Which rear derailleur to choose on a bike

Transmission: what are the best derailleurs on a mountain bike in various applications

The modern drivetrain layout, whether for road or mountain bikes, dates back to the mid-20th century. In the 1950s, the Italian Tullio Compagnolo invented a very convenient means of transferring the chain over the rear cassette sprockets. the rear derailer. Over time, the front.

Service and customization

Derailleurs are some of the most subtle elements of a bike to adjust. Minimal tolerances and the fatal effect of misalignment on the chain and sprockets. all of this dramatically increases the importance of correct tuning.

With the ride now standardized, cyclists have a little less set-up to worry about. Previously, it was also necessary to work with the tension of the cable. Now the main thing is to set the correct position of the extreme points of the switch.

This is done using bolts H (High, high position) and L (Low, low position). The chain is thrown first to the largest chainring in the front and the smallest at the back, and with constant observation, using the screw H, the bicycle derailleur is set so that the planes of the chainring, chain and derailleur frame become parallel. Then a similar adjustment is made for the other extreme stars using the bolt L.

There are many obstacles that can interfere with the simple setting of the switches, and which will require more serious intervention, which is already problematic to do it yourself:

  • damage to any frame;
  • discrepancy between the set of stars and the capacitance of the switch;
  • damage to the frame or cock;
  • cable drive mismatch.

It is best to avoid these issues before starting the setup.

What is the bottom line?

Each area of ‚Äč‚Äčapplication 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 difficult crossroads. They are often used in cycling tourism.
  • 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. Used on bikes preparing for world-class competition.

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).

How to choose a rear derailleur for your bike

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 tourism, 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.
  • The clamp on the frame is the simplest and most common. There is some risk of error in the diameter of the clamp, but this error can be easily corrected by replacing or additional spacers. There are several clamp mountings, with one, two and three attachment points. In addition, such fasteners may differ in the point of winding the cable into the mechanism.
  • E-Type is Shimano’s proposed and de facto standard bottom bracket mounting system. It is used on full-suspension and other bicycles with a complex configuration of frame tubes.
  • Bolt fastening to the frame is a rather rare, but very reliable fastening when a seat is already provided on the frame.
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Long Cage vs Short Cage Derailleurs. Which Do You Need

Construction and work

The principle of gear shifting is, in fact, very simple. Both devices are frames that, being controlled through a drive cable by a shifter (shift knob), shift their position relative to the stars on the system or rear hub, moving the bicycle chain with them.

At first glance, the trivial task is complicated by many factors:

  • heavy load on the transmission. modern front and rear derailleurs place high demands on materials;
  • positioning accuracy. small errors in the position of the frame (and, accordingly, the chain) can lead to rapid damage to the chain and stars by incorrect switching;
  • the subtlety of the mechanism. in a modern device there are more than two dozen elements, each of which must be almost ideally positioned and work under load.

Modern models are delicate mechanisms that require serious development and no less serious maintenance.

Let’s consider these devices in more detail. It should not be forgotten that both the rear and the front derailleur have their own restrictions on the types of attachment and the size of the allowed stars in the transmission. Rear frames are also limited in overall length.

which, rear, derailleur, choose, bike

Shimano Acera

In my opinion, this is the first line of switches that can be used on cycling trips. Naturally, they are not long and difficult, but these switches will already be pulled along the plain by the LDPE.

Pros: very average level, perfect balance between price, quality and accuracy.

Cons: the chain still hits the feather, although it practically does not jump on the stars from the shaking.

In the road range corresponds to the Shimano Claris group.

Cable feed

Switches are rarely divided according to the cable entry point, but it should be understood how the shirt will fit in the event of a device change.

The standard approach is from the back, when the cable in the shirt makes a circle around the dropout, forming a small loop. In this design, it is convenient to work with the cable, but the extra length of the cable and its bend lead to the need for more frequent maintenance and reduce the reliability.

SRAM derailleur with direct cable entry

An alternative is a straight line, where the cable enters the derailleur along the shortest path. Slightly more complicated handling of the cable and jacket is compensated by the greater reliability and security of the entire device. Originally only SRAM used this line, but in recent years Shimano and replica makers are increasingly switching to direct line.

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.

