How to choose a rear derailleur on a bike

Spring direction

The standard operating procedure for a spring is when the chain is thrown onto the larger stars by force from the shifter, and to the smaller ones by the spring. This principle is universal, and so far, the reverse device, when smaller stars correspond to a lower number on the derailleur, remains an experiment of Shimano, losing to the classics in resistance to dirt and damage.


The rollers in the gear selector are different, and when repairing or cleaning, it is very important not to confuse them, since the life of the chain depends on this, and the switch itself.

The guide roller, aka G-pulley, or guid pulley, is upper. performs several tasks at once:

  • Directs the chain to the stars.
  • Compensates for backlash due to small horizontal displacements.
  • Increases feed smoothness and reduces noise due to small grooves on the teeth.

Bicycle Equipment : How to Choose a Rear Derailleur on Mountain Bikes

T-pulley, also known as tension pulley, is a tension pulley that prevents the chain from sagging.

Repair and installation

The switch may need to be repaired in several cases:

  • Rooster repair. if the damage was on it, and not on the switch itself. we dismantle and fix it.
  • If the rollers are loose or damaged.
  • When the frame was bent.

Everything is corrected either by replacing the element (roller), or by straightening the bent parts, and sometimes by simply replacing the product. The most important thing is to correctly install the rear derailleur, our separate article is about this procedure.

Switch operation

When the cable is pulled, the frame is pulled under the chain so that the links enter the other sprocket, changing the speed. In the opposite direction, the cyclist looses the cable, allowing the derailleur spring to return the frame to a position above the adjacent sprocket.

The second function of the switch is to maintain the sagging part of the chain, which is released when operating at lower than maximum stars.

All that is required from the frames and the parallelogram mechanism is precise movement and sufficient durability.

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Sizes and types

Let’s move on to the mechanics. Of course, all cyclists are aware of the lineup. They are vividly named and promoted, but under each sub-brand there is a number of technical characteristics, which we will now consider.

Principles of operation and maintenance

In the end. a little about the switch operation procedure.

Reaction to the rope

Many people have heard that derailleurs for bikes Shimano and SRAM. the leaders in the production of these devices. are not compatible. The reason for this is simple. different gear ratios are used in their products. If SRAM has 1: 1, i.e. when pulling the cable by 5 millimeters, the frame is also shifted by 5 millimeters, while for Shimano it is 2: 1, i.e. when the cable is displaced by 5 millimeters, the frame will move by 10 millimeters.

So far, there is no sustainable proof of the advantages of a particular system, but versatility and interchangeability continues to suffer, including due to the emergence of new transmissions for 10-speed cassettes that do not work with the shifters of even their titular manufacturer.

Mount types

The de facto standard for mounting rear derailleurs is the cock. The cock is a small bracket that is designed to protect the rear derailleur and reduce the force of impact to the derailleur and frame. In fact, a small fuse, because you can often hear that it is not the frame, but the bicycle cock that is bent and needs to be replaced.

Rooster frames usually have a special eyelet, most frames come with a ready-made rooster. In some cases, it is not removable, i.e. repairs will require welding, but on most models it can be easily dismantled and replaced. Professionals recommend keeping a close eye on the bike cock, as its deformation completely changes the mechanics of the drive system, and always for the worse, leading to wear and damage to components.

In addition to the standard, a feather mount is used. a frame element used in professional downhill bikes and various sports models to increase reliability on difficult tracks.

A few years ago, Shimano patented Shadow technology for a more compact derailleur mount, but structurally remains one of the non-standard cock mounts.

Determining which SRAM mountain bike derailleurs are best performing

The range of CPAM equipment is divided into 7 groups.

  • X3 / X4. Amateur grade products identical to Shimano Altus / Acera respectively.
  • X5. In SRAM’s lineup, this group is marketed as Shimano’s Alivio: equipment for advanced amateurs and avid cyclists. A distinctive feature is an excellent value for money. Follow the instructions on how to adjust the rear derailleur. X5 owners will have to only a few times a season. the product retains the programmed settings for a long time, but works moderately in a dirty state.

When analyzing which derailleurs on a mountain bike are the best, it’s worth keeping in mind that XX is the top line in SRAM’s range of components. This equipment is recognized as the best in the world. CPAM XX components are fitted on the bikes of world-class cycling stars.

