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Everything you need to know about the rear derailleur of a bicycle
A derailleur is a bicycle part that allows the movement of the chain on the sprockets or chainrings to change speed, therefore development, par demultiplication or multiplication. The word derailleur used in cycling appears in 1927 to designate the device allowing you to change gears on a bicycle.
The rear derailleur moves the chain to the selected sprocket. It includes a chain tensioning system, responsible for adapting its length to the diameter of the chosen sprocket. The front derailleur is responsible for changing the chainring to adopt the most suitable gear.
How to choose your rear derailleur according to your practice, without forgetting to give you technical and practical details.
To find out more about bicycle transmission, follow our advice You can consult it by clicking here..
Rear derailleur operation
Essential on a speed bike, the rear derailleur is a mechanism made up of a spring and rollers allowing you to change gears. A cyclist needs to change gears when the elevation also changes. The derailleur allows you to modify the development of the transmission, that is to say the number of meters covered with each revolution of the pedal.
Attached to the bicycle frame, it moves laterally to guide the chain. It is connected to the derailleur lever par a cable.
The rear derailleur has two functions: changing gears and keeping the chain tensioned. A movement of the derailleur lever activates the cable, which in turn causes the derailleur to move so that the chain moves onto another sprocket. It is thanks to a spring that the chain remains taut regardless of the sprocket used.
The adjustment of the rear derailleur must be very precise for proper operation of the bicycle transmission and to avoid derailing.
What are the selection criteria?
Compatibility
The number of speeds (1):
Indexed rear derailleurs (the most common today) are designed for a defined number of gears. Your deception can be developed for a transmission of xnumx, xnumx, xnumx, xnumx, xnumx, xnumx, xnumx, xnumx speed or more).
The rear derailleur should always match the number of speeds on your cassette or freewheel. Par example: equip yourself with a 7-speed derailleur for a 7-speed cassette. Do not mount a 9-speed derailleur with a 7-speed cassette: indexing would not work.
Clevis length (2):
The cage length of your rear derailleur must be compatible with the number of chainrings. There are three cage lengths in the rear derailleur world.
• Short screed: A short cage rear derailleur is lightweight, less exposed to shocks (car the yoke is shorter) and gives the possibility of reducing the chain length. But it does not allow all combinations between chainrings and sprockets! It is generally mounted on single chainring bikes.
• Average screed: intermediate cage which is generally suitable for double or triple chainring bikes. On a road bike or mountain bike and in sports use in particular, we are looking for minimum weight and maximum robustness.
• Long screed: A long cage derailleur is suitable for a larger number of sprockets and for a larger difference between the chainrings. Why this difference? The cage is longer, therefore the chain is longer. It will be able to reach the largest sprocket and the largest chainring without any problem.
What is the risk of a derailleur cage that is too short? The chain may be too tight when you are on the large sprocket and the large chainring. The gears may have difficulty shifting, and the risk of breakage is significant.
Pebbles (3):
Small wheels allowing the chain to move, the rollers guide it during gear changes. Often neglectedar cyclists, the rollers are very important for good gear shifting.
Derailleur pulleys are often made of polyoxymethylene plastic: they are relatively silent and resistant to the passage of the chain. There are also aluminum models. Warning: on a rear derailleur, we differentiate between the tension roller (lower roller) and the guide roller (upper roller)!
Like other elements of the transmission (chain, cassette, etc.), the derailleur pulleys must be replaced regularly depending on use: approximately every 10 kilometers. . A roller is worn when its teeth are pointed or rounded or when it has lateral play. A roller can also wear out in thickness.
The consequences of worn and poor condition rollers:
• Poor fit of the teeth into the chain
• Noise
• Loss of precision in transmission
Good to know: It is necessary to mount the rollers identical to the original rollers in the event of replacement, each derailleur using its own rollers. Don't have fun making original combinations.
Pay attention to the direction of rotation of the rollers during assembly!
The derailleur hanger (4):
The derailleur hanger is a intermediate between the frame and the derailleur. From par its aluminum design, it functions as a kind of fuse. It is she who breaks in the event of a fall or impact. to avoid damaging or bending the derailleur. A derailleur hanger is inexpensive to purchase and is easily replaced. Better to change a derailleur hanger than a rear derailleur, right? Par However, it must always be aligned with the axis of the bike.
Be careful, there are hundreds of different legs. Each has a specific shape adapting to the frame of the bike. Models are rarely interchangeable.
Check out our guide: Everything you need to know about the derailleur hanger.
The different types of derailleur
The non-indexed derailleur (friction system)
The non-indexed derailleur with a friction system is the most commonly used type of rear derailleur until the early 90s, accompanied by a lever on the frame or handlebars. Simply rotate the lever to pull the cable and change gears.
With this type of derailleur, it is up to the cyclist to operate by feeling their way, until the speed shifts. There is no notch in the controller. It's not always easy to find the right position with a non-indexed derailleur!
The indexed derailleur
The indexed derailleur appeared in the 80s. Innovation par compared to the friction system? Indexing, that is to say a system of notches on the controller. Each notch corresponds to a pinion. The speeds can thus be numbered on the derailleur lever.
For good indexing, the entire transmission must be of the same brand in order to have the same characteristics.
The integrated gear hub
The gear system integrated into the hub is a special case: nothing to do with a rear derailleur. Indeed, the gear switch is done through a gear mechanism integrated inside the rear wheel hub. This means you can have between 3 and 11 speeds, but only one cog and no derailleur.
The electronically controlled derailleur
Rshe technological advancement for competitive cycling, lThe gear change is no longer carried outar cable: the transmission management is electronic. These are electric motors which generate the movements of the derailleurs.
How to recognize the type of derailleur on a bike?
If your derailleur breaks, you must find an identical (or compatible) model to replace it.
Recognizing the type of derailleur on your bike is not always easy. You just need to ask yourself the right questions to recognize the type of derailleur on your bike:
Are you equipped with a rear derailleur and derailleur shifter?
-If controller, but no derailleur => integrated gear hub
-If lever and derailleur => classic derailleur
Does your derailleur lever have numbers or detents?
-If numbers or notches => indexed derailleur
-If no notches or numbers => non-indexed derailleur (friction system)
How many sprockets does your bike have?
This information is essential when choosing a derailleur.
What is the brand of your derailleur?
This information is very important to find a derailleur model compatible with your transmission.
What is the cage length of your derailleur? Refer to the paragraph above.
What brands? Three flagship brands govern the bicycle transmission sector: Shimano, SRAM and Campagnolo. Each manufacturer has its own mode of operation. Thus, a Shimano derailleur cannot be replaced par a SRAM