How To Choose A Rear Derailleur For A Bike

How to choose a rear derailleur for your bike

First of all, it will be useful to answer the question: “And why are there gear selection mechanisms on a bicycle? ” The fact is that the correct choice of gear allows you to vary the cadence (cadence) and the effort on them for the most efficient distribution of energy. This happens by changing the gear ratio between the pedals and the wheel. For example, when driving up a steep hill, you need to select a gear lower: in this case, the effort required to press the pedal will decrease, although the number of pedal revolutions required to drive up the hill will increase. If, on the contrary, you are driving down a steep mountain, then you must select the highest possible High gear, which will allow you to develop maximum speed. It was in order to change gears on the go that various types of switches were invented.

Internal shift mechanisms (planetary hubs)

On a bike equipped with this type of derailleur, you will NOT see cassettes with sprockets of different sizes and with a different number of teeth, and hinged derailleurs. As a result, the wheel drive has only one sprocket at the front, a chain and one sprocket at the back. How then is gear selection ensured? The fact is that the entire mechanism in this case is inside the rear hub.

Appearance of planetary hub Structure Planetary hub

Currently, a fairly large number of planetary bushings are produced with various numbers of gears (from 3 to 14). In addition, the vast majority of planetary hubs have a built-in brake. These gear shifting mechanisms are most commonly used on road and walking bikes, although sometimes they can also be found on mountain bikes.

The advantages of planetary bushings are:

  • Resistance to adverse road and weather conditions, due to the fact that the switching mechanism is completely in the housing;
  • Built-in brake;
  • High reliability and durability;
  • Ability to shift gears rather than pedaling;
  • Ease of service.

However, there are significant disadvantages to planetary hubs:

  • High weight;
  • Strong friction between knots, which complicates movement;
  • Repairability in field conditions.

Switch types

All bicycle derailleurs can be divided into two main types:

  • Internal gear shifting mechanisms;
  • External gear shifting mechanisms;
  • Combined mechanisms.

External switching mechanisms. Front derailleur.

Its task is to move the chain from one chainring to another. The principle of operation of such a switch is very simple: a chain passes through a frame that moves thanks to a parallelogram mechanism. If it is necessary to switch, this frame moves and takes a position above the corresponding sprocket, as a result of which the chain also jumps to it.

Shimano deore XT front derailleur

The front derailleurs differ in several ways, as shown below.

  • Method of attachment to the frame. Most often, fastening with clamps is used. Moreover, the clamps themselves can be designed for different diameters of the seat tube, which should be taken into account when purchasing. However, there is a mounting method in which the plate holding the switch is clamped by a carriage or cartridge in order to be able to install the switches on frames with non-standard geometries.
  • Installation angle of the frame. If this parameter is selected incorrectly, a situation may arise in which the derailleur frame touches the bike frame. In this case, correct gear shifting becomes impossible.
  • Method of fastening the cable. The drive cable, depending on the method of attachment to the bike frame, can be brought to the switch from the bottom or from the top. There are universal models of switches, which are designed for two connection methods, but there are also those that are designed for only one.

In general, all front derailleurs have one significant drawback: they are practically NOT capable of transferring the chain from one chainring to another under load (especially from a smaller chainring to a large one). Manufacturers are trying to solve this problem, as a result of which various systems appear that use pedaling energy for shifting. However, they are expensive and not very efficient.

15. Chain

The chain is the most complex mechanical device in a bicycle. The chain is constantly subject to wear and is subject to constant maintenance, lubrication and timely replacement.

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How much does a bike rear derailleur cost?

The for switches can be completely different depending on the manufacturer and the materials from which the part is made. So, but a professional part of good quality can cost in the region of 3500-5000 thousand rubles. In the trialzone.Ru website catalog you can find Not only budget models, but also more expensive ones. for real professionals. It is always worth remembering that the reliability of spare parts is often directly proportional to its cost.

This is the most important part of the bike. You can change parts as much as you like, but changing the frame is tantamount to changing the bike. Geometry, materials, pipe cross-section parameters and welding quality. all this must be given great attention when choosing a bicycle.