How to choose a rear derailleur for your bike

Spring direction

The most common design of rear derailleurs (top normal), the one in which the chain is tightened on large sprockets with 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 road derailleurs, SRAM derailleurs and most Shimano mountain derailleurs work.

In 2003, Shimano released an inverted rear derailleur (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 conventional shifters, smaller numbers correspond to smaller sprockets and the up / down gears on both shifters are the same. This can be handy for beginners to learn. The main disadvantage is that this design has less resistance to dirt.

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Gear ratio of the drive of the switch of speeds

Switch Drive Ratio. The ratio of the switch movement to the corresponding cable movement. Shimano uses a 2: 1, SRAM 1: 1 ratio in its shifters and rear derailleurs, which is why the 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 dirty cables, there has been no practical evidence of this. And according to cyclists, SRAM derailleurs work harder than Shimano.

The situation is now further complicated by the introduction of ten-speed drivetrains from Shimano and SRAM. Neither are compatible with 9-speed counterparts from 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 straight bar hybrid shifters that are compatible with classic derailleurs (R-series).

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 cassette. 10-speed mountain derailleurs, however, are generally not compatible with cassettes of 9 stars or less.

Cable feed to the rear derailleur

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

  • traditional cable routing. the cable connects to the derailleur at the back, and describes a loop around the dropout (bracket on the frame for attaching wheels).
  • direct cable entry. the cable is connected to the switch from the top. In this case, the cable is laid along the shortest path.

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

Originally only SRAM had direct wired rear derailleurs, while Shimano had conventional derailleurs. In order to bring the cable directly to a traditional switch, you can use a special device avid rollamajig, which brings the cable to the desired angle. New Shimano derailleurs use a direct connection method.


The bike‘s rear derailleurs have two plastic rollers: a guide (top) and a tensioner (bottom). 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.

A bit of boring theory

The rear derailleur mechanism throws the chain over the cassette stars, allowing you to lower or increase gears (for reference, it was invented by the Italian Tullio Campagnolo back in 1950). This device also keeps the chain taut. Since the invention, many varieties have been created. A little about the main, most characteristic features.

  • Manufacturing material. From steel to carbon. The entry-level models are equipped with steel, and not always of good quality, and plastic. In the right hands, these switches even work sometimes. Models of the middle category are in most cases made using aluminum. The most expensive models can boast not only precision in work, but also titanium, carbon or composite.
  • Frame size. In theory, everything is simple. the longer the frame, the more gears you can select. However, one cannot say so categorically, since someone will prefer a short frame that is not afraid of stones, while others are interested in greater comfort in switching. And everyone is right in their own way.

You can still describe in detail the action of the spring or the options for the location of the cable for a long time. However, many good articles have been written on this topic. I will only note that there is not much difference from which side the cable enters the switch. So, now about the interesting.

How to install a rear derailleur on a bike?

Having clocked many kilometers on a bike, I was convinced that a branded derailleur is much more important for a comfortable ride than stylish grips or leather Brooks. But it’s not enough just to get Shimano or Sram, the quality of installation and setup is important.

Installation and adjustment

Reference: The Shimano Tourney TX is the entry-level model, although the exterior design suggests a higher class.

And to put something more serious on an inexpensive bike used only for riding exclusively on asphalt. meaningless. Switching range was important, however, as the city is teeming with hills, hills and mountains.

So, replacing the rear derailleur begins with removing the old noname from the frame. it’s time for Shimano. The chain link is revealed. If this is not the case, then you need to use squeeze.

The old switch is unscrewed and removed, and a new one is hung in its place and screwed to the cock. protruding triangle with a hole in the frame. It is worth tightening well, but without undue enthusiasm.

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We put the bike chain on the smallest star. Visually, the roller and small sprocket should be on the same line. The small star is the highest speed, therefore we adjust the position of the roller with the screw H.

Help: the letter H is an abbreviation for high gear, that is, top gear.

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The next step is to insure against the possibility of the chain hitting the spokes, which is likely if the derailleur goes behind the largest sprocket. To do this, you need to move the switch to the largest star, carefully and without unnecessary effort. In no case by the roller, the mount of which is very easy to bend.

The adjusting screw fixes the position of the switch exactly so that it is opposite the large sprocket. Going behind it is fraught with the loss of knitting needles and good mood. If the switch is too tight, there will be no lower gear.

