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


Bicycle-Shaped Object (BSO)

A derogatory term for a very cheaply produced bike with very low quality components. The components can be hard to maintain due to poor tolerances. BSOs are often sold at non-specialty retail stores.

The etymology of the term is uncertain. It appears in use in some parts of the English-speaking world. It may originate in the UK, as discussed at the link. Other languages may use terms equivalent to supermarket bike or department store bike. These terms are likely to be understood in English as well.

example BSO

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 for self-assembly.

Purchasers of lower-end bicycles tend to be less experienced cyclists who focus on price. 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. For cyclists who are riding on city streets or smooth trails, these features are unnecessary. Including these features reduces the budget available for better components elsewhere.

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.

  • I softened the language a bit. I agree with you about BSOs, but the situation isn't quite that clear -- and people do occasionally tour on them. (I'll try to dig up a link for that last.) Commented Sep 17, 2010 at 4:18
  • 7
    "An impassioned guide on why not to buy a cheap Bike or BSO" southcoastbikes.co.uk/articles.asp?article=NO_BSO
    – Hugo
    Commented Jul 17, 2011 at 18:04
  • 4
    Suspension - it's not just that it's unnecessary for typical users, but that cheap suspension will add weight and absorb pedalling energy for little or no benefit. (An unpractised rider on pot-holed roads may well benefit from wide tyres though, if not knobbly ones). Also, the typical bike shaped object is heavy, being cheap steel tubes which are both large (to imitate the look of better aluminium frames) and thick-walled (to compensate for cheap steel with cheap welding being weaker). The one illustrated is far from the worst available.
    – armb
    Commented Feb 11, 2015 at 14:19

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.

  • I've never seen this before in the UK. Interesting.
    – Ambo100
    Commented Aug 8, 2011 at 19:09
  • @Amb100: you've never seen a bike lane that ran through the area doors would open into? The "DOOR LANE" thing isn't real, but the configuration of bike lane in door zone is common in the US.
    – freiheit
    Commented Aug 8, 2011 at 20:29
  • 2
    Oh I see. I thought it was a good idea.
    – Ambo100
    Commented Aug 9, 2011 at 11:00
  • 1
    Also known as the death zone. As a rider goes slower, they're more likely to be riding closer to the kerb and parked cars. Faster riders tend to move out more and into the traffic lane.
    – Criggie
    Commented Dec 6, 2015 at 22:48

Presta Valve / Presta Tube

aka Sclaverand valve (SV) or French valve

alt text

The Presta valve is a valve commonly found in high pressure road style and many mountain bicycle inner tubes. The air pressure in an inflated tire holds the inner valve body shut. A small screw and captive nut on the top of the valve body permits the valve to be screwed shut and ensure that it remains tightly closed. The nut must be unscrewed to permit airflow in either direction (this must be done before attaching a pump). The screw remains captive on the valve body even when unscrewed fully; it is tightened again after the tire is inflated and the pump removed.

Presta valve photo credit

Photo sequence of removing the dust cap then unscrewing the nut so the valve is ready to inflate.

A Presta valve adapter can be used to fill a Presta tube with a normal Schrader-style air pump, although many pumps today come with a built-in adapter.

For a video tutorial on the use of the adapter, check out this video at BicycleTutor.com

More information: Presta valve (Wikipedia).

Go to Schrader valve.
Go to Dunlop valve.



LBS is the acronym commonly used for Local Bike Shop. The term is usually used when comparing small, privately owned shops with big box or department stores, or with internet-based bicycle retailers. In the UK and Ireland, the expression Independent Bicycle Dealer (IBD) is also used.

The best local bike shops usually have trained staff who have many years of experience in selling, maintaining, and repairing bicycles and have a well-equipped repair workshop. They can special order parts and let you know if a modification you want to make will work -- and how to make it work. They also can serve as hubs for the local cycling community, connecting riders to other riders. As with all things, local bike shops vary in terms of their experience and attitude. It pays to shop around to find a LBS that matches your interests and orientation, e.g. more casual cyclist, touring cyclists, competitive cyclists.

Large department or chain stores, on the other hand, often sell low-quality bikes (aka BSOs). Their staff usually have little to no background in bicycle mechanics. Thus, they may not properly assemble the bikes, and they usually cannot repair or maintain the BSOs they do sell because they do not have the skills to do so. Your only recourse may be to just return the whole bicycle to the store if it is still under warranty.

Internet bicycle retailers often have lower prices than LBSes due to economies of scale. However, it is harder to get service and support there.

http://www.flickr.com/photos/johnprolly/5728618798/ http://www.flickr.com/photos/johnprolly/5728618798/



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.

EDIT by Ivor

To answer a comment below on beginners and cadence...

Cadence is critical to enjoying your cycling and if you become involved in cycle racing, winning. Cadence is something that is learned and once learned you promptly forget about it and move onto getting other things right :)

For a beginner:

  1. Get to know your gears.
    • Drop it into a high gear (big chainring on the front, small cog on the back)
    • Feel how hard it is to push (Pay attention to where you feel the muscles working)
    • Drop it into a low gear (smallest chainring on the front, largest cog on the back)
    • Feel how free your legs spin (Pay attention to how you bounce in the saddle :) If you are bouncing, then you are spinning too much, i.e. your cadence is too high)
    • Find a combination of gears that allow you to spin your pedals without feeling undue pain in your muscles and doesn't make you feel out of breath. (Ignore the speed for the moment)
    • Get to know this "sweet spot", ride around in this gear for a while and adjust your gears to suit your speed so that you balance not being out of breath and over exertion. (Watch out for the bounce in the saddle :) )
  2. The next thing to take into account is how fast you want to go
    • Without a bike computer? - Your feeling of relative speed is good enough
    • With a bike computer? - Set a reasonable target, say 20 km/h
    • Using the gears you have selected for your sweet spot, try to hit your target speed.
    • Once you hit it, can you keep it going? For how long? - Set a reasonable target say 5 mins.
    • When you have finished this, where does it hurt?
    • In your chest? Out of breath big time? - You may have been spinning too much, i.e. your cadence was too high?
    • Muscles in the small of your back, quads, glutes, knees, calves groaning or hurting (not burning, burning isn't as bad as you think) - You may have been spinning too little i.e. your cadence was too low?
  3. There is an ideal cadence proposed by some sports physiologists that is somewhere between 80 to 100 turns of the pedal per minute (rpm)
    • The only way to know your cadence accurately is to have a cadence enabled bike computer and sensor.
    • The other way is to know your gear ratios (Check out BikeCalc.com)
    • For example, You are riding your bike, it has a wheel of size 700c/29 and a tyre that is 23 mm wide, with a front chainring of 34 teeth, a rear cog of 17 and you are pedalling at a speed of 20 km/h. You should then have a cadence of 79 rpm. Simples :) (Get the bike computer ;) )
  4. Get used to spinning your legs in that range of RPM, i.e. 80 to 100 rpm.
    • In all conditions, on any terrain, whatever the occasion.
    • It trains your heart and body to be cardio fit and with a stronger heart comes better stamina and greater strength.
    • Pick up the pace and work to get the legs spinning at the next level of speed.
    • Hard work and worth it.
  5. Go cycling with a group more experienced than you
    • Watch them as they cycle, see all of the different styles and high cadence
    • Listen to the experienced guys as they can advise on many many things.
  6. Enjoy it, you will have earned it :)
  • 9
    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? Commented Sep 2, 2010 at 23:11
  • 5
    I'm not sure that citing Lance Armstrong as an example is really useful, given that he achieved his performances through doping...
    – mac
    Commented Apr 26, 2014 at 19:53
  • @Ivor my reading of your edit is that it's not clear if bouncing on the saddle is good or not. Can you make that clear please?
    – andy256
    Commented Jan 11, 2015 at 4:33
  • 1
    @andy256 I have taken your comments on board and modified the edit. Bouncing is definitely not good. The Quote I used to differentiate the text and have now removed it as the text is my own ramblings on cadence and I am the only one who would claim it :)
    – Ivor
    Commented Feb 11, 2015 at 10:31

