Glossary: A Brief Explanation of Shifting Technologies

In the case of bicycle shifters and derailleurs, there are countless technical designations, marketing terms and registered names that are not always easy to distinguish from one another. Sometimes the same things are given a different name by various manufacturers, sometimes there are multiple technical solutions that address the same problem. However, the basic functions and components of a derailleur are always the same: chainring, sprocket, chain, rear derailleur and shift lever.
In our glossary, we’ll explain how these parts work together and which are the most important terms you should know.

Bolt Circle Diameter

The bolt circle diameter is a straightforward indication of the compatibility of chainrings. (Exception: 94 mm with four and five screws exists.) The dimension describes a circle through the centre of all chainring bolts. In the case of four-bolt mounts, this is easy to measure with the distance between two opposite holes, while five-bolt mounts can only be calculated: multiply the measured distance between two chainring bolts by 1.7 to get the bolt circle diameter.

Bowden Cable

The Bowden cable (named after its inventor, Ernest Monnington Bowden) is a steel cable that mechanically transfers the action of the control from the shift lever to the rear or front derailleur. A Bowden cable consists of many thin steel cable strands twisted together. The shift cable housing acts as an abutment for the cable, which is why it must be routed continuously from the shift lever to the rear derailleur or interrupted by paired cable stops on the frame. To shorten the Bowden cable (and the housing) you need a suitable pair of pliers. Shift cable housings are fitted with steel longitudinal cores and brake cable housings with a coiled reinforcement made of steel. Brake cables are not compatible with shift cable housings. You can recognise shift cables by the (smaller) longitudinal barrel at one end, brake cables by the (larger) transverse barrel or a pear-shaped barrel for road bike brake levers.

Brake Lever

In the shift/brake lever, brake lever and shift lever are combined into one ergonomic unit. They are also referred to by the English term "brifter" or "STI" after Shimano's Total Integration technology. Its original purpose was to integrate the gear lever on the road bike handlebars. They come standard on contemporary road bikes; there are versions for electronic and cable shifting systems as well as hydraulic and cable brakes. On the mountain bike, integration has been abandoned again, as this makes it easier to combine components from different manufacturers.

Capacity

The capacity is a very precise indication of the range of all gears of a shifting system. Mostly, the capacity is needed to find out the compatibility of rear derailleurs. It is calculated from the difference between the teeth on sprockets and chainrings. With 1x drivetrains, the capacity is easy to see: a cassette with 10-52 teeth has a capacity of 42. For example, for a 3 x 9-speed shifting system, calculate as follows: at the cassette (11-32) 32-11=21 and at the crank (46/36/24) 46-24=22, resulting in a capacity of 43.

Chainline

The chainline indicates how many millimetres the chain runs on the chainring to the right of the frame’s centre. To enable greater tyre clearance on mountain bikes, the Boost standard was developed, which not only made the hubs wider, but also shifted the chainline outwards by three millimetres. For more in-depth information, see our article on hub standards and Boost.
On bikes with derailleurs, the chainline varies: with multiple chainrings front and rear, with 1x drives only rear. Extreme skewing of the chain should be avoided to prevent excessive wear.
The precise adjustment of the chainline is of particular importance for belt drives, hub gears and singlespeed bikes as well as fixies.

Chainring: Direct Mount, Spider, Crank Star

Chainrings are bolted either with five or four bolts to the corresponding sockets of the right crank. These mounts can also be provided by a spider, which is bolted to the crank on a multi-tooth mount. If a single chainring or two firmly connected chainrings are mounted directly on the multi-tooth mount, this is called direct mount.

Decoupling / Impact Protection (E-Shifters)

With electronic rear derailleurs, shifting is carried out by an actuator and no longer a Bowden cable that tensions the rear derailleur against an internal coil. This is why the E-shifters can no longer automatically avoid a fall or contact with an obstacle. Damage to the rear derailleur, derailleur hanger or frame would very likely result. That is why, in such a scenario, the rear derailleur cage is decoupled from the actuator in a fraction of a second so that the rear derailleur is spared from impact. The disadvantage thus becomes an advantage as the rear derailleur’s protection increases.

Derailleur Hanger

The derailleur hanger is the M10 thread that is used to screw the rear derailleur into the frame. Since the rear derailleur has a rather exposed position, it can transmit extreme impact impulses to the derailleur hanger in the event of a fall or collision with obstacles. On frames made of steel and titanium, the derailleur hanger is usually designed as an integral part of the right dropout, as these materials allow for correction should the derailleur hanger bend from impact. On aluminium and carbon frames, the derailleur hanger is designed with the knowledge that it will eventually have to be replaced, as it is made to protect the frame in the event of damage. It is therefore advisable to keep a spare derailleur hanger in your home workshop or bring one with you on tours. There are hundreds of different derailleur hanger designs and various manufacturers. They are named according to the manufacturer and model of your bike or according to the nomenclature used by the respective manufacturer. A more recent designation is "UDH" (Universal Derailleur Hanger) from US manufacturer SRAM, which frame manufacturers are allowed to use licence-free in the hope that it will add clarity to the confusing jumble of hundreds of derailleur hangers.