Queue for the cable. he should be free to wear a shirt. We check the progress and the absence of creases. On this switch model, you can see the place for the cable to pass. We put the chain on the smallest sprocket, tighten the cable to remove the slack, fix it. Thus, installing the rear derailleur and adjusting it are two integral, complementary processes.

Now check the operation of the entire mechanism. There should be no pronounced clicking sounds when pedaling from the rear derailleur side. Switching up / down must be accurate, without skipping and delays. And even if everything fell into place, it works accurately, quietly and without delay. for the first trip it is worth taking a screwdriver with you. Working with a load may well require minor adjustments.

I note that you will have to face such a concept as preventive repair of the switch, regardless of its price category. As the rollers, which are consumables, wear out, their timely replacement will be required.

It is believed that installing and adjusting the rear derailleur is much easier than the front derailleur. However, you will have to spend time and effort, but this work will pay off handsomely during the trip.

How to choose?

The choice of gear shifter on a bicycle primarily depends on the price issue. However, it is important to consider some technical characteristics. One of the most important is the type of attachment. The following mounting options are currently available:

  • clamp to the frame tube;
  • on a special site;
  • on the carriage of the bicycle.

It should be borne in mind that the last two options are quite rare guests on the modern market. When fastening with a clamp, take into account the thickness of the bicycle frame.

When choosing a derailleur, it is also important to choose the type of steering cable wiring. Most often, the cable is pulled to the speed selector or down the bottom tube under the carriage or the top tube of the frame. Thus, there are universal derailleurs, as well as top or bottom pull.

Another important point is the parameters of the star system. The most common are two or three speed systems. It is also important to know the number of stars in the rear derailleur as the chain thickness depends on this. It is better to take into account the dimensions of the largest sprocket, the capacity of the system, the minimum difference of teeth on the large and medium sprockets, the length of the carriage axis and the angle of the chainstays.

Installation and adjustment

Setting the gear selector is not an easy task, and especially for a beginner, it will be very difficult to cope with it. Better to leave it to a specialist. But the rear and front derailleurs should be learned to set up yourself. This requires a number 5 hex wrench and a Phillips screwdriver. Tuning is most convenient when the bike is in a wheel-up position.

Rear derailleur adjustment is as follows.

  • The chain is thrown to the smallest sprocket by pressing the shifter on the right side of the handlebar.
  • Next, the switch is unlocked by releasing the screw that holds the cable. This is done by unscrewing the screw marked H with a screwdriver.
  • This screw adjusts the sprockets holding the chain so that they are positioned along the same mowing line.
  • Now you need to pull the cable, and then fix it using the screw.
  • Next, the switch is checked for proper operation. If necessary, you can improve the transition to large stars by turning the thumb counterclockwise.
  • By pressing the shifter, the chain is shifted to the smallest sprocket.
  • Use the screw marked L to set the switch position so that the largest sprocket and the switch foot are on the same line.

Front derailleur adjusts slightly differently.

  • The shifter moves the chain to the smallest sprocket in the front and the largest sprocket at the back at the same time as the pedals are pressed.
  • Next, the screw holding the cable is released. This is done with a hexagon.
  • With the screw marked L using a screwdriver, move the frame so that the distance between its inner part and the chain is about 4 mm.
  • Then the cable is pulled and the screw is tightened that holds it.
  • To debug another star, you need to throw the chain back to the minimum star, and leave it on the smallest in front. If the chain touches the frame, then you need to adjust the cable with a thumb, which is located on the left side of the steering wheel. It is worth remembering that the lamb must be mixed counterclockwise.
  • The third sprocket is adjusted with a screw marked with an H and a screwdriver.

Popular brands

The most popular brand currently is Shimano. This company is known for producing a wide variety of switches, ranging from the cheapest to professional models. Many models from the manufacturer Shimano allow you to choose the best option for any bike: road, city or mountain. For beginners, a Sora or Tiagra model is a great option.

Among the popular manufacturers, it is worth noting Sram. This company manufactures speed switches in different price segments. The main difference is the lack of thematic lines. Among the simplest and cheapest are the X-3 and X-4 models, and among the highest quality X-7 and X-9.

Shimano’s main competitor in the near future is the Taiwanese manufacturer Microshift. The main feature of the company is good quality at low prices. Many European countries have already appreciated the speed switches of this company. It is worth noting that among the advantages of this brand there is another very important one. full compatibility with Shimano derailleurs. This plus can be used very profitably during repairs.