Clipless pedals a.k.a. clip-in or step-in pedals

Clipless pedals require a special cleated cycling shoe that locks itself into the pedal's surface. To release a foot/shoe from a clipless pedal, the rider typically twists his/her foot outwards. These were inspired by ski bindings.

Before clipless pedals, riders used rigid shoes with flat (also called quill) pedals and toe clip straps, as pictured below. The term "clipless" refers to not needing the toe clips. However, it is confusing because riders "clip in" to the pedals. Alternatively, flat pedals are an option for riders not willing to use clipless pedals or toe clips. On MTBs, flat pedals typically have retaining pins for grip.

pedal with toe clip and strap

A clipless pedal was patented as early as 1895 by Charles Hanson, as documented on Wikipedia's article on clipless pedals. Speedplay, a relatively niche pedal maker that is relatively popular in triathlon, maintained an online museum that was taken down since its acquisition by Wahoo. They contend that (link to archive.org) Cinelli may have released what Speedplay called "the first modern-day clipless pedal" in 1970. Look, a French company that manufactures road bikes and components, may have been the first to release a widely recognized and adopted pedal system. Their corporate history contends that they developed ski bindings, and translated that system to road cycling. Wikipedia documents that Bernard Hinault won the Tour de France in 1985 on Look pedals. An example of LOOK pedals is below.

LOOK Pedals

LOOK pedals came first and were inspired by ski bindings. LOOK pedals are commonly used on road bikes. A similar (but incompatible) pedal system is Shimano's SPD-SL system.

Subsequently, Shimano appear to have adapted clipless pedals to mountain bikes. Notably, MTB shoes have tread, and MTB pedals have generally developed to be able to clear dirt and mud. Cycling shoes are compatible either with road (3 bolt mounting system) or MTB shoes (2 bolt mounting system), although a handful are compatible with either.

Shimano SPD

There are multiple companies manufacturing road and MTB pedals. Road cyclists often perceive that road pedals offer a bigger and more stable platform than MTB pedals. MTB pedals and shoes are objectively easier to walk in. There is nothing wrong with choosing to use MTB pedals on a road bike. In the reverse case, road pedals are often unable to engage if contaminated by dirt or mud.


  • You need to choose a fore-aft position for the cleats. It is common practice to start with the cleats under the ball of the foot. Some riders prefer to have their cleats further back than this. Rearward positions may be better for endurance riders or long slow distance rides. Some sprinters may prefer their cleats further forward. All shoes have some range of fore-aft adjustment, although some makes may have less adjustment than others.
  • Most cleats have float, I.e. you can rotate your heel left or right, usually by a total of about 2-3 degrees in each direction. This accounts for the fact that we tend not to point our feet straight ahead. For road shoes especially, you can rotate the cleats to account for this. There are guides on how to do this on YouTube, but a bike store will be able to help you. If you feel like you want to rotate your foot further but it is at the limit of the pedal, you should seek help.
  • Some cleats have zero float or very low float (e.g. black LOOK and red Shimano SPD-SL cleats). Most casual cyclists should avoid these. If you decide otherwise, you need to pay attention to cleat rotation to avoid knee problems.
  • Cleats will wear and require periodic replacement. Highly active riders might replace them yearly, maybe more. Rubber cleat covers can help reduce wear while you’re walking on road cleats. However, clipping and unclipping does wear the cleat. If your cleats are worn, it will feel like the pedal is gripping your shoe sloppily, and there may be play in unexpected directions (e.g. up/down). The picture below is from Shimano’s SPD-SL cleat manual and shows the wear indicators in the cleat.

enter image description here

  • Aren't TIME pedals kind of major? I see a lot of them (and I own a pair), but it might be some kind of local phenomenon...
    – dee-see
    Commented Oct 14, 2010 at 23:26
  • @domsterr: Feel free to edit this answer Commented Oct 15, 2010 at 11:27
  • 2
    Added a link to clip+strap pedals, mainly to explain why clipless pedals have clips!
    – mgb
    Commented Feb 9, 2011 at 5:20
  • Would platform pedals qualify as well, since they are 'clipless' too?
    – Ehryk
    Commented Sep 28, 2013 at 3:51
  • I don't have the ability to edit (or the knowledge) but I'd encourage a bit of expansion here with shoes/cleats. See: bicycles.stackexchange.com/questions/20700/…
    – Ryan
    Commented Mar 12, 2014 at 13:13

Fixed Gear or Fixed Wheel

AKA: Fixie

A fixed-gear bicycle 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.

Fixed-gear bikes are almost always single-speed (i.e. have only a single gear ratio), but internal-gear hubs without freewheels do exist.

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

Compare with Single Speed.

