reed switches (more rare) or accelerometers. Both processes have some level of inaccuracy. For example, InfoCrank issued a white paper (dated 2017) arguing that cadence measured through magnets is more accurate than via accelerometer (but they have updated their power cranks to measure cadence via accelerometer or magnets).

Reference: Wikipedia