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For lovers of the highest quality, you should pay attention to the German manufacturer Rohloff. Its planetary hubs are carefully selected and assembled by hand only. The advantages of the products of this company are huge, but it will also be quite expensive to pay for them.

Description and purpose

The greatest cycling comfort and excellent energy savings are provided by a gearshift or derailer. With it, you can choose the optimal travel mode, which is fully suitable for a specific route. The switch is especially useful if the track changes from asphalt to off-road.

You also have to use the device when accelerating, braking smoothly, and climbing uphill. It is worth noting that thanks to the switch on the bike, you can maintain a constant speed, which is very convenient when overcoming long distances. Difficult weather conditions such as strong winds or slippery tracks are also easier to handle with a derailer. It’s no secret that the bike is a great cardio trainer, which is greatly facilitated by the speed switch.

Derailer, which we know today, was invented in the 50s of the XX century by an Italian cyclist. The classic design is a block of stars. The unit that is installed in the front is called a system, and that in the back is called a cassette. The gears are shifted by shifting the bike chain to the side, which ultimately allows the chain to lie on the selected sprocket.

All stars differ in diameter, and the chain has a fixed length. Thus, it sags, but this moment is removed by a special tension spring, which is located on the rear of the switch.

Typically, bicycles have 1 to 3 leading sprockets and 3 to 12 driven sprockets. This number creates over 30 speed combinations. Of course, some transmissions can be repeated.

The switches are controlled by cables. The tension of the cables can be adjusted using the shift knobs. There are shifters on the steering wheel that pull the cable. When you press the shifter, the frame is displaced, and the chain is thrown to the adjacent star.

There is also an option where the switch looks like a drum that simply spins to the desired speed mark. The bicycle derailleur can also be made in the form of a trigger or a combination handle. Recently, electronic shift control is gaining popularity, which allows you to shift through all the stars at once.

It is worth taking a closer look at how a traditional gearshift works. The system speeds are located on the left side of the rudder handle, and the cassettes are located on the right side. When shifting the chain from one chainring to another, it is important that the pedals rotate. Also, it is impossible to pedal back in the process of switching between speeds so that the chain does not jam and the transmission does not break. It is worth noting that there is no rear derailleur on models with foot brakes.

Modern manufacturers present different types of switches that are created for different types of cycling.

  • The external derailleur is the most common type and consists of a front and rear derailleur. This option works by throwing the chain between the stars through the frame. The advantages of this switch include lightness, clear design, and a large number of speeds. Also, energy is not lost due to friction of mechanisms inside.

However, it must be taken into account that such a switching system is subject to weather conditions. Over time, the chain will wear out due to strong skew. Gears can only be changed while driving, and it is important to protect the bike from falling. Among the disadvantages, users also note the need for frequent maintenance.

  • An internal or planetary derailleur is a mechanism that sits on the inside of the hub at the back. It has only one star in the back and front, and a chain. The number of speeds in such models starts from 3. Most cycling models with planetary hubs are also equipped with a built-in brake system, which is very convenient.

The advantages include high resistance to adverse weather and bad roads, high reliability, durability, ease of maintenance. Also important is shifting gears without pedaling. In doing so, you need to know that the internal switches have an impressive weight. In such models, excessive friction of the nodes occurs, which leads to difficulties in movement. Among the minuses, it is worth noting the complexity of the repair.

  • Combined. a hybrid of planetary and external switches. Most often they are equipped with urban models of bicycles. This type is characterized by the pros and cons of both switching mechanisms.

Bicycle speed selector: types and choices

Modern bicycles are equipped with gearshift switches, which are especially useful when riding on varied terrain. Of course, in order to understand which switch option to choose and how to properly care for it, it is better to familiarize yourself with it and its features in more detail.

Subtleties of operation

The gear shifter on a bicycle works precisely and for a long time if it is used correctly. To do this, you should familiarize yourself with some recommendations. For example, switching between speeds should be done exclusively while cycling. It is also recommended to reduce the pressure of the feet on the pedals when changing gears, especially this will facilitate the condition of the front derailleur.

Before going uphill, it’s best to change gears ahead of time. This advice should be followed by beginners who do not yet know how to feel their transport. Also, do not shift multiple gears at once. The transition between gears should be carried out gradually so that the chain has time to jump to the previous sprocket.

It is important to learn not to over-skew the chain. This happens when using small or large chainrings and chainrings at the same time.

How to choose a bike derailleur in the video.