  • 3
    One should note that typically, horizontal dropouts are required to convert a bike from derailleur to fixed gear, since a pulley cannot be used as a chain tensioner (when you resist to brake, the pulley will be sheared off the bike). Vertical dropouts can be adopted in some cases using something like White Industries' Eccentric Rear Hub or an eccentric bottom bracket or something.
    – Batman
    Commented Mar 17, 2014 at 6:53

Schrader valve/Schrader tube

aka "American valve" or "car valve" or "Auto valve" (AV)

alt text

The Schrader valve consists of a valve stem into which a valve core is threaded, and is used on virtually all automobile tires and most wider rimmed bicycle tires. The valve core is a poppet valve assisted by a spring.

A valve cap is important on a Schrader valve because if one is not fitted, dirt and water can enter the outside of the valve, potentially jamming it or contaminating the sealing surfaces and causing a leak. Rock salt and other chemical deicers used in the winter are especially damaging for the brass components in the Schrader valve.

Schrader valves are almost universal on car tires, meaning you can often (carefully) inflate your bike tires with the air machines at roadside garages.

For an instruction video on patching and inflating a Schrader tube, check out this video on BicycleTutor.com.

More information: http://en.wikipedia.org/wiki/Schrader_valve
Go to Presta Valve.
Go to Dunlop valve.

  • 2
    I don't think it would hurt to combine this one with its sibling answer Commented Sep 6, 2010 at 17:51
  • @Joe - Except that it makes linking to one valve or the other more difficult. Commented Nov 2, 2010 at 15:06
  • 3
    In the UK at least this can also be referred to as the 'car type' since it's common to our car tyres. It's quite useful to use this type of valve because it means you can get your tires pumped up at petrol stations. Commented Mar 3, 2011 at 17:24
  • 1
    What are the advantages/disadvantages of this type of valves? Do they loose more air with time? (compared to presta) Are they heavier? Easier to find pumps for it?
    – J.A.I.L.
    Commented Feb 16, 2013 at 15:19

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



A pannier, pronounced pan-yer /ˈpanyər, ˈpanēər/ (US) or pan-i-er /ˈpanɪə/ (UK) [1], is a bag designed to be mounted on the side of a bicycle rack. Bags can be made of nylon, canvas, or waterproof materials such as PVC. Panniers are most commonly carried on the rear, but smaller panniers intended for a front rack are also available.

enter image description here

Often erroneously called a saddlebag because a pannier on a motorcycle or horse is attached to the saddle. On a bicycle, the saddlebag mounts behind the rider from loops at the back of the saddle. The saddle bag goes athwartship – from side to side.

Bikes that do not have rack mounts can often accept bags that strap under the handlebars, under the top tube, and behind the seatpost. Gravel bikes often do not have rack mounts, and these alternative bags are used instead. Potentially, these may affect a bike's handling more than a rack and panniers would, because the loads are carried higher on the bike.

  • How do you pronounce this? pan-near, panny-air, pan-near? Commented Sep 6, 2010 at 17:54
  • I pronounce it pan-yay, but I'm not sure how to properly say it. Commented Sep 6, 2010 at 18:36
  • 6
    It's an English word that's commonly mistaken for being a french word. It's pronounced "PAN-yer", but many people say "PAN-yay".
    – freiheit
    Commented Sep 12, 2010 at 18:04
  • @freiheit - The link you put in allows for two pronunciations, I updated this entry. Commented Oct 22, 2010 at 14:34
  • 4
    @freiheit: It's an English word that is also a French word. That's like saying "Paris" is an English word that's commonly mistaken for a French word. In English, we pronounce "pannier" as "PAN-yer" and "Paris" as "PAIR-iss" but in French they are pronounced "Pan-YAY" and "Pa-REE."
    – R. Chung
    Commented Nov 2, 2012 at 19:03


Quick release skewers (sometimes abbreviated QR, sometimes just called skewers) secure bicycle wheels in the dropouts. They have a lever that when opened, enables the wheel to be removed quickly and without additional tools. They use a cam mechanism at the lever end pulling against a threaded nut at the other end. The cam mechanism may be internal or external; the latter type is cheaper to produce and is often lighter, but it produces lower clamping force for the same amount of hand pressure on the QR lever.

Wheels with disc brakes may be secured by QRs or by thru axles. Disc brakes generate a lot of torque at the hub. Some experts contend that disc brakes can eject wheels from dropouts. Thus, most current disc brake bikes and wheels use thru axles.

If you are replacing a quick release, you may need to take note of the length of the rear QR. Mountain bike hubs for quick releases have had a length of 135mm over the locknuts, compared to road hubs’ 130mm. If a QR is road specific, it may be listed as 130mm. An MTB QR can be used on a road rear hub. It will have a bit of extra axle protruding, but this does not interfere with anything. If a QR is simply listed as “rear”, it is probably suitable for MTBs. Front road and MTB QRs are 100mm long.

a picture of a bicycle front wheel quick release assembly
Quick-release axle (internal cam)


Their invention is frequently attributed to Tullio Campagnolo, the founder of the eponymous component manufacturer. Jan Heine's research shows this may be inaccurate. Heine was unable to determine who invented the QR, as there appears to be no original patent for the QR mechanism. Campagnolo was certainly one of the first companies to mass produce a high-quality QR.

Tabs called lawyer lips frequently come on fork and/or frame dropouts. They prevent the wheel from dropping out immediately when the QR lever comes open, the nut must be unthreaded several turns as well. These tabs increase the amount of time needed to operate a QR but they can be an important safeguard against improper operation of a QR.

QRs are sometimes used on seatpost clamps as well, to allow easy adjustment of the saddle height. "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.

Last, non-quick release skewers exist, often for security purposes. These are loosened on one side with hex wrenches or similar implements. They are similar to axle nuts.

  • I know there are some different kinds of quick release. Some have a spring in there to make it easier right? Maybe explain those differences Commented Sep 6, 2010 at 17:55
  • 3
    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
    Commented Oct 22, 2010 at 3:51
  • 2
    @Martin - I think the value of a quick release isn't that it's fast so much as that you don't need a wrench to get the wheel off. Commented Oct 22, 2010 at 4:12
  • Well, Tullio Campagnolo's design (which forms the basis of a modern QR skewer) was designed for race conditions, so the speed value exists. I've never heard lawyer lugs, but I have heard lawyer lips. In most cases, however, the primary value is the lack of tools (which does make it relatively faster).
    – Batman
    Commented Mar 17, 2014 at 6:55
  • and of course in cities like NY you don't want to have a quick release on your wheels because they will get stolen.
    – Deesbek
    Commented Nov 28, 2016 at 3:09

Triathlon bars or Aerobars

Aerodynamic handlebars are used extensively on triathlon, time trial, and track bikes, and sometimes in long-distance racing or riding on the road. The position on the extensions reduces the rider's frontal area considerably.