Rear Derailleur Type:

The rear derailleur on your bike plays a huge role in adjusting the chain length and tension. The derailleur foot moves back to maintain sufficient tension when you use the small chainring in the cassette, but it also compensates. However, it can also move forward when you switch to large stars to overcome the rise. Accordingly, the rear derailleurs are available in 3 possible versions: with short, medium and long foot / frame (depending on your preferences and the capabilities of the bike). The basic principle when choosing a new derailleur is that the wider the gear range, the longer the tab should be. If we consider the classic layout of a bicycle transmission with 3 stars in the system, then a long foot would be most appropriate there. If we are talking about models with one star in the system, then the short presser foot is fine. For example, if you want to use a short rear derailleur on a bike with a wide gear range, then you will also need to install a chain that is too long (which will compensate for the insufficient derailleur length). And, unfortunately, there is no golden mean here. An incorrectly sized rear derailleur will prevent you from finding the correct chain length and avoiding breakage.

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A chain that is too long will fly off often and cause shifting problems; too short can rip your rear derailleur off. You can’t wait to check the chain length on your bike?

Features of double suspensions

Setting the required chain length is not a difficult task, but everything becomes not so easy in the case of double suspensions. Why is this happening? Many bike manufacturers use suspension arrangements that improve pedaling efficiency. In this case, as the suspension is triggered, the distance between the carriage and the rear wheel axle increases. This displacement can occur throughout the entire suspension travel, or only within a certain range. But in any case, this means that a longer chain must be installed on a two-suspension, all other things being equal, than on a hardtail.

Squeeze the suspension all the way, because it is in this position that you will be able to determine the appropriate chain length. If your bike has an air rear shock absorber, simply bleed the air through the valve (it looks like a car nipple) while compressing the suspension with your weight. In the case of a spring-loaded shock absorber, you will have to first remove it from the frame, remove the spring, and then insert the shock absorber back.

Before you start to manipulate the shock, you need to shift the chain to the largest sprockets in the cassette and system. For convenience, you can fix the bike in a repair rack, if there is one.

If the chain length is too short, you will immediately notice it from the position of the rear derailleur foot. The photo above shows the rear derailleur position when the suspension is fully depressed. We can say with confidence that such a chain length at best causes a breakdown of the cock and the rear derailleur itself. Accordingly, you need to add several links, or choose a longer chain.

The photo above shows the position of the rear derailleur with the correct chain length. By adding just two additional links, we have saved ourselves from many potential problems.

Shift the chain to the smallest sprocket in the cassette and system. If you see a picture similar to the photo on the left, then the length of the chain is matched almost perfectly. We see that the chain is tight enough, but at the same time the necessary free play is preserved, and there is also a margin for switching to larger stars. The right photo shows a chain that is too long, which, as we have already found out, can lead to serious damage to your bike, as well as regular chain jumping off the stars.

The rear derailleur is not such a mysterious part of the bike as it might seem at first. A clear design and a simple mechanism allow us to conveniently use these devices for more than half a century. After reading this article, we hope it will be easier for you to choose a new derailleur or customize it yourself without involving the mechanics from the bike shop.

How a Rear Derailleur Works


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.

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

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.

Bicycle rear derailleur

Many bicycle lovers, while riding, gradually master the tuning and minor repairs of their bikes: here. tighten the brakes, there. change the saddle. But when it comes to the rear derailleur, a lot of people fail. Such a complex and not completely clear design raises more questions than answers, and portends difficulties not even in setting up, but in installing and removing.

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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, such as gravity: Down Hill, Free Ride, Dirt, etc. But do not be confused by the word inferior, 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.

Switch types

All bicycle derailleurs can be divided into two main types:

  • internal gear shifting mechanisms;
  • external gear shifting mechanisms;
  • combined mechanisms.

Which rear derailleur to choose on a bike

First of all, it will be useful to answer the question: “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 must 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 need to select the highest gear that will allow you to develop the 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 bicycle equipped with this type of derailleur, you will not see cassettes with sprockets of different sizes and with different numbers of teeth and hinged derailleurs. As a result, the wheel drive has only one sprocket in the front, a chain and one sprocket in 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 the planetary hub The structure of the 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 widely used on road and walking bikes, although sometimes they can also be found on mountain bikes.

  • resistance to adverse road and weather conditions, due to the fact that the switching mechanism is completely located in the housing;
  • built-in brake;
  • high reliability and durability;
  • the ability to shift gears without turning the pedals;
  • ease of maintenance.

However, planetary hubs also have significant disadvantages:

  • high weight;
  • strong friction of nodes, which complicates movement;
  • repairability in field conditions.

Front derailleur.

Its task is to transfer 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. over, 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 mount the switches on frames with non-standard geometries.
  • Installation angle in relation to 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 that 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 unable to transfer 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.