Shimano Altus (Shimano Altus)

Neither fish nor fowl. The most controversial line of switches in my opinion. They are NOT much better than the Tourney in terms of speed and shifting accuracy, I would say that one of the few differences is the ability to use modern models on a cassette with 8 stars (9 stars since 2012). The main difference from the Tourney is great durability, for little money. A good option for those who rarely ride, short-term and close.

Pros: low price, acceptable durability.

Cons: low accuracy and low reliability, the chain still bounces on the sprocket from shaking and hits the lower frame.

In the road range corresponds to the Shimano 2300 group.


Rim brakes. Caliper brakes are V-brakes or cantilever brakes that clamp the rim of a bicycle wheel.

Connecting rods

This pair of pieces of iron are the very levers that your feet push when pedaling. It is clear that they must be quite strong under serious acceleration. Advanced XC models use durable lightweight cranks.

How To Choose A Rear Derailleur For A Bike

Shimano Alivio (Shimano Alivio)

This line is already suitable for quite serious hikes and amateur competitions, but the chain still hits the lower feather on bumps. A kind of fine line of transition between the amateur and professional level. The switching quality is already quite fast and accurate, plus work with cassettes of 8-9 stars. His reliability is also acceptable, but nevertheless this “edge” is felt and the transition is felt. The Alivio is ideal for those aiming for frequent rather than aggressive riding in all weather conditions, without regularly adjusting the switch.

On-road matches Shimano Sora group.

Mount on the frame

There are 2 ways to attach the rear derailers.

  • Under the hook. attachment to the bicycle hub. This is a fairly reliable mount, but if the rear derailleur accidentally breaks down, the bushing also fails, which entails additional costs;
  • Under the bolt. The rear derailleur is attached either to a hole in the VELOBIKE frame, or through an adapter called a “rooster”. The advantage of such a device is that when dropped, neither the switch, nor here is damaged, but only the adapter. Naturally, repairs will be much cheaper than in the previous version.

Rear hub

Attaches the rear wheel, provides rotation and carries a ratchet or cassette. Cassette bush is stronger than ratchet bush.

Shimano Hone / Zee (Shimano Hone / Zee)

They are essentially the same switch level. Until 2008 he came out under the name Hone, now it goes under the name Zee.

The lowest level of derailleurs, designed for use in extreme disciplines, for example, in “gravity”: Down Hill, Free Ride, Dirt, etc. But do not be confused by the word “lower”, since the level of the derailleur is between Shimano Deore LX / SLX and Shimano Deore XT. Accurate, fast, reliable, with emphasis on impact resistance and high shock loads.

Liked? Share with your friends and rate the recording:. Spring direction

The most common option is Top normal (shifting with a cable is performed from a small sprocket to a large one). Most manufacturing firms adhere to this principle. In addition, there is a Low normal direction, or the opposite, with the chain dropping onto small sprockets. Switching to large sprockets is possible with a spring. This device is only available on the Shimano range of bicycles. There are significant advantages in reverse switching, therefore such products are NOT very popular.


The rear derailleur is a complex part that deserves special attention in both selection and maintenance. If everything is done correctly, then you will get maximum pleasure from cycling.

Purpose of the rear derailleur

The rear derailleur or derailer is a gear shifting device that makes it possible to move the chain passed through the rollers and frame along the ratchet sprocket or rear cassette. A large chain is thrown when the switch moves along the axial part of the ratchet or cassette. In addition, it is possible to move the device in a vertical plane to maintain a constant spacing between the roller and rear sprockets.

Most often, the bike‘s rear derailleur uses a cable-type drive (it can be electric or hydraulically). Switching the device from small sprockets to large ones is carried out by pulling the cable, and in the opposite direction by pulling the chain.

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It is necessary to perform gear switching during the pedaling process, large, with a minimum load. In this case, the rear derailer will last longer, and the transition from one speed to another will be clearer.

Gear ratio

It is the quotient of two movements: the cable and the derailleur. It can be:

  • 1/1. Sram;
  • 2/1. Shimano.