The picture below shows a full aerodynamic bar setup used on a dedicated bike. Shifters are mounted on the extensions, and brake levers on the base bar. One can also buy clip-on bars for standard road bikes. This type of bar would also be used in draft-legal triathlon races.

They are illegal in mass start road races because the aerodynanmic position has the rider's hands away from brakes, and the narrower arm stance makes the rider slightly more unstable on the bike. These factors reduce control.

alt text


  • Are tri-bars purely aerodynamic or do they adjust your riding position enough to relieve muscles you will use in the run part of a triathlon?
    – mgb
    Commented Feb 9, 2011 at 5:20
  • Remember Greg Lemond final time trail in the Tour de France 1989. Closest TDF win ever! youtube.com/watch?v=AyvwtOQYQ-E Thank you earobars.
    – allcaps
    Commented Apr 14, 2014 at 12:08
  • @mgb It might be that triathlon bikes in general are designed for a more forward position (steeper seat angle). This is thought to make you use your hamstrings more, whereas you may need your quads for the run. I'm not sure if that contention is backed up by research! forum.slowtwitch.com/forum/Slowtwitch_Forums_C1/…
    – Weiwen Ng
    Commented Nov 12, 2019 at 19:19

Tire Lever

aka Tire Iron

A tire lever is a small, narrow lever used to help lift a tire off a rim. Traditionally they were steel, later aluminium alloy and now most commonly they are plastic. The hook on the right side of both the levers below can go around a spoke to hold one lever in place while you use a second lever on a different section of tire. The left end is used on the tire bead.

The most important feature of a tire lever is that it does not have any sharp edges that may "pinch" the tube (that is, become wedged between the tube and the tire) causing a small hole or tear in the tube.
Operation of tire levers usually involves either a pair or a triple set of levers. Levers can also be used help get a tire onto a rim when it is a particularly tight fit.

Plastic & Alloy tire levers

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

  • Is it possible to use the metal irons with anodized rims without damaging the coating? I bought some cheap ones, and they're ribbed on the face, and a bit sharp on the edge of the face, and when they slip, they dig in to the rim a bit.
    – naught101
    Commented Sep 28, 2013 at 0:04
  • and a question here: bicycles.stackexchange.com/questions/17743/…
    – Móż
    Commented Sep 28, 2013 at 5:01
  • 1
    IIRC, the plastic ones were (decades ago) also called "milk levers" because the original plastic ones were made out of recycled plastic milk containers (or so the story went).
    – FreeMan
    Commented Feb 22, 2023 at 17:27


Attaches the handlebars to the bike, or, more precisely, to the steerer tube. Stems are designed differently for different headset types (i.e. threaded or threadless). They are also sized to suit different diameter handlebars and in the case of threadless setups, different diameter steerer tubes.

Stems play a key role in setting your riding position. You can adjust the reach to the handlebars by changing the stem's length. Separately, you can move the stem vertically to change your riding position. Stems for road bikes typically come in lengths ranging from 80 to 140mm. Mountain bikes have moved to significantly shorter stems than this. If you need a stem much shorter than 80mm on a road bike, that is a sign the bike doesn't fit you. All else equal, a shorter stem will make for quicker handling. If you are buying a new bike and you know you need a different stem length, the bike store should be willing to trade your stem for something they have in stock.

Another characteristic of stems is their angle. Threadless stems commonly come in angles around -10 degrees, sometimes more. You can flip a threadless stem so that it increases the height of the bar. There are also angle-adjustable stems made, so the rider may change bar positions without removing the handlebars or changing the stem, although their length typically can't be adjusted. An adjustable stem is shown below.

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

The picture below shows several threadless stems of various lengths. All have spacers under the stem. New bikes come with the steerer tube uncut and a number of spacers, up to 40mm (or more), made in 5mm or 10mm increments. It is common to cut off the excess steerer tube above the stem after you finalize your position. However, you can leave some spacers above the stem, as in the top right picture. In fact, it is advisable to, in case your position changes or you sell the bike.


The picture below shows some threaded stems (also called quill stems). They are shaped like a number 7. The expanding wedge on the bottom of the stem secures the stem inside the steerer tube, and it is activated by the binder bolt on the top of the stem. The stem threads into the steerer tube. Threaded stems have some inherent vertical adjustment available, although be cautious of the maximum and minimum insertion marks.

It is common for threaded stems not to have a removable faceplate, whereas this is rare for threadless stems.


This folding bike effectively has a stem of nearly zero length.


  • 2
    Not to be confused with a valve stem.
    – hobbs
    Commented Jun 29, 2022 at 19:02
  • This might need a section on Stem Cap and Stem Spacers - too small for their own section but are absolutely related to stems.
    – Criggie
    Commented May 27, 2023 at 2:11

Dunlop Valve

aka Woods valve or English valve

The Dunlop valve is an older style valve that is no longer commonly found in the english speaking world. It is still commonly found in Japan, Germany, and the Netherlands on non-speciality bicycles. The advantage of a Dunlop valve is that it is very easy to manufacture. The main pressure control mechanism is a simple rubber tube called a "plug" or "worm" that can be easily replaced. However, the rubber plugs also quickly degrade and this can be a cause of frustration for users. Recent Dunlop valves in Japan come with mechanical springs rather than plugs.

A pump designed for a Presta valve can be used to fill a tube with a Dunlop valve.

Modern versions of this valve use a different method to keep the air in, a small ball in the valve and a rubber ring that does not stop the air flowing in. These hardly ever fail in use but can get stuck if not pumped in a long time.

Dunlop Valve

More information: Dunlop valve (Wikipedia).

Go to Presta valve.
Go to Schrader valve.

Also see this answer.

  • 6
    This is the most common valve on everyday usage bicycles in The Netherlands Commented Oct 19, 2010 at 7:40
  • 1
    and possibly here in Poland too
    – Marcos
    Commented Mar 8, 2012 at 18:22
  • 2
    And Japan, almost all non specialty bikes are Dunlop valves.
    – RoboKaren
    Commented Jul 15, 2015 at 15:19
  • Very common also in Germany. We distinguish the interior: rubber plug vs. "Blitzventil" (flash valve): Rubber plugs are notoriously hard to pump because there's a lot of pressure lost at the plug, the Blitzventil has a ball valve which works basically without any pressure loss.
    – cbeleites
    Commented Jul 22, 2019 at 10:19

Derailleur hanger

Rear derailleurs bolt to a hangar beside the right rear dropout. As in the pictures below, most derailleur hangers are separate pieces of metal, usually aluminum, that bolt onto the dropout. These are called replaceable derailleur hangers.

