How to choose a rear derailleur on a bike


In the event that you need the clearest transmission and there is NO need for a rear 36-tooth chainring, then the choice is obvious. 9-speed CPAM, which has the maximum amount of transmission cable, minimum line noise and no backlash in the active joints of the switches.

If at the word CPAM you get nausea, and this, apparently, is something personal, from which the psychologist cannot save you, then the 10-speed SHIMANA will help you. A significant amount of cable per transmission (it wins over 10-speed CPAM and 9-speed SHIMANA), quite low line noise, however, there is play in the switches, but, as mentioned above, the backlashes are eliminated by the spring of the parallelogram of the switch frame, and, in addition to the shake and the unpleasant sensation that you were sold used, no problems arise.

We take the shifters from the 10-speed SHIMAN XT (.), Connect with the SRAM SWITCH FOR 9 (.) Gears, for example, X9. HURRAH. Now this can be realized, since we already know that 9-speed CPAM pulls 35 mm of cable, and 10-speed SHIMANA pulls 35 mm of cable! Yes, you can crossbreed, and, during the operation, pour all this with beer, so that there is no rejection.

  • 1.Rear shifter. nine-speed CPAM X9 (tested on two samples of 2010 and 2009)
  • 2. shifters. 10-speed SHIMANA HT 2011
  • 3.cassette. ten-speed SHIMANA XT 11-36 (.)
  • 4. chain. SLH 74ya. in short, just a ten-star chain.

Here’s what we learned from this thread:

  • 1.9-speed CPAM with 9 gears selects 35 millimeters of cable. That is, one gear selects 35/9 = 3.9 mm of cable.
  • 2. 9-speed SHIMANA with 9 gears selects 22 millimeters of cable. That is, one gear selects 22/9 = 2.4 mm of cable.
  • 3. 10-speed CPAM with 10 gears selects 29 mm of cable. That is, one gear selects 29/10 = 2.9 mm of cable.
  • 4. 10-speed SHIMANA with 10 gears selects 35 millimeters of cable. That is, one gear selects 35/10 = 3.5 mm of cable.

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

These numbers need to be kept in mind, we will come back to them later.

Now let’s forget about the speeds and pay a little attention to backlash in the rear derailleurs and errors in the impulse communication lines with the rear derailleur, in other words, about the errors that accumulate in shirts.

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Let’s start with switch play. Anyone who has held the speed switch on a SRAM and SHIMANO bike in their hands knows that SRAM has much stiffer switches. As for the XT-shnyh shifters, they, in general, go straight off the assembly line with backlash (in any case, both of mine in 10 and 9 gears could be called simply disgrace when it comes to backlash issues). Interestingly, SLH has less backlash! I held 2 models for 9 gears in my hands, and both were more “dense” than the HT.

As for the CRAM, both copies of the switches that I had the good fortune to turn in my hands. the 2010 and 2009 X9. were strong, all the moving joints were “bunched up” and did not create noise. However, the whole point is that in addition to the splitting and discomfort. in principle, the loofahs of the switches in the parallelogram connections, in the hinge of the chain tension frame and in the hinge of the switch itself, DO NOT affect the quality of the shifting in any way!!

What is the reason? Yes, the fact is that the return spring in the switch frame (the one that pulls back the cable at the moment when you drop the reverse gear to a smaller sprocket) collects these backlashes to one side, as if pressing them, and they immediately disappear and are compensated during switch configuration.

Now, regarding the error of communication lines, this is more interesting. Backlash in communication lines appears more or less, depending on many parameters. First of all, the backlash is influenced by the quality of the assembly of the communication line, and, in particular, they depend on the quality of the processing of the shirts at the edges and how much the perpendicularity of the cuts with respect to the axis of the shirt is maintained. The number of speeds does NOT affect the Backlash of the communication lines.

This means that if we consider the finished line, then at different positions of the steering wheel, bends of the shirt, etc., the cable can fluctuate about its position by about 0.5-1 millimeters, depending on how well the line is assembled.

A value of 0.5-1 millimeter, in itself, will not say anything, but now it’s time to remember the described cable samples in SHIMAN and SRAM. Now you can superimpose the value of the line error on different types of transmissions and see what percentage of the line errors (noise) can be in relation to the value of the signal itself (the length of the cable in one gear). Let’s take an average error value of 0.75 millimeters:

  • 1.9-speed CPAM. It takes 3.9 mm of cable for transmission. We observe an error of 0.75 millimeters from the signal level of 3.9 millimeters will be 19%: (100%. ((3.9-0.75) /3.9100%)
  • 2.9-speed SHIMANA. It takes 2.4 mm of cable for transmission. We observe an error of 0.75 millimeters from the signal level of 2.4 millimeters is 31%: (100%. ((2.4-0.75) /2.4100%)
  • 3.10-speed CPAM. It takes 2.9 mm of cable for transmission. We observe an error of 0.75 millimeters from the signal level of 2.9 millimeters will be 26%: (100%. ((2.9-0.75) /2.9100%)
  • 4. 10-speed SHIMAN. It takes 3.5 mm of cable for transmission. We observe an error of 0.75 millimeters from the signal level of 3.5 millimeters will be 21%: (100%. ((3.5-0.75) /3.5100%)
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UNDER THE SAME OPERATING CONDITIONS (the quality of the shifters, the quality of the communication line, backlash, and so on), the 9-speed CPAM OBJECTIVELY HAS A MORE CLEAR SWITCHING due to the fact that it has the lowest level of error relative to the signal level (sampling of the cable for transmission). 19%.