Derailleur Pulleys

On each rear derailleur there are two derailleur pulleys, i.e., small cogs around which the chain is looped. They are made from aluminium or plastic, the latter of which usually runs more quietly. They usually have ten to 15 teeth, and in rare cases (upgrade cages from KCNC or the OSPW system from Ceramicspeed) up to 19 teeth. Odd numbers of teeth reduce wear. The preload of the cage in which the pulleys are located ensures a taut chain and the correct adjustment of the rear derailleur for optimal gear changes. The pulley (“guide pulley”) must be positioned exactly under the corresponding sprockets. Derailleur pulleys are often labelled according to their position and rotational direction. Derailleur pulleys wear out and should be replaced when the teeth are worn. Inexpensive pulleys rotate around a plain bearing, while higher-quality pulleys have cartridge bearings.

Derailleurs

The main features of derailleurs are the sprockets and chainrings of various sizes. To change gears, the chain is moved over these sprockets and chainrings by a rear derailleur (on the rear wheel) and, if necessary, a front derailleur (on the crank). The unprotected position of the components requires more care than is necessary with hub gears. The main arguments for the dominance of derailleurs on sports bikes are their low weight and the ability to shift under load.

1x Drivetrains

One-by (1x) drivetrains do not require a front derailleur. The name is derived from the single chainring on the crank. These shifting systems became more common, especially on mountain bikes, thanks to cassettes with a large spread, i.e. 400 to 520 percent gear spread from the smallest to the largest sprocket, which is significantly more than many two-by shifting systems offer.

E-Shifting

More and more shifters & derailleurs for bicycles operate electronically. Instead of a Bowden cable, the action of the control is transmitted by cable or radio. The shift in gears itself is triggered by electronic actuators in the rear and front derailleur, making shifting more precise and faster. In addition, the front derailleur can align itself to the position of the rear derailleur. A special feature of the technology is the required power source, which is either integrated centrally (wired shifting) or autonomously at each component (wireless shifting). Mostly these shifters offer different shift modes, flexible button settings and connectivity with smartphone, bike computer and E-bike controls. There are electronic derailleurs for road bikes and mountain bikes as well as electronic hub gears for city and touring bikes. You can find out more about this topic in our article on electronic shifters & derailleurs.

Freehub Body (XD, XDR, Microspline, etc.)

The freehub body is a central component of most hubs on mountain bikes and road bikes. It has the effect that you can apply power to the hub via the chain in a clockwise direction and thus propel the bicycle. Counter-clockwise, the freehub releases the connection so that you can roll without moving the crank. There are different types of functions and designs, which we outline in detail in another article on the subject of freehubs and freehub bodies.

Front Derailleurs: Direct-Mount, E-Type, High-Clamp, Low-Clamp, Side-Swing, Down-Swing, Top-Swing

There are different ways to mount a front derailleur on a bicycle. Traditionally and most commonly, front derailleurs have a clamp that attaches to the seat tube. The latter are available in different diameters and / or with spacer clamps to bolt them to round seat tubes of different thicknesses.
On MTBs and touring bikes, a distinction is made between high- and low-clamp front derailleurs, which simply means the design, i.e. whether the front derailleur sits below or directly next to the clamp. Accordingly, high-clamp front derailleurs are also called down-swing front derailleurs, and low-clamp front derailleurs are also called high-swing front derailleurs. Front derailleurs with side-swing technology are space-optimised and are controlled at the front. The mechanism rotates sideways in the process. Sometimes the shape of the seat tube (ovalisation, taper) and the position of the bottle cage bolts can determine the compatible derailleur type.
E-Type front derailleurs are mounted on the bicycle with two bolts, either to direct E-Type mounts on the frame or to a plate with these mounts, which is bolted directly to the frame with the right-hand bottom bracket shell. Direct mount means that the upper end of the front derailleur is screwed into a corresponding mount or suitable adapter on the seat tube.
On road bikes, the front derailleur is screwed onto the braze-on, a term based on the braze-on eyelets on classic steel frames. If your frame does not have such a mount, you will need an appropriate clamp adapter.