Replaceable derailleur hanger derailleur hanger 2

Derailleur hangers frequently bend slightly if a bike is dropped or crashes, which is especially common off road. This can compromise shifting. However, the advantage for replaceable hangars is that they bend and break before the derailleur or the frame. The hanger can then be bent back or replaced. Replaceable hangers are proprietary to each frame and tend not to be interchangeable. However, manufacturers will usually stock them as replacement parts, and your bike store should be able to determine which one to order. If the manufacturer can't be contacted, there are third party manufacturers and sellers of these hangars.

The picture below, from Park Tools, shows a bent hangar. Notice how the rear derailleur's cage is at an angle to the cogs. You can usually notice a bent hangar visually. In less obvious cases, bike stores have specialized tools to measure if a hangar is bent and to bend it back.

enter image description here

Non-replaceable derailleur hangers are part of the dropout, as in the picture below. (Note that this bike is set up and singlespeed, with a derailleur in place you would never put the axle this far forward in the dropout)

derailleur hanger integrated in the frame

Some steel and titanium bikes have non-replaceable hangars. If these are bent, they will need to be cold set (i.e. bent) back into alignment, although titanium hangars can be difficult to bend. If a non-replaceable derailleur hanger breaks, an experienced welder (preferably a frame builder) will need to replace it.

  • why is a separate hanger safer?
    – naught101
    Commented May 12, 2012 at 3:01
  • @naught101 because if it bends/breaks you can substitute it. it is actually a breakable part, softer than the frame, so that any force will act on this piece instead of the frame.
    – bigstones
    Commented May 12, 2012 at 11:02
  • So it's more about safety for the bike than for the rider?
    – naught101
    Commented May 12, 2012 at 12:19
  • @naught101 yes. I'm not an english speaker, so feel free to reformulate that part.
    – bigstones
    Commented May 12, 2012 at 13:32
  • 4
    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
    Commented Mar 17, 2014 at 7:02

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 when new and clean.

enter image description here

Fingers are usually too weak for the worn chain, and another specialized tool, chain pliers (image credit), is then used to disconnect or connect the master link:

enter image description here



A bearing is an interface that enables the axle to rotate inside some fixed part. The axle rolls on the bearings. For example, consider your hubs, pedals, the cranks, and your front fork. Sheldon Brown has a longer discussion on bearings. Most bearings are steel balls.

Preload is important term related to bearings. For your hubs, preload is how much the hub is getting squeezed in from the side, ignoring the quick release skewer. All cup and cone hubs have inherent preload adjustment, but not all cartridge bearing hubs or other devices do. Too much preload will make the bearings grind and wear out. Too little preload can leave play in the hub (i.e. side to side movement when the quick release skewer is clamped) or other device (e.g. crankset, headset will rock back and forth).

Bearings will feel gritty when they are worn or dirty. You can feel this by spinning the wheel in your hand, holding near the axles, or otherwise working the component by hand. In some cases, e.g. you submerged the bike during a river crossing, you can wash out the grease from the bearing, and cause it to sound dry (a whirring sound) but not feel gritty. If the bearing feels notchy or indexed, this can mean too much preload, or that the bearing bore is not round (e.g. it's been ovalized).

Cup and cone bearings

Wheel bearing -- from Park Tool site

This type of bearing, pictured above, has the balls rotating between the cup and the cone. The locknut tightens the assembly together, and can be loosened with a standard sized wrench.

Cup and cone bearings require periodic service. Service involves cleaning out the old grease, which may have had some dirt mixed in with it, and adding fresh grease. If the balls are worn, you can measure their size with a caliper and buy replacements. Alternatively, manufacturers' technical documentation will frequently state the size and number of ball bearings; take note that sizes for front and rear hubs may be different. Eventually, the cones should wear, and manufacturers should maintain these as replacement parts as well. The cups may not be replaceable, as they are frequently integrated into the hub or pressed in extremely tightly.

Cup and cone bearings are more traditional and are frequently present on older equipment, but some companies persist in making high-quality cup and cone bearings (notably Shimano and Campagnolo).

Cup and cone hubs all require preload adjustment. Best practice is to tighten the locknuts so that there is barely perceptible play when the hub is off the bike, and zero play when the quick release or thru axle is tightened. Some cartridge bearing hubs require preload adjustment.

Cartridge bearings

Most manufacturers have moved to cartridge bearings. In many contexts, cartridges are sealed units that can contain things like printer ink, film, or, in bicycles, ball bearings, seals, and races (roughly equivalent to the cone and the cup respectively). Sometimes they are called sealed cartridge bearings, and most of the bearings in bicycles have rubber seals, but this is potentially a misnomer. Bicycle bearings might be unshielded at one end, and cup and cone bearings can have seals built in.

enter image description here

To replace cartridge bearings, you will need a bearing extractor to pull or push the bearing out, and a bearing press to push it back in. Related to presses, bearing drifts help align the bearings as they are going in. Bike stores frequently have these items. As a makeshift replacement for a bearing press, you can use a block of wood and a hammer, but you need to visually confirm the bearing is going in straight. For bearing extraction, you can use a screwdriver or chisel and a hammer, and carefully hammer the bearing out. Both procedures may damage the bearing seat, however.

The bearings themselves are available commercially from many suppliers. A competent mechanic will know how to measure the bearing size. However, measuring the outer diameter, inner diameter, and depth are often sufficient to give you a bearing size. Bearings are commonly sold by coded numbers, which correspond to size. For example 6806 bearings are common in rear hubs. They have a 42mm outer diameter, 30mm inner diameter, and are 7mm deep.

Bearings are sealed to keep contaminants out. Contaminants would wear the balls or races out. Most bicycle bearings have rubber seals on both sides, but other arrangements exist. If uncertain, check with a mechanic.

Most cartridge bearings are designed not to be serviced. Just replace them when worn. Some higher-end manufacturers (e.g. Chris King, Kogel) design their bearings to be serviced periodically. This entails gently removing the rubber seals, cleaning the grease, and adding fresh grease. If there are no specific instructions, assume that there is no need to service the bearing.


Many factors may influence the durability of the bearing. If you ride in wet conditions, this will reduce durability. If you pressure wash your bike, take care not to point the hose straight at the bearings (in your hubs, bottom bracket, rear suspension pivot). As stated earlier, some bearings are more tightly sealed than others, trading off higher friction.

