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

Question

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

Some Rules

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

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

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

A road bike has the following parts (source):

A mountain bike has the following parts (source):

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

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Contents
A Actuation Ratio Axle	Axle Nuts
B BCD (Bolt Circle Diameter) Bearing Belt Drive Bidon/Bottle Bonk/Bonking Bottle Cage / Bottle Holder	Bottom Bracket Boom/Boom Tube Brazed Frame Brifter BSD (Bead Seat Diameter) BSO/Bike-Shaped-Object
C Cable Pull Cable Stretcher Cadence Cassette Chain Chainline Chain Gauge Chain Guard/Cover	Chain Tool Chain Tug/Chain Tensioner Chainstay Length Chainsuck Chamois Clipless Pedals Coaster Brake (foot brake / pedal brake) Crank
D Derailleur Derailer Hanger/Derailleur Ranger DetanglerBMX Direct Drive Disk/Disc Brake Disc Hub	Door Zone Dropout Dropper Post Dunlop Valve Dutch Bike
E Engine/Motor	Electronic shifting Eccentric
F Fender/Mudguard/Mudflaps Fixed-Gear Flip-Flop Hub Folding Bike Fork	Foot Peg Frame Frame Sizing
G Gear Inches	Groupset
H Handlebars Headset Hose Clamp aka Jubilee Clip	Hub Hub Skewer
I Internally-Geared Hub
J
K Keel Tube
L Lawyer lips/lawyer tabs Lateral Tube LBS/Local Bike Shop	Lights Luggage Carrier/Rack Lugged Frame
M Master Link MIPS	Mixte Mountain Bike
N Noodle
O Over Locknut Dimension or OLD
P Pannier P-clip or R-clip Play Potts Mod BMX Brakes	Power Meter Presta Valve/Presta Tube Pump Peg
Q Q-Factor	Quick-Release
R Recumbent Cycles REI (Recreational Equipment Inc) Rim	Rim Tape Rim Brakes, e.g. cantilever, dual pivot, V-brakes Rotor
S Saddle Saddlebag Schrader Valve/ Schrader Tube Shaft Drive Single-speed Skewer	Spider Spoke Stack and Reach Stay, Mudguard/fender Stem Suspension Fork/Rear Shock
T 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 Tolerances Track Pump/Floor Pump Triathalon Bars/Triathlon Bars
U U-Brake
V V-Brake Velomobile
W Welded Frame
X
Y
Z

Answer 1

Potts Mod

This is a brake cable layout design done primarily on BMX bikes, combined with a Detangler that allows the front wheel and handlebars to spin 360 degrees without getting stopped by wires and cables.

This dates from the 80s, and was originally done by Steve Potts, hence the name.

Since BMXs are mostly singlespeed, there are no gear cables involved.

Instead, the front brake cable outer runs down through the hollow steerer tube of the fork and therefore through the headset bearings.

White outer cable passing through a hole in the top of a BMX stem. Look closely and you can see the hole is through the middle of the stem bolt, which has an external hex drive instead of an internal one, and so has to be exposed and not recessed. The quill stem bold goes down inside the steerer tube and the access hole goes right through, so the bolt needs to be sufficiently strong despite being hollow.

Same outer cable drops out the bottom of the fork crown, just above the tyre, and is well-secured to one fork-leg.

Lastly, the cable loops back up to the front brake. Yes, this cable is excessively long and risks catching on things, but I intend on redoing it with black outer which is harder to photograph.

You would generally find this done with U brakes as pictured, or traditional caliper brakes rearranged to have the cable enter from below, not above.

A race BMX would not need this - instead it would be a Freestyle or Trick BMX used for stunts or performances. This bike is also equipped with Foot-Pegs and a Detangler

Note these photos show a Diamondback BMX that has these features built into the design from new. This change was originally a literal modification, and was the only change needed to allow for barspins, when the bikes have a coaster/backpedal brake.

