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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
1  
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

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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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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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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Track pump (or floor pump)

A large pump that you use by standing on the bottom plate and moving the handle up and down. You can use both hands and your back to pump a high pressure tire quickly and easily. Generally for use at home - or at the track - rather than for carrying on the bike. Some manufacturers make portable track pumps which bolt to the down tube for easier inflation of high pressure tires.

track pump

Features to look for:

  • sturdy construction
  • pressure gauge
  • a head that can be used with both Presta and Schrader valves
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Chain Tool or Chain Breaker

enter image description here

Used to 'break' a chain by punching out one of the link pins. Needed to shorten a new chain to the correct length or to replace a broken link.

A chain link is placed in the open slot and the handle turned to force a punch pin into the pin of the chain, pushing it out of the other side.

Traditionally the tool needed to be used quite carefully such that the pin would not pushed all the way out, as the same pin was later used to reassemble the chain, using the same tool. Obviously, if a chain is repeatedly "broken" and reassembled this way at the same link the pin and associated holes in the plates will wear and no longer hold well, so care must be taken to not do this.

More recently this strategy has changed somewhat. Shimano now supplies special replacement pins which are equipped with a break-off guide cone on one end, making it easier to reassemble the chain. (Even with this scheme one should still avoid repeatedly "breaking" and reassembling the chain at the same link, though.)

Several other manufacturers now sell what is commonly called a master link (or quick link), which allows a chain to be reassembled without tools.

enter image description here

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Flip-Flop Hub

Most often seen on fixed gear track (velodrome) bikes, a flip flop hub is hub that allows a cog to be attached to each side.

This allows a rider of a fixed gear bike to effectively 'change' gears by taking the rear wheel off, flipping it around and reattaching the wheel.

Track riders will use this to have a smaller (more teeth, fewer gear inches) warmup gear that allows them to spin at a higher cadence and a larger (fewer teeth, more gear inches) cog for racing or high speed efforts.

Variations of flip-flop hubs might offer a freewheel in one direction and a fixed gear in the other, so a cyclist can convert the bike from a single-speed to a fixed gear bike by flipping the rear wheel around.

The unused cog is an additional hazard. Many velodromes require unused cogs to be removed. A collision involving a bike carrying an unused cog at the 2013 North America Harcourt Bicycle Polo Championships led to an amendment of the NAH ruleset to explicitly identify exposed unused cogs as a prohibited hazard. Players are permitted to carry an unused cog if it is covered.

For a fixed-gear road cyclist, a flip-flop hub often is used to allow one side as a fixed gear, and the other side to freewheel. This way, a tired fixie rider can switch to freewheeling (possibly with a different ratio) and get home.

More information: http://en.wikipedia.org/wiki/Flip-flop_hub

alt text

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Clipless pedals

AKA clip-in or step-in

Clipless pedals are pedals that require a special cleated cycling shoe that locks the shoe into the pedal. Clipless refers to the pedal not having a toe clip. There are two major kind of clipless pedals, LOOK and Shimano Pedaling Dynamics (SPD). To release clipless pedals, the rider typically twists his/her foot.

Toe Clips

Clipless pedals are called clipless - even though you do clip onto them - because avoid the need for toe clips and straps. pedal with toe clip and strap

LOOK Pedals

LOOK pedals came first and were inspired by ski bindings. LOOK pedals are commonly used on road bikes. A similar (but not compatible) pedal system is Shimano's SPD-SL system.

LOOK Pedals

SPD Pedals

Shimano Pedaling Dynamics or SPD pedals use a cleat that is recessed into the shoe. This allows the rider to walk normally, which is why this pedal is commonly used with mountain bikes, where the rider may have to walk short distances over some obstacles. Note that Shimano's SPD-SL system is not compatible with SPD.

SpeedPlay Pedals

SpeedPlay Pedals

Crank Brothers 'Eggbeaters'

Crank Brothers Eggbeaters

This answer draws heavily from http://en.wikipedia.org/wiki/Clipless_pedals#Clipless_pedals

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1  
Added a link to clip+strap pedals, mainly to explain why clipless pedals have clips! –  mgb Feb 9 '11 at 5:20
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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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Bearing

A bearing is an interface between parts that turn and parts that do not. The hubs in the wheels contain bearings, as do the bottom bracket, the head tube, and the pedals.