Front Derailleur: Down-Pull, Top-Pull, Dual-Pull or Front-Pull

Front derailleurs with Bowden cable drives are controlled either from below, from above or from the front. In the former case, the shift cable is routed on or inside of the down tube and is lain upwards around the bottom bracket to the front derailleur. The shift cable therefore pulls on the front derailleur from below (down-pull). In the second case, the front shift cable is routed on or inside of the top tube of the frame and pulls on the front derailleur from above. There are front derailleurs that operate both of these controls (dual-pull); you have to route the cable in a different way for this. In the fourth case (front-pull), the cable is also routed on or inside of the down tube, but reaches the front derailleur directly from the front, without “deviations" around the bottom bracket.

Gear Box

Gear boxes integrated into the frame have been the conceptual core of studies for many years, especially in the MTB sector. The advantages of this system are very tempting, especially off-road: encapsulated drive, ideal centre of gravity, light rear wheel and a wide range of gears. The Swabian company Pinion introduced the first gear box in series production and now offers versions with 6, 9, 12 and 18 gears. In terms of shifting behaviour, gear boxes are similar to hub gears: shifting is possible when stationary, but difficult under load. Gear boxes cannot be retrofitted because the frame must be constructed directly with the corresponding interface.

Gear Hubs

See "hub gears".

Gear Inches

Gear inches describe how much distance a bicycle effectively covers with one turn of the crank. It is calculated from the outer circumference of the rear wheel and the gear ratio of the engaged gear.

Gradation

The distance between the individual gears is referred to as gradation. The higher the gradation, the greater the effect a gear change has. Lower gradations have less of an effect on a constant cadence, which necessitates more shifting operations. Higher gradations are used more often on MTBs or E-bikes. On road bike cassettes, these tend to be lower and there are sometimes up to seven sprockets on them, each with only one tooth difference.
The gradation between two chainrings is by nature a rather large one and is therefore usually put into perspective with equalising shifting levels on the cassette. See also Linear / Sequential Shifting

Gripshift

Gripshift is the term used for twist shifters, especially on MTBs. The term is a registered brand name of SRAM, but is used across the board for all shifters that operate in this way. The technology became popular in the nineties and is still employed today for current MTB groupsets from SRAM. The right grip shifts the rear derailleur, the left grip shifts the front derailleur, if it’s there. For gear shifting from three to 18 gears, the twist shifter is the predominant principle. Manufacturers of handlebar grips often offer users of these shifters shorter versions of their grips.

Hub Gears

In hub gears (also called gear hubs) the gears are enclosed in a hub housing. This protects the shifting mechanism from external influences such as dirt and significantly reduces maintenance. There are hub gears starting at two and which go up to 14 gears. They centre the weight of the shifters on the rear wheel hub and cannot be shifted under load, but can be shifted when stationary. That is why hub gears are often found on city and touring bikes.

Lever Clamps (Matchmaker etc.)

For a neat and space-saving cockpit, many mountain bikers and touring cyclists use lever clamps. They allow you to mount gear levers or the lever on the telescopic seatpost directly on the handlebar clamp of the brake lever. Many available products are compatible with one another, either directly or with adapters; fine-tuning the ergonomics is sometimes a little tricky.

Linear / Sequential Shifting

Linear shifting describes the direct sequence of ascending or descending ratios during shifting. With 1x drivetrains, for example, you shift through gears one to twelve in succession. Sequential shifting, on the other hand, takes two or three chainrings into account: in order to engage the next gear ratio, the rear and front derailleurs must sometimes perform at the same time. There is also the case of equalised shifting levels.
With electronic shifters, you can sometimes choose between different automated shifting sequences.

Lockout (Rear Derailleur)

Modern rear derailleurs from SRAM have a lockout function called “Cage Lock”, which deactivates the chain tension. With Shimano rear derailleurs, the rear derailleur clutch is reduced for this purpose. Both are helpful when fitting and removing the rear wheel and when fitting or repairing the chain. To activate the “Cage Lock” on SRAM, turn the rear derailleur cage with the lower derailleur pulley forwards towards the crank. At a certain point, the button with the lock can be pressed and a pin locks the cage so that it can no longer move backwards. To reactivate the chain tension, simply turn the cage a little further forward until it clicks.

Master Link

The bicycle chain can be easily closed by means of a master link after it has been suitably shortened and installed on the frame. A broken chain on the road should also be repaired with a master link. It is essential to pay attention to the compatibility of master link and chain – most master links are therefore designated with numbers from "8" to "13", equivalent to the designation of chain compatibility with the number of gears. As a rule, manufacturers recommend only using master links once. It is also recommended to choose the same brand of master link as the chain. Then there are no problems in terms of pin diameter.