Downside: The downward loop of outer cable holds moisture and will rust out faster than normal. Ideally your brake cable would have an exit at the lowest point and could not hold water for long periods.

Links: https://bmxmuseum.com/forums/viewtopic.php?id=56527

Answer 2

Detangler / Rotor / Spinner / Gyro

Closely connected to the Potts Mod this is a brake setup that allows a BMX's handlebars to rotate 360 degrees without wrapping the rear brake cable around the headset of the bike.

Almost completely exclusive to Trick BMXs, this is not something that would be on a racing BMX.

The rear brake lever is conventional, but the cabling passes through a splitter. This gives two brake internal cables which are linked to the detangler.

The detangler is two separate metal rings with tabs, secured together with a thin ball bearing that goes around the stem/headset. As the bars turn, the bearing operates, letting the top metal ring stay in line with the bars, while the bottom ring stays with the bike.

When the rider pulls the rear brake lever, both sides of the detangler lift, which pulls the next two wires. This avoids the detangler from going off-horizontal and binding which would stop the brake from working.

Not pictured is a down-stream splitter in reverse, that recombines both wires and has a single cable coming out to actuate the rear brake.

Downsides, this system adds weight, and also introduces flex so the rear brake is less snappy. There are three more metal parts which could tap on the frame making noise. The bearing is relatively poorly-protected too.

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Note: This is nothing to do with a disk brake Rotor, which is defined elsewhere.

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After writing this, I disassembled the brake planning to replace ~6 brake cables and many segments of outer and ferrules. Surprisingly, the cable set is not standard with the splitter/combiner acting to clamp normal inners; instead the top and bottom Y shapes are one unit each.

As you can see the two wires really are permanently secured to the single wire. So a replacement rear brake cable set for a BMX with a detangler is a specialist item.

Answer 3

Over Locknut Dimension, abbreviated O.L.D. or OLD.

O.L.D. refers not to the length (width in the image) of the axle, but to the distance between the outer surface of the two locknuts.

Due to the lack of standardization for cups and cones, replacing just a cone is difficult. It is considerably easier to match the Over Locknut Dimensions (O.L.D.) and the diameter of the axle. If these two dimensions are matched, then any cone with curvature vaguely resembling the old cone will likely be fine.

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Similarly, the Over Locknut Dimension has to match the frame into which the wheel will be installed.

from https://www.sheldonbrown.com/frame-spacing.html, showing a 126mm OLD frame.

OLD of a frame can be tweaked under some circumstances, but not by much and the frame has to be steel. 126mm to 130 would be fine, and 130 to 135, but 126 up to 135 would be stressing the frame too much. You might need to re-align the dropouts afterward. Never do this with aluminium or carbon frames.

OLD of a wheel can often be adjusted by adding/removing spacers, and swapping spacers from side to side.

Common OLD measurements may be found at https://www.sheldonbrown.com/frame-spacing.html

Answer 4

Chainline

Chainline is the relationship of the sprockets to the centerline of the bike.

Front Chainline

On a 1x system, the front chainline is the perpendicular distance from the chainring to the center plane of the bicycle.

On a 2x system, measure the distance from the middle of the two chainrings.

On a 3x system, measure from the center chainring.

Rear Chainline

The rear chainline is the perpendicular distance from the middle sprocket (among an odd number of sprockets) to the center plane of the bicycle. For even sprockets use half the distance between the middle two sprockets.

Answer 5

Dutch Bike

Synonymous with: utility bicycle, city bicycle, urban bicycle, European city bike (ECB), classic bike or simply city-bike

Dutch bikes are designed for every day use in rain and shine, for short-distance commuting, running errands, shopping, leisure and known for their often minimal features, rugged reliability and upright riding position.