Further, according to the quality indicators of switching, the 10-speed SHIMANA follows. 21% of the error, followed by the 10-speed CPAM. 26% of the error and in the last place is the 9-speed SHIMANA with 31% error in relation to the signal level.

That’s it. I think now it has become clear to many why they write that the 9-pin CPAM is less upset, the gears need to be adjusted less often, it is able to work longer with uncleaned dirty shirts and the like. And this is all due to the fact that the CPAM pulls in the MOST amount of cable on one gear and, accordingly, the line error becomes less noticeable at the moment of switching, and the error affects the quality of switching in the least way.

And the conclusion at number two. the 10-speed SHIMANA pleased me, since the amount of pulled cable per transmission has significantly increased in comparison with the 9-speed transmission. Hence the reduction in noise in relation to the signal. HURRAH. This is the reason why the 10-speed SHIMANA began to work more “distinctly” than the 9-speed model, despite the increase in the number of stars and the decrease in the distance between them.

The perplexed townsfolk shrug their shoulders and nervously mutter, because, in theory, it should have happened that the transmission would be even worse than a nine-speed one. but no. everything is exactly the opposite you would still learn how to make switches without backlash.


Actually, it never occurred to me to write such an article initially, however, recent events simply do not leave any choice, and it rains outside, so you can sit on the couch at home, drink beer, surf the forums. but let’s start from the very beginning.

It was decided to dismantle the rear SHIMANO SLX 9speed transmission (shifters, rear shifter, chains, cassette) and purchase a 10-speed XT transmission. cassette 11-36, coins, shifter. The main reason for changing the transmission was the desire to change the 36 rear sprocket, and somehow it became boring, but, as they say, when your life stops bubbling, you need to change either the razor or the woman. Having carefully examined all the pros and cons, a decision was made to measure the transmission, because both the razor and the woman suited me. )))

In general, the updated transmission was glued together by the fins. the cock broke (at the same time, having fulfilled its function. preserving the frame dropout), but the rear derailleur ground and the frame turned out, so that the alignment of the rollers in the derailleur foot was disrupted and, to top it all off, the parallelogram of the frame floated. In short, the death of a career at its very rise. In the photo. life in the switch is slowly fading away, and the pulse has not died down yet:

In general, it was necessary to replace the switch, but the initial slackness inherent in the XT switches from the box jarred the brains, and SLH did not want it either, due to the fact that it uses a huge variety of “iron casting”, while it looked askance at the XTP his wife said that she would knock out a relative from the house only in contacts, and the HTR switch would stick out of the house…. Simply put, it was necessary to come up with a solution.

Here I read a great thread about the discussion of the decimal place, the essence of which was that our friend from Melitopol, Valera (XTR-ych), measured the cable samples for various rear transmission systems, and for this he thanks a lot, because the person did not regret your free time, and that is it, friends, is the only human resource that cannot be returned. thank you.


  • 1. Accurate operation of the transmission. We recall that the 10-speed SHIMANA pulls the cable almost the same amount as the 9-speed CPAM, which is MUCH more in comparison with the 9-speed CPAM, and, accordingly, the clarity of work increases.
  • 2. The switches of the 9-speed CPAM X9 (both 2010 and 2009. they have different rollers, if you remember) EXCELLENTLY cope with the task of throwing a chain on a star of 36 teeth !! HURRAH.

Indeed, the world is going crazy, the clearest 10-speed transmission will be obtained (with other factors being equal), if you use the rear 9-speed CPAM switch and SHIMANO coins for 10 gears. Regarding the issue of chains and cassettes. here it is optional, this post is not discussed.

Front derailleur

The front derailleur for a bicycle is the simpler of the two, but surprisingly a little more rare. There is a whole class of models (old sports and tourist, pleasure and cruisers) that do not use this element. This is usually done in order to simplify the design or reduce the cost of the bike.

Usually a device consists of several elements:

  • switch frame. the main element that works when switching, a circuit passes through it;
  • parallelogram mechanism. a set of joints that allows the frame to move in space without deviating from the vertical axis of the transmission;
  • fastening to the frame.
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The principle of operation of the rear derailleur

The rear derailleur is a parallelogram mechanism with a powerful spring that moves a frame (“foot”) with fixed rollers along the axis of the cassette. The speed selector is mounted on the 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 means of tension 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 switch parts.