Wheel bearing -- from Park Tool site

A standard bicycle wheel bearing consists of an axle, a hub, two cones, two locknuts, and a number of steel balls. In both ends of the axle is a concave section known as the "cup" that the balls sit in. The "cone", threaded onto the axle, contacts the balls from the other side, and together the cup and cone retain the balls and serve as the surfaces against which the balls roll.

The locknut secures the cone so that it doesn't thread in or out as the hub turns relative to the (stationary) axle.

The bearings in the bottom bracket and headset are similar except that the cup part is stationary and the axle turns.

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Derailleur hanger

The part of the bicycle frame that the rear derailleur screws into. It can be formed as part of the right rear dropout or can be a separate piece. Making the hanger a separate piece allows it to be made from a different alloy than the dropout and to be more precisely machined. Also, especially on inexpensive bikes, the separate hanger allows the same frame to be used in bikes with or without derailleurs. Although the separate hanger allows a damaged hanger to be replaced this is not the main intent of the arrangement.

Replaceable derallieur hanger

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I'm not sure I agree with the replacement ability not being a primary design point - for off road riding, it seems like this is key, especially on non-steel frames (e.g. aluminum), where the hanger cannot be safely bent back in cases of crashes due to metal fatigue. –  Batman Mar 17 at 7:02
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Fixed-Gear

AKA: Fixie

A fixed-gear bike has the rear gear locked to the hub, which fixes the pedals rotation to the rear wheels rotation. In other words, you can't coast: The pedals are always in motion as long as the bike is. Track bikes are commonly fixed-gear.

The sprocket is screwed directly onto a fixed hub. When the rear wheel turns, the pedals turn in the same direction. This allows a cyclist to stop without using a brake, by resisting the rotation of the cranks, and also to ride in reverse.

flip-flop hub on fixie setting

The hub in the picture is a flip-flop hub.

More information: http://en.wikipedia.org/wiki/Fixed_gear

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Gear Inches

One of the several ways to describe gearing; how hard/easy the bike is to pedal. The actual figure is the equivalent diameter of the wheel if you were on a direct pedal cycle like a unicycle or an old fashioned high-wheeler

Easier to pedal (granny-gears) have low gear inches (smaller equivalent wheel). Harder to pedal gears have higher gear inches.

The basic formula is:

GI = (CrT/CogT)*D
WHERE
GI     = Gear Inches
CrT    = Chain Ring Teeth
CogT   = Cog Teeth
D      = Wheel Diameter

For example, a 700c tire is going to have a diameter of roughly 26.3" (depends on the width of the tire). If you have shifted to your smallest front ring of 24 teeth, and your biggest rear cog of 27 teeth then your gear inches are:

GI = (24/27)*26.3 = 23.4"

Note: if you want to take the math a little further - and of course I do since I am a math nut - you can find how far you travel each pedal stroke by remembering that:

Circumference = pi*Diameter

In our example:

Circumference = 3.14*23.4" = 73.5

Note: you can search for Bicycle Gear Calculator and find several pages online that will do the math for you. There will be a lot of variation and calculators use different rounding and make different assumptions about wheel width. Pre-prepared tables are available, calculated for ETRTO 23-622 (700c x 23mm) tyres or in the case of traditional track racers' tables, a "standard" wheel with an assumed 27" overall diameter.

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Door Zone

The area next to parked cars that a suddenly opened door would cover. A hazard that you should avoid.

enter image description here

Satirical portrayal of Santa Monica bike lane design; it illustrates the "door zone" concept well.

Cycling in the Door Zone reduces your ability to react to hazards emerging from the space between parked vehicles. These may include unobservant pedestrians, inadequately restrained dogs (whose leads can reduce your options), sports equipment and children chasing sports equipment.

Drivers entering the road from a driveway, forecourt or junction are less likely to observe a cyclist who is not occupying the space where oncoming motor vehicles are expected to be observed. This contributes to the SMIDSY(Sorry mate, I didn't see you) phenomenon.

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Oh I see. I thought it was a good idea. –  Ambo100 Aug 9 '11 at 11:00
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BSO

Bicycle Shaped Object: A derogatory term for a very cheaply produced bike aleged to have very low quality components which can break when attempting to adjust them:

alt text

For instance the BSO pictured is being sold in the UK by ASDA (owned by Walmart) for £75. These bikes tend to be mass produced and sold in flat pack boxes which must be assembled.

As purchasers in this market may often be inexperienced or ignorant, many BSOs carry features which are included for marketing purposes but are unnecessary for the typical end-user. Such features may include front and rear suspension, wide off-road style tyres and an excessive number of gear ratios. Their inclusion reduces the budget available for other components and may not increase the BSO's functionality.