Classic design features are:

• features to keep the riders (regular) clothes clean of mud/oil/snow/dirt and prevent them from catching on the chain or in the spokes:

  • fully enclosed enclosed chain guard
  • skirt/coat guards
  • front and rear fenders/mudguards

• clean and rugged design:
  No features that are easily damaged in crowded bike parks,
  and omit features that require regular maintenance:

  • no external brake cables and/or brake levers on the handlebar but instead:

    coaster brakes

  • no derailleur, external shift cables and shifters but rather:

    single speed

  • fully enclosed enclosed chain guard to keep the chain clean and protected from weather and dirt.

• front and/or rear luggage carrier

• fixed front and rear lights powered by a dynamo

• Single, dual or adjustable kickstand

• O-lock

• curved and (slightly) elevated handlebar facilitating the upright riding position.

Common standard improvements and upgrades are:

• Improved brakes, i.e. disc or rim brakes instead of or in addition to the coaster brakes

• Additional gears, typically with an internally geared hub to keep it low maintenance

• hub dynamo rather than a rim dynamo

• belt drive rather than chain (relatively expensive and still not too common)

In comparison a commuter bike is designed for longer rides and typically offers more gears, associated more powerful brakes, suspension and a less upright and more active and dynamic riding position.

Answer 6

R-clip or P-clip

These are the clips that attach the fender stays to the frame. Both metal and plastic clips are used.

These should clamp down firmly on the stay because they are providing structural support. Rubber-lined ones are more intended for supporting wires loosely, which is wrong here.

Stays come in different thicknesses; check yours before buying. Use threadlocker on the bolts too.

Answer 7

Tolerances

Every manufacturing process has variance. That is, for each dimension specified (e.g. diameter of a bore, length of a part, how round a bearing seat is, how parallel two bearing seats are), parts will vary slightly around the nominal (what that dimension is supposed to be). In engineering and manufacturing, tolerance (link to Wikipedia) is the amount by which dimensions are allowed to vary and still qualify as acceptable. That is, official specifications will show a dimension and a tolerance.

In common speech, people say a manufacturer has “poor tolerances” when they mean that a company has high variances in whatever important dimension. Poor manufacturing tolerances can cause play in components. As one example, cheap hex keys frequently fit sloppily in bolts because they may be a bit undersized.

As an example of tolerances in official specifications, the picture below is one manufacturer’s (FSA) specification for a BB386 EVO shell. The shell must be 86.50mm wide, with a symmetrical tolerance of 0.25mm. Note that tolerances can be asymmetric, as is the tolerance for the width of the bearing seats (46.00mm, +0mm, -0.050mm). Here, it's because having the bottom bracket press fit be a little tighter than expected is okay, but it would be bad if the press fit is too loose or entirely nonexistent. Some manufacturers may run poorer tolerances than others, i.e. their parts have higher variance in their important dimensions. Manufacturers presumably try to catch parts that are out of tolerance, but especially in high volume production, they cannot test every single part (they likely test batches for items out of tolerance, and they may reject a whole batch and investigate if enough items were found. There is an entire field of statistics behind this).

A side note: Tolerances/variances stack

In general, bottom brackets creak if they fit loosely in the frame. Tubeless tires may blow off the rim if they fit too loosely. "Too loosely" involves the tolerances of both the bottom bracket shell and the BB cup, or the rim and tire. That is, a brand of rim may work with many tires, but if you have a rim that's relatively small combined with a tire that's relatively large, you can have a loosely fitting tire.

Formally, the variance of the sum of two random variables (e.g. the mean diameter of a BB shell and the mean diameter of a BB cup) is the sum of their individual variances. Thus, the system has greater variance than a single component. (NB: technically, one also has to add 2* the covariance (similar to correlation) of the two quantities, but in the above scenarios the covariance can be assumed to be 0.)

Answer 8

Actuation Ratio

When a mechanical gear shifter is moved by the rider's hand, it will pull a predetermined length of inner Bowden cable through the outer housing. The derailleur at the other end will move (actuate) a different distance, which is determined by the actuation ratio.