Mounting on the hub axle

There are rear derailleurs that are attached to the hub axle, as opposed to conventional derailleurs that are mounted on the cock. This mounting method is used in extreme disciplines, given the reinforced construction of the equipment, they are more resistant to impacts that would cause a cock break on a regular bike. The disadvantage of such switches can be called a large weight, as well as the fact that if such a switch breaks down, you will often have to change the sleeve.

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.

What is the bottom line?

Each area of ​​application has a corresponding group of communicators. This is how the best mountain bike derailleur is cleverly defined.

  • For leisurely walks in the park area, Shimano Altus / SRAM X3 will be hassle-free.
  • Operation in a sparing amateur mode 50%. dense soils / 50%. asphalt will be moderately unpretentious in case of installation of Shimano Acera / CPAM X4 dealers.
  • Shimano Alivio / SRAM X5 are prescribed for cycling and advanced riders for training on medium terrain. Such a speed switch on a bicycle practically does not need repairs or readjustments.
  • Shimano Deor / CPAM X7 are recommended for those who like to train on a difficult “intersection”. Often find their application in cycling.
  • Selectors from the Shimano SLX / XT / XTR-SRAM X7 / X0 ranges are recommended for pro athletes in challenging off-road driving.
  • SRAM XX is the best equipment in the world. For use on bikes preparing for world-class competition.


The bike’s rear derailleurs have two plastic rollers: a guide (top) and a tensioner (bottom). On some rear derailleur models, these rollers are not interchangeable. 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.

Differences between bike rear derailleurs

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

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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.

Shimano Altus

Neither fish nor fowl. The most controversial line of switches in my opinion. In terms of speed and shifting accuracy, they are not much better than the Tourney, 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 ride infrequently, for a short time and not far.

Pros: low price, acceptable durability.

Cons: low accuracy and low reliability, the chain still jumps over the sprockets from shaking and hits the lower frame.

In the road range corresponds to the Shimano 2300 group.

Rear derailleur designs

Rear gearshifts are high and wear out periodically. When the question arises of replacing the derailer, one must not be mistaken with the choice. All switches are classified according to these criteria.

How to choose a rear derailleur for a bike

Is it necessary to generalize something here? In my opinion, no. The choice of the switch is an individual matter for everyone, depending on the needs and financial capabilities. Don’t forget to check out SRAM’s line of derailleurs. Shimano’s main competitor.

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Thank you for your attention, Alexey Evdokimov


Rear sprocket set. Mountain bikes typically have sprockets between 11 and 34. The number of teeth on the system relative to the teeth on the cassette is called the “gear ratio”. On a modern bicycle, the number of cassette stars ranges from 6 to 10. A larger number of stars gives a significant increase in the possible gear ratios with the cassette, which allows you to choose a comfortable gear for any road slope and this allows you to drive on a very steep slope.

Front hub

Secures the front wheel and provides rotation.

Seat clamp

Clamps the seat post into the frame. Available with an eccentric or a regular bolt (cheap models).

Feature of operation of the rear derailleur

In order for the bicycle derailer to work stably and properly, it is important not only to set it up correctly, but also to observe certain storage rules. This is explained as follows. The increase in speed is due to the tension in the spring in the derailleur, and the decrease is due to the release. Over time, it becomes not as elastic as initially. This is partly because when you leave your bike for long-term storage in the winter, you forget that you are in high gear. To avoid weakening the spring, before placing the bike for storage, set the speed at which its tension will be minimal. In this case, both the spring and the switch itself will last much longer.

Another common problem is dirt on bike rollers. They need to be cleaned as necessary and especially watch for wear. A sign that the rollers need to be changed is the sharpening of the teeth. New bike rollers have flat tips. It is not superfluous to clean the mechanism itself, since it is constantly in contact with dirt. Change the derailleur cables from time to time, about twice a year. This work is not easy, requiring a certain skill, so it is better to use the services of a master. Compliance with these rules contributes to the fact that your “horse” will serve a long and stable.

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.

Protection methods

  • Using the Shadow technology. This technology has been patented by Shimano. The peculiarities of the placement of derailers are such that when the bike falls, both they and the adapters suffer much less;
  • Protective frames. This is a steel device that attaches to the bike frame and covers the derailleur. At the same time, there is a greater chance of remaining unharmed when falling and the adapter.


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

As a rule, they are made of plastic. Since they are significantly erased, they require periodic replacement. With the wear of the rollers of the bike, the quality of gear changes deteriorates. Idler and idler rollers are not interchangeable parts of the unit. In addition, the rollers from different bike companies are also not compatible.

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 bike frame or through an adapter called a “rooster”. The advantage of such a device is that when dropped, neither the switch nor the axis is damaged, but only the adapter. Naturally, repairs will be much cheaper than in the previous version.

Gear ratio

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

Therefore, bike transfers from these companies are not interchangeable. At the same time, the clarity of gear shifting is approximately the same.

How to choose the right rear derailleur

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

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 no significant advantages in reverse switching, therefore such products are not very popular.