In a press fit bottom bracket, if the bottom bracket seats are not parallel to each other or if one is out of round, that can damage the BB over time. Bearings also have a load capacity. If a piece of equipment was designed with bearings that are too small to take the loads applied to it, that would also impact bearing life. Additionally, all else equal, the more narrowly spaced the bearings are, the higher the loads on them will be. This does affect some press fit standards, like BB30 and PF30, which have their bearings more narrowly spaced than others. Last, the material quality of bearings and the races they run on has an impact. This would include the specific steel alloys used as well as their pureness, and how smooth they are.


Ceramic bearings are sometimes offered as an upgrade on high-end bikes. They have marginally lower rolling resistance than high-quality steel ball bearings. In many industrial applications, ceramic bearings are thought to be more durable, but this may or may not transfer to bicycling applications. In addition, ceramic bearings are extremely hard, and they must be paired with a high-quality steel race, or else they can dent the race when the bike goes over bumps. Many cheap ceramic bearings may skimp on the quality of the races, and buyers should beware.

Bushings (link to Wikipedia) are another form of bearing. These involve a sleeve rotating over the axle. Bushings are often used in rear derailer jockey wheels and in mountain bike suspension.

  • Anyone who has the knowledge, please feel free to expand on this. Commented Feb 9, 2011 at 4:39


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 which thread onto a threaded portion of the steerer tube.

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 or steerer tube 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 steerer tube.

Threadless Headset

Images courtesy of Sheldon Brown.


Chain Tug

AKA: Chain Tensioner

On most bikes, the rear derailleur keeps the chain in tension. On fixed gear, single speed, or hub geared bikes, a chain tensioner is required to keep the chain in tension. Without this mechanism, the chain may fall off, or the rear wheel may pull 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

  • Small correction: A chain tug is only used and required with those horizontal, rear-facing drop outs. And that is not popular everywhere. In other countries, single speed and IGH bikes use forward facing dropouts where the axle is held in place by friction (requires proper tightening of the axle nuts). This makes it extremely easy to take out the rear wheel, or to replace it (no need to open the chain lock, you can simply pick the chain off the sprocket after taking out the wheel), and is surprisingly robust if tightened properly. Commented Nov 11, 2021 at 8:02

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. It does allow for different size wheels as well as the gears, but it ignores the effect of different crank lengths.

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
GI     = Gear Inches
CrT    = Chain Ring Teeth
CogT   = Cog Teeth
D      = Wheel and Tire Diameter

For example, a 700c tire is going to have a diameter of roughly 26.3" (depending on the width of the tire). Note that larger tires on the same wheel will give higher gearing (i.e. more gear inches), even though the gearing (i.e. chainring and cog) are the same. 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.


Chain gauge

Measures the stretch of a chain to determine how worn it is and when to replace it.
It's made to fit exactly between two separated links of a standard chain. Synonyms include: chain wear gauge, chain checker chain guage

Alternately you can measure the chain with a ruler - standard links are 1inch (25.4mm) long.

Note - the chain doesn't actually stretch, the pins connecting the links wear away making the joints looser. The extra movement reduces efficiency, causes the chain to skip and will wear the rear gear teeth.

  • Note that tools that work this way are not especially accurate, to work properly both measurement points should be on the same side of the pin they're measuring.
    – Móż
    Commented Jun 10, 2014 at 2:35

Bottom Bracket (BB)

The cranks attach to the bottom bracket (BB), which contains bearings that let the axle rotate. BBs may incorporate the axle the axle that the cranks attach to, or the axle may be bonded to the cranks and pass through the BB. The bottom bracket shell is the part of the frame holding the bottom bracket. Road and mountain bikes have different BB shell widths, so you can't interchange their cranksets.

Threaded bottom brackets

Traditional bottom brackets screw into the bottom bracket shell. Many frames with threaded BBs use a standard called the Birmingham Small Arms (BSA) standard, also called English, British, or ISO. Italian bikes are more likely to use Italian threading. There are a few older standards, which Sheldon Brown describes. To replace a threaded bottom bracket, you will need to know your frame’s shell type.

For a time, Shimano and others built on this style of BB with oversized hollow spindles. These were stiffer and lighter, but the spindle left less room for bearings and the BBs may have been less durable as a result.

External bottom bracket cups came into play in the mid 2000s. Here, the bottom bracket assembly contains only the bearings, and the crank axle is attached to one or both crankarms. The axle goes through the bottom bracket.

Press-fit bottom brackets

Later, various press-fit bottom bracket standards were developed for carbon fiber bikes. It is not possible to cut threads into carbon fiber, and press fit systems are a bit lighter. The alternative was to bond an aluminum threaded sleeve in. However, press fit has a reputation for creaking, in part due to inability to maintain tight tolerances during carbon manufacture.

There are numerous press fit standards. Cups for one standard are not interchangeable with a different standard. However, for each press fit BB standard, manufacturers will make cups to accept most or all cranksets on the market. Examples of open standards include BB86 and Press Fit 30. Some larger bike manufacturers have BB standards proprietary to their own frames, such as Cervelo (BBRight), Cannondale (BB30 and descendants), and Trek (BB90, although they appear to be transitioning to the open, threaded T47 standard as of 2021).


Most BBs use cartridge bearings. The whole BB is replaced when the bearings are worn, as discussed in the article on bearings. Some BBs with cartridge bearings may be serviceable, which usually involves removing the seals, using a degreaser or WD40 to clean the bearings, and then regreasing, but most of the time the bearings themselves aren't physically accessible. Riders should avoid spraying water directly at the BB from the side of the bike when cleaning it.

Selecting a Bottom Bracket

For square taper systems, you need to know the length of the taper (e.g. 108mm) and the type (JIS or ISO). A bike store can help you measure the length if you don’t know it. For modern cranks, you need to know both the BB shell type (e.g. BSA, PF30) and axle type (e.g. Shimano, SRAM DUB, Campagnolo, other). For example, a BB described as PF30-24 or similar wording fits a PF30 shell, and it can only take a 24mm spindle (i.e. Shimano, although some third-party cranks make compatible spindles). PF30-DUB would fit a PF30 shell with a SRAM DUB (28.99mm) axle. Confusingly, if a BB were to be described just as PF30 with no other suffix, you can assume it fits a PF30 shell and a 30mm axle.

Most but not all crank spindles can mount to most BB shell types. Manufacturers even make BBs for 30mm spindles in BSA and Italian shells, even though a 30mm spindle is a tight fit in those shells. One clear exception is that Trek's proprietary BB90 standard is incompatible with many 30mm spindles. There may be a few more cases of incompatible hardware.