Naturally there are many standards, along with exceptions to standards. In brief:

Shimano 6/7/8/9 - Rear shift ratio is 1.7, so for 1 mm of cable, the Rear Derailleur (RD) moves left/right by 1.7 mm
Shimano calls this 2:1 ratio for marketing reasons.

All these RDs are compatible, and any 6 to 9 speed RD will work perfectly with a 6, 7, 8 or 9 speed shifter (assuming the RD can physically span the width of the cassette). This is true regardless of whether the shifter and RD are intended for MTB or road. 6 to 9 speed RDs are also compatible with Shimano 10 speed road shifters (except the Tiagra 4700 series, which borrows the 11 speed actuation ratio.)

Name	Ratio
Shimano standard 6/7/8/9 speed and 10 speed Road excluding Tiagra	1.7x
Shimano Dura Ace 6 to 8 speeds (vintage stuff)	1.9x
SRAM 2:1	1.7x
Campagnolo old	1.4x
Shimano 10 MTB	1.2x
SRAM 1:1	1.1x
Campagnolo new	1.5x
Shimano 11 road and Tiagra 10 speed 4700	1.4x
SRAM Exact Actuation	1.3x
Shimano 11 MTB	1.1x
SRAM X-Actuation 11-speeds	1.12x
SRAM X-Actuation 12-speeds	1.01x

Note that Shimano Internally Geared Hubs (Nexus and Alfine) do not have equal pull distances, so adjacent clicks are NOT the same length. These shifters are incompatible with derailleur gears, and the IGHs do NOT work with normal shifters.

Further info:

• Are rear derailleur cable intervals equal?
• https://bike.bikegremlin.com/1278/bicycle-rear-derailleur-compatibility/

Answer 9

Velomobiles

A special class of recumbent cycles is fully faired, mostly three wheeled (although there are four wheeled versions as well) called Velomobiles, although many people may know them by different names.

The main advantage of a velomobile is higher speed for the same effort, but it comes at the price of being lower and therefor less visible on the road, paying more for the machine and often a bigger turning cicle.

My own Velomobile, a Quest, here parked in Beverwijk, the Netherlands.

There are also two wheeled fully faired cycles, but as far as I know those are not classed as velomobiles, they are the fastest that is out in man powered vehicles, whether single rider or a team of riders. This is a link to a magazine like internet page, a few years old, of an event which gets the fastest cycles.

Answer 10

MIPS helmet

A helmet with a low friction layer that allows the helmet to slide relative to the head following an angled impact. This is thought to reduce the rotational motion of the head during an impact, especially during an oblique impact. Previous helmets were not designed to protect against this type of acceleration. In theory, reducing the amount of rotational acceleration should reduce the damage to the brain. Our community have discussed MIPS here and here. In summary, lab tests do show that MIPS helmets reduce the amount of angular or rotational acceleration in the test setup. However, lab tests cannot precisely replicate real-world conditions, and it is impossible to do real-world randomized experiments comparing MIPS to non-MIPS helmets.

Answer 11

Boot, Tyre Boot

A firm but flexible piece of anything that can be inserted between a tyre and a tube, to provide additional support at a damaged point. If the tyre is cut, gashed, or torn to the point your tube is visible, it will puncture again in short order, and that puncture is likely to be explosive not gradual.

from Rear Tyre torn at rim - what was the cause?

Also, small holes in the tread can give punctures too, as the tube bulges out and wears off on the road surface.

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Park makes a boot, called the TB-2 which is similar to an oversized sticker pre-glued tube patch, but is intended to stick to the inner wall of the tyre.

However the enterprising cyclist can use many different items as a boot.

• An empty gel wrapper is a common choice (but clean it well, the content will go everywhere even if you think it is empty!)
• If your country uses polymer banknotes they can work, but not paper notes,
• Any item of flexible plastic from your tools
• Strips of duct tape

Tubeless tyres might benefit from a boot, if the damage is too large for the sealant to plug. However it could be hard to get the boot to lie in the right place for long enough.

Relevant questions: What's the point of tyre boots?