It is more advisable to search for a cheap second-hand bike in a similar price range from a more experienced cyclist or on eBay than to go for one of these.

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"An impassioned guide on why not to buy a cheap Bike or BSO" southcoastbikes.co.uk/articles.asp?article=NO_BSO –  Hugo Jul 17 '11 at 18:04
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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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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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Cadence

Cadence is the number of revolutions of the crank per minute.

Cyclists typically have a preferred cadence at which they feel most comfortable, and on bicycles with many gears it is possible to stick to a favourite cadence at a wide range of speeds. Recreational and utility cyclists typically cycle around 60–80 rpm; racing cyclists around 80–120 rpm and sprinters up to 170 rpm for short bursts. The professional racing cyclist and Tour de France champion Lance Armstrong is known for his technique of keeping up high cadences of around 110 rpm for hours on end to improve efficiency1

1 http://en.wikipedia.org/wiki/Cadence_(cycling)

If you are getting pain in your knees, it could be that your cadence is too low. A cadence between 80-100 will probably reduce knee pains, as stated in bicycling.com or more detailed at Cycling Performance Tips web site.

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We're really not here to copy and paste from Wikipedia. Are there recommended cadence rates for beginners? What users are generally concerned with cadence? Perhaps you could address concerns like these? –  Neil Fein Sep 2 '10 at 23:11
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Cable Stretcher

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

a

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

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I have never had problems installing brake cables with a standard set of pliers. –  Ian Sep 17 '10 at 9:22
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@neilfein, I tend to solder the ends of cables after I have cut them to stop any fraying. –  Ian Feb 9 '11 at 11:37
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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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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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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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Triathlon bars or Aerobars

Aerodynamic bike handlebars are for racing bicycles and particularly time trial bicycles.

Included are narrow, bolt-on extensions that draw the body forward into a tucked position, pursuit bars that spread the arms of the rider but drops the torso into a slightly lower position, and integrated units that combine elements of both designs.

Triathlon bars are commonly used in triathlons and time trial events on road and track. However, they are illegal in most mass start road races or any other event where drafting is permitted because, while aerodynamically advantageous, they tend to draw the hands away from brakes, make the rider slightly more unstable on the bike, and can be dangerous in the event of an accident. Further, they are not useful in sprints or shorter climbs where power is of greater importance than aerodynamics.

There is a distinct set of aerobars that are utilised in draft legal triathlons on regular road frames. As draft legal (ITU sanctioned) triathlon races require road frames that are UCI legal, a stubby pair of arms has been developed for this style of racing.

alt text

Sources:

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Stem

Attaches the handlebars to the bike, or, more precisely, to the steer tube (when using a threadless headset) or fork (when using a threaded headset). Many different sizes and angles of stems are available, so that the rider can place the handlebars where they will be the most comfortable during riding. There are also adjustable stems made, so the rider may change bar positions without removing the handlebars.

More information at Sheldon Brown's site

Adjustable stem

Adjustable stem on a touring bike, attached to the headset with risers, with the handlebars removed

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Quick-release

The term "quick-release" - often abbreviated as "QR" - usually refers to a quick-release axle, a device that allows the removal of a bicycle wheel without tools.

alt text

Quick-release axle

"Quick-release" also refers to several other types of quick-release mechanisms that are popular on folding bicycles, such as collapsible seatposts and folding frames.

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The quickness of the release is defeated on most bikes by extra lugs that force you to unscrew the axle almost fully to remove the wheel. They are supposed to stop the wheel falling out if the release comes loose - but they are really to stop you sueing and so are called lawyer-lugs –  mgb Oct 22 '10 at 3:51
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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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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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Chain Tug

AKA: Chain Tensioner

A device for use on bikes with horizontal dropouts, and normally with a fixed or single speed or hub gear. The chain tug(s) allow the chain tension and rear wheel alignment to be adjusted, and to stop the rear wheel from pulling forward while pedaling. Chain tug 1 Chain tug 2

Some chain tugs are available with derailleur hangers to allow horizontal droput bikes to run derailleur gearing systems.

enter image description here

More information about chain tugs is available in this answer.

Bottom Bracket mounted Chain Tensioners:
Typically seen on downhill styled mountain bikes.

Bottom Bracket Chain Tensioner Bottom Bracket Chain Tensioner on bicycle

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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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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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Brifter

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

brifter

Reference:

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