Therefore, bike transfers from THESE companies are not interchangeable. At the same time, the clarity of speed switching is approximately the same.


Designed to tension and guide the bike chain. There are 2 types of rollers.

  • Guides;
  • Stretch.

As a rule, they are made of plastic. Since they wear off significantly, they require periodic replacement. With the wear of the VELOBIKE rollers, the quality of gear changes deteriorates. Idler and idler rollers are not interchangeable parts. In addition, the rollers from different bicycle companies also do not match.

How to choose the right rear derailleur

The gear selector is large. an important detail for different bike models, be it urban or mountain modifications. This is the state of the device depends Not only on the pleasure you get from cycling, but also on the safety of the ride. Therefore, before starting the cycling season, you need to check that this unit is working properly. To do this, you need to have an idea of ​​what a rear derailleur device is. This will be discussed in the article.

  • Purpose of the rear derailleur
  • Features of the choice of the rear derailleur
  • Rear derailleur materials
  • Rollers
  • Rear derailleur designs
  • Frame length
  • Spring direction
  • Gear ratio
  • Mount on the frame
  • Protection methods
  • Feature of operation of the rear derailleur
  • Outcome

Rear derailleur designs

Rear gearshifts are large periodically worn out. When the question arises of replacing the derailer, you must NOT be mistaken with the choice. All switches are classified according to these criteria.

Rear derailleur materials

Factors such as the cost of the BIKE, its strength and weight depend on what kind of metal the rear bicycle derailer is made of. The most affordable option is a steel alloy derailleur for budget bikes. The disadvantage of such a device is susceptibility to deformations, and the strength characteristics are not the best. Much better options are.

  • Titanium;
  • Carbon fiber.

The frame is made of carbon and the spring is titanium. Of course, such devices are used in expensive high-end VELOBIKES.

Rear gearshifts based on aluminum alloy are a kind of compromise between the above options. In this case, the individual components (for example, the spring) are made of steel.


This is the material from which the rear derailleur of the bicycle is made depends on its strength, durability and price. Switches can be divided into the following categories based on materials of manufacture:

  • Steel is used in the lowest level rear derailleurs. These switches are usually the cheapest, but also the most short-lived.
  • Aluminum alloys are used in the mid-level rear derailleurs. Some parts in such switches can be made of steel (adjusting bolts, return spring, one of the frame cheeks).
  • The toughest and most expensive switches have a titanium spring and carbon frame.

Gear ratio of the drive of the switch of speeds

Switch drive gear ratio. The ratio of the switch movement to the corresponding cable movement. Shimano uses a 2: 1, 1: 1 ratio in its shifters and rear derailleurs, which is why THESE rear derailleurs are NOT interchangeable (although SRAM makes some shifters compatible with Shimano derailleurs). Although SRAM engineers claim that their 1: 1 system provides better performance in tough conditions and with cable contamination, there has been no practical evidence of this. And cyclists say SRAM’s derailleurs work harder than Shimano.

The situation is now even more complicated by the introduction of ten-speed drivetrains from Shimano and SRAM. Neither are compatible with 9-speed counterparts of the same firm, but SRAM’s 9-speed drivetrain is compatible with Shimano’s 10-speed Dyna-Sys mountain range. However, Shimano’s 10-speed road shifters and derailleurs are still designed for classic cable travel (2: 1), so there are naturally 10-speed ‘hybrid’ straight bar shifters that are compatible with classic derailleurs (R-series).

Spring direction

The most common design of rear derailleurs (top normal), in which the chain is pulled on the large sprockets by a cable (by the force of the cyclist), and in the opposite direction the chain is pulled together by a spring. This is how all SRAM road derailleurs, derailleurs and most Shimano mountain derailleurs work.

In 2003, Shimano released a rear derailleur with “inverted” design (Rapid Rise or low normal). With this design, the cyclist, by means of a cable, drops the chain onto small stars, and on large ones it is tightened by a spring. The only plus of such a switch is that on a conventional shifter, smaller numbers correspond to smaller sprockets and the up / down gears on both shifters are the same. This can be convenient for beginners to learn. The main disadvantage is that this design has less dirt resistance.