Mullet

Named for the hairstyle, there are two uses for the term "mullet" in cycling. On the one hand, it refers to mountain bikes with a smaller rear wheel and a larger front wheel. In the case of shifting system, one speaks of a mullet when (for example on a gravel bike) the rear derailleur and the wide-spread cassette from a mountain bike are combined with cranks and shift levers from a road bike.

Narrow-Wide

Narrow-Wide describes the tooth profile on chainrings in 1x derailleurs. The teeth are alternately narrower and wider, corresponding to the spaces in the chain links. This design ensures an optimal hold of the chain on the chainring even during severe impacts. Together with the rear derailleur clutch, it makes previously ubiquitous chain guides obsolete for most applications.

One-Piece / Multi-Piece Cassette

The cassette or sprocket set is the collection of currently up to 13 differently sized sprockets on the rear wheel through which the chain is shifted in order to switch gears. The cassette is placed onto the freehub body of the rear wheel hub and screwed on. The higher the quality of the cassettes, the fewer individual parts they contain. A ten-speed cassette, for example, which consists of ten individual and plugged-in sprockets with spacer rings in-between, leaves marks in the freehub body with each individual gear. With one-piece cassettes, the force is distributed over a broad foot, which protects the freehub body. Multi-part cassettes can be plugged in or riveted or a mixture of both. One-piece cassettes are now and then milled from a single piece, which helps save material and weight.

Rear Derailleur Cage and Parallelogram

The derailleur cage is the downward protruding part of the derailleur in which the two derailleur pulleys are located. It is put under load (see also rear derailleur damping) and thus keeps the chain taut. The rear derailleur parallelogram provides the second movement that the rear derailleur can perform: it brings the rear derailleur cage into position under the individual sprockets of the cassette. In mechanical rear derailleurs with a Bowden cable, there is a strong coil in the parallelogram against whose tension the cable moves and tensions the rear derailleur. In the case of E-shifters, an actuator takes over the function of the coil and cable.

Rear Derailleur Damping (Shadow Plus, Type 2)

Additional rear derailleur damping is intended to prevent uncontrolled swinging of the rear derailleur cage and thus chain slap. The spring mechanism of a mechanical rear derailleur has a certain degree of self-damping. Additional external damping on the rear derailleur cage is carried out via an adjustable friction clutch (Shimano Shadow Plus), a roller bearing clutch (SRAM Type 2 & 3) or fluid damper (Orbit, found in SRAM AXS wireless rear derailleurs). Damping ensures that impacts from uneven terrain cannot deflect the chain and cage until they overcome a certain breakaway torque. The tauter the chain is and the better the cage is damped, the less amount of chain slap – shifting becomes quieter and leaves fewer marks on the chainstay. In addition, the chain rests more securely on the chainring, so it doesn't come off as quickly. The rear derailleur damping has been significantly increased on rear derailleurs for 1x drivetrains, which is why the bikes then do not need a chain guide. On full-suspension MTBs, however, rear derailleur damping has an influence on the response behaviour of the rear triangle.

Shift/Brake Grip or Lever

See “Shift/Brake Lever".

Shifting Aids

See shifting pins and ramps

Shifting Pins and Ramps

On sprockets and chainrings of derailleurs, individual teeth have different heights and shapes. In the case of double and triple chainrings, shifting pins and ramps can also be noted. The aim of both is to change gears as smoothly as possible, i.e., for the chain to move over the sprockets without noise or force.

Spread (Gear Range)

The spread of a derailleur describes the difference in the gear ratio from the smallest to the largest gear and is given as a percentage. With a 1-speed derailleur with a 32 chainring and a cassette with 11 – 52 teeth, you have a gear ratio of 0.61:1 to 2.9:1 and thus a spread of 475 %.

Transmission Ratio

The transmission ratio of gears can be seen very clearly on a derailleur: it is calculated by dividing the number of teeth on the front chainring by the number of teeth on the rear sprocket. With a standard 1-speed derailleur with a 30-tooth chainring and a cassette with 10-51 teeth, the maximum ratio is 30/10, i.e., 3.0:1, and the minimum ratio is 0.58:1. The latter can also be called reduction. If you multiply this value by the wheel circumference, you get the gear inch measurement.

Trigger and Shifter

Trigger is the name SRAM gives to its mountain bike shifters with the typical two thumb buttons under the handlebars. However, the term has become established alongside “shifter” for all shifters with this functional principle. On Shimano shifters, the smaller upper switch can be pressed with the thumb as well as pulled with the index finger, which is close to the original meaning of the word trigger.

Wireless Shifting

Wireless shifting is a special form of electronic shifting in which the shifting tasks are not transmitted by cable but wireless transmission. Wireless shifters are much easier to install and give a tidier look to the bike than shift cables. However, they require a rechargeable or disposable battery in each individual component.