Last, if you have a BBs designed for larger spindles and you wish to fit a crank with a smaller spindle, this may be possible through adapters. For example, 30mm to 24mm spindle adaptors exist, and SRAM's older GXP spindle (22mm on the non-drive side, 24mm elsewhere) fits in a Shimano-compatible BB with one adapter. In general, arrangements with adapters are more likely to creak than using the correct equipment. This is because the combined system has greater variances in dimension. Also, not all systems can be adapted.

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.

Miscellaneous terms and concepts

  • The right (drive-side) cup on BSA BBs is left-hand threaded, i.e. you tighten it counter-clockwise. This may be counterintuitive, but if the thread directions were reversed, pedaling would tend to unscrew the cups. Italian BBs are right-hand threaded on both sides, and their drive-side cup sometimes comes out unless fixed with adhesive, e.g. Loctite.
  • If a BB shell's threads are damaged, e.g. by cross-threading (screwing something in at an angle), they can be chased by a tap to restore them. This can also be called reaming.
  • Metal bottom bracket shells should ideally be faced before frame assembly. Facing means making sure the lips of the BB shell are exactly parallel to each other, shaving down any excess metal or carbon. In the photograph below, the BB shell has not been faced properly. The cup is at a slight angle, as you can see by the small gap towards the top of the photo. This can lead to creaking or to shortened bearing life. Press fit shells and disc brake mounts, including on carbon bikes, can also benefit from facing.

enter image description here

  • 1
    Note: may be at the front or back of the bike rather than the bottom. And is not a bracket.
    – Мסž
    Commented Apr 20, 2011 at 4:38
  • I've recently been made aware of sealed, unsealed, and external BBs. Can here anyone expand on the difference between them? Commented Jul 31, 2011 at 16:00
  • This actually describes the bottom bracket shell. The bottom bracket is the bearing assembly and is usually removable...
    – freiheit
    Commented Oct 31, 2012 at 17:25
  • @freiheit - fixed, feel free to edit further. Commented Nov 1, 2012 at 19:52
  • Ok, I edited the heck out of it. I didn't mention sealed/unsealed, but I did explain external BBs and tried to explain the new external-style-but-actually-go-inside-a-larger-shell-BB style that I can't figure out the standard name for (it's called "press-fit" on one of my bikes, but the same thing also can screw in...)
    – freiheit
    Commented Nov 2, 2012 at 23:34


A groupset or gruppo (from the Italian for "group") refers to the components involved in shifting gears, braking, and transmitting power from the rider's legs to the rear wheel. Relatedly, sometimes people say "drivetrain." In bicycles, the term is not formally defined, but it definitely includes the chain, chainrings, and cassette.

Groupsets typically include:

  • integrated brake levers/shifters (on older bikes, brake levers and down-tube or bar-end shifters)
  • front and rear brakes (including calipers/pads or rotors/disks/pads)
  • rear derailleur
  • front derailleur (unless the bike has a 1x drivetrain)
  • bottom bracket
  • crankset or chainset
  • chain
  • cassette (freewheel on older bikes)
  • cables and housings or hydraulic hoses as appropriate (for electronic groupsets, control wires and batteries)

In the past, groupsets have included some or all of the following components or groupset manufacturers have offered these items, but these are not considered parts of the groupset.

  • headset
  • hubs and usually quick release skewers
  • stem and seatpost may have been included, or may have been optional purchases
  • pedals are typically optional purchases

SRAM Red Groupset

Shimano, SRAM, and Campagnolo account for the vast majority of road bike groupsets. SRAM had entered the road bike market in 1988, then exited, then re-entered in 2004. Shimano and SRAM are the majority of the mountain bike groupset market. Campagnolo briefly produced one mountain bike groupset before exiting that market. At the time of writing, Full Speed Ahead and Rotor have produced groupsets as well, but these have yet to achieve widespread take up.

Groupsets are offered at a range of price points. Each of the 3 major manufacturers makes one version for professional road (e.g. Campagnolo Super Record) or mountain bike racing (e.g. SRAM XX1). They also offer various lower level groupsets for consumers. Generally, the high-performance consumer groupsets (e.g. Shimano 105 and Ultegra) will have less exotic material (i.e. less titanium and carbon fiber) used in manufacture and will be heavier, but will usually offer very similar performance on other characteristics (e.g. durability, shift quality). Groupset manufacturers generally offer electronic shifting versions of their top two groupsets.

The original equipment manufacturer (OEM) market is dominated by Shimano and SRAM (i.e. most complete bicycles come with Shimano or SRAM components). For the most part, shifters and derailleurs are not compatible between brands, and complete bicycles will not mix these components. However, some complete bicycles will substitute cranksets and/or brakes from third party manufacturers for cost or performance reasons.

  • 1
    Is "drivetrain" a synonym of "groupset?" I've heard the two words used almost interchangeably in many contexts.
    – Jules
    Commented Sep 23, 2015 at 16:02
  • @Jules In motorized vehicles, drivetrain is the set of components that deliver power from the engine to the wheels (excludes the motor). On bikes, I believe that people usually mean the crank, chain, and rear derailleur. It may include the cassette. In principle, the pedals connect the cranks to your legs, so maybe they should be included. I don't think this would fit with common usage (but I could be wrong).
    – Weiwen Ng
    Commented Sep 25, 2019 at 20:46

Fender (US usage)

Mudguard (UK usage)


A must for winter or wet weather cycling. As the wheel rotates, it will spray water and dirt up a rider's back, onto various parts of the frame and drivetrain, and onto riders behind. Fenders block this spray. They are often recommended for riding in wet weather. They may even be required on some group rides, depending on climate.

Mudguards are flaps attached at the ends of a fender that reduce spray further. They are usually bought separately from the fender.

fender / mudguard

Commercial fenders can be made from metal or plastic. Fenders and/or mudguards can also be DIY'ed from plastic milk cartons. Full coverage fenders require the frame and fork to have fender mounts. However, some fenders, like the ones depicted, can attach on to the frame and fork directly. This mounting is less secure, and such fenders do not cover as much of the wheel.

If an object like a stick gets jammed between the tire and fender, it can cause the fender to break off. The frame may be damaged as well. If there is not much clearance between the fender and tire, this may be an argument for using fenders made for race bikes. These fenders may just bolt to the seat stay and down tube, and will offer partial protection from dirt and water.