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Cable feed to the rear derailleur

This figure is determined by the way the cable jacket is attached to the switches. There are two ways:

  • Traditional cable routing. The cable connects to the derailleur at the back, while it describes a loop around the Dropouts (bracket on the frame for attaching wheels).
  • Direct cable routing. The cable is connected to the switch at the top. In this case, the cable is laid along the shortest path.

Direct cable lead is much better than the traditional one, with it there is a bend in the cable, and therefore there is no chance of it catching on any obstacle, and weight is also saved.

Originally only SRAM made rear derailleur rear derailleurs, while Shimano had conventional derailleurs. In order to bring the cable directly to the traditionally switch, you can use a special device “avid rollamajig”, which proved the cable at the desired angle. New Shimano derailleurs use a direct connection method.

Rear derailleur frame length

There are three standard frame lengths that define such an indicator as “switch capacity”. The range of gear ratios with which the rear derailleur can work. A longer frame length allows you to select a switch with a larger chain slack. Big “capacity”.

If expressed in the second, then “speed switch capacity”. it is the sum of the difference between the largest and smallest sprockets of the cassette and the system that the derailleur can handle without sagging or binding in the chain. For example, if the bike has an 11-32T cassette and a 22-32-44T system, then the minimum permissible capacity of the rear derailleur is calculated as follows: (32-11) (44-22) = 43T.

If you install a speed switch whose frame is shorter than required, then the chain will be loose on the front small and rear small sprockets (if the chain length is selected correctly).

Installing the rear derailleur with a too long frame will not affect the derailleur operation, but it will add weight and risk the derailleur frame hitting an obstacle. Some cyclists deliberately choose a shorter frame to avoid hitting obstacles, but whether this makes sense is not yet clear.

The exact values ​​of the capacitance of the rear derailleurs can be found in the manufacturers’ catalogs, but we will indicate an approximate rule for choosing the frame length:

  • Short Frame: MTB Single System (Extreme Bikes), Dual System Road Bikes;
  • Middle Frame: MTB Dual System (2×9, 2×8), Road Bikes Triple System (or Dual System and Mountain Cassette)
  • Long frame: MTB with triple system (also 2×10 with cassettes type 11-36) and other options.


The bike’s rear derailleurs have two plastic rollers: a guide (upper) and a tensioner (lower). On some models of rear derailleurs, these rollers are not interchangeable with each other. There is also a difference between rollers from different manufacturers and different models of switches from the same manufacturer. The rollers are mounted on plain or rolling bearings and are consumables. They wear out faster than the switch itself, bearings loosen and teeth grind. In this case, they should be replaced with new ones, otherwise the clarity of the gear shift will disappear.

Shadow technology

This technology was developed and patented by Shimano. It allows you to reduce the lateral protrusion of the mechanism when riding on small sprockets. The company says this reduces the chance of damage to the rear derailleur or cock from a fall on its side. Also, such switches use a more direct cable feed.

Differences between bike rear derailleurs

If it becomes necessary to change the rear derailleur, the question of their compatibility arises, since there are models of derailleurs that have up to six or more varieties, different in design.

First of all, we note that the rear derailleurs with 7-9 stars are interchangeable, therefore it is possible to use a derailleur from a 9-star cassette to 7-star. 10-speed mountain derailleurs, on the other hand, are generally not compatible with 9-star cassettes or less.

The principle of operation of the rear derailleur

Rear derailleur. This is a parallelogram mechanism with a powerful spring, which moves the frame along the axis of the cassette ( “foot”) with fixed rollers. The speed switch is set to “cock” with a hollow bolt and can swing up and down to maintain a constant distance from the idler roller to the cassette stars. Shifting gears in one direction is carried out by pulling a cable, hydraulic or electric drives. In the opposite direction, the switch moves under the tension of the chain passed through it.

Switching speeds is possible only when pedaling forward. When switching speeds, try to reduce the load on the pedals, although switching is possible and under heavy load this is undesirable, as it can lead to accelerated wear or damage to the parts of the switch.