Related: the fender stays are the rods that connect to dedicate mounts on the bike.

  • 5
    A link to a good DIY fender tutorial would be good here.
    – naught101
    Commented May 13, 2012 at 4:29
  • 3
    I'd suggest that a mudflap is different to a mudguard or fender. Mudflap is usually the wide, flexible extension which hangs on the rear end of the mudguard: sjscycles.co.uk/mudguards-mudflaps Commented Sep 27, 2016 at 21:15
  • 1
    It should be added that some road-riding clubs see mudguards as mandatory for wet and/or winter rides - the reason being that they stop the rider behind you getting a mouth full of whatever is currently on the road.
    – David Kemp
    Commented Oct 22, 2019 at 11:54

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.

  • Can you explain what you would use it for? I'm betting most people don't install their own brake cables. Commented Sep 6, 2010 at 17:53
  • 1
    I have never had problems installing brake cables with a standard set of pliers.
    – Ian
    Commented Sep 17, 2010 at 9:22
  • 3
    @neilfein, I tend to solder the ends of cables after I have cut them to stop any fraying.
    – Ian
    Commented Feb 9, 2011 at 11:37
  • 1
    @Ian superglue also works! Commented May 16, 2016 at 8:01
  • 1
    I'd know this as a third-hand tool. I have two hands, if this tool is the fourth hand.... who or what is the third hand ? the pinch bolt you're tightening ? LATER UPDATE - the "third hand" tool is one that holds the rim brake pads against the rim so you have your first two hands to manage the pinch bolt and tool.
    – Criggie
    Commented Feb 14, 2020 at 22:41

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). Longer chainstays stabilize the bike's handling. Touring and many gravel bikes have longer chainstays, whereas many racing bikes, especially on the track, have short ones.

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. Frames with horizontal or adjustable dropouts have variable chainstay length, unlike frames with vertical dropouts. In the former case, the manufacturer may state the chainstay length as measured to the middle of the adjustment range.

Chainstay Length

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



The part of the bike you hold with your hands. When you turn the handlebars, the front wheel turns with them. The stem clamps onto the handlebar and onto your fork steerer.

Broadly speaking, there are flat handlebars as found on mountain bikes and hybrid bikes, and drop handlebars which have bar ends that are curved below the flat portion. Flat handlebars offer better control in rough terrain. Drop handlebars are used on road and gravel bikes, and they offer a wide variety of hand positions. This question discusses in some detail the various positions you can take on drop bars.

If you are replacing handlebars, they are mainly characterized by their width. For drop bars, one guideline for road bikes is that the bars should approximately equal your shoulder width. Gravel cyclists frequently opt for relatively wide bars, and they also opt for flared bars where the drops are wider than the hoods. Professional road racers are increasingly opting for narrow bars. Mountain bike handlebars are significantly wider than road bars, and are frequently trimmed to the desired length after some experimentation.

This question discusses different subtypes of each of the two classes of handlebars.

Additional information:

Sheldon Brown on handlebars, drop bars, and upright bars.



One of the central parts of a conventional bicycle wheel. Hubs are flanged metal tubes, somewhat similar in shape to spools of thread. Hubs contains bearings and an axle, and they are connected to the rims via spokes. The rear hub holds the freewheel or cassette.


The bearings in your hubs are wear items. This is discussed more in the bearing article, but cup and cone hubs require annual service. The cones may eventually wear out and can be replaced. Cartridge bearings usually do not require service, but they will eventually wear out. A competent bike store or a consumer with the right tools can pull them and replace them. The freehub body can often be obtained from the hub manufacturer as a replacement if it wears out. If the hub is OEM equipment on a complete bicycle, the bike store should be able to search for replacements in their inventory.

Good hubs can outlast a rim. Currently, many consumers buy complete wheels, but you can also buy separate hubs and ask someone to build you a wheel, or have a hub from a damaged wheel taken out and reused. If you damage or wear out a rim, consider if rebuilding on the same hub is more cost-effective than buying a whole new wheel.

For consumers, some key features are:

  1. Spacing and axle type

If you are getting a new wheel, you will need to make sure that these features match your current bike. Quick release road and MTB hubs had 130 and 135mm over-locknut diameter respectively. On thru axle hubs, road hubs wheels use a consistent spacing and mostly use 12mm diameter thru axles front and rear. MTB hubs likely use 15mm diameter thru axles, but you need to consider if the bike uses Boost spacing (148mm in the rear) or not (142mm, same as disc road bikes).

  1. Drivetrain

You need to match the rear hub's freehub body to your drivetrain. Shimano road hubs have mainly used the Hyperglide system, but the 12s Dura Ace hubs are transitioning to a different spline system (name not yet determined), and they use the Microspline system for MTBs. SRAM has shifted to the XD and XDR driver systems. Campagnolo has maintained its own freehub spline pattern, with an additional variant (called N3W) to accommodate the small cogs on its Ekar gravel groupset. Alternatively, you may have a freewheel hub, and you would thread a freewheel onto the hub.

If you switch drivetrains, replacement freehub bodies are usually available from the hub manufacturer.

  1. Disc or rim brake

Hubs designed for disc brakes will have their flanges spaced so as to accommodate the rotor, and they will have a mounting system. As to the latter, the two rotor mount standards are 6-bolt (mostly used on MTBs) and centerlock (used on drop bar bikes). Rim brake hubs cannot be used in disc brake systems, as there is nowhere to mount the rotor.

  1. Other features
  • 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. They may use belt drives or chains for the transmission.
  • Track/fixed-gear hubs may have narrower spacing than other hubs. They will not have a cassette body, and they will accept a thread-on cog on one side of the hub.
  • Flip-flop hubs have 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 not be strictly true, but Campagnolo was one of the first to put a high-quality quick release skewer into serial production.
  • 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 (i.e. a mid drive e-bike).
  • What is the actual name of the cylinder on which cassette goes? Wikipedia states "splined shaft", here you use term just "splines". Commented Mar 26, 2019 at 18:31

Track pump or floor pump

A large pump that you use by standing on the bottom plate and moving the handle up and down. Despite the name, these are not limited to track bikes. 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
  • Optional: a secondary air chamber to seat tubeless tires

Manufacturers may sell spare parts for pumps that break. If your pump is leaking air or not inflating, it’s possible that you may just need to change a rubber o-ring inside the pump. Replacement gauges are another common item.

  • Also useful for Dunlop valves (which are very much still used by bicycle users in some countries.)
    – Willeke
    Commented Nov 21, 2021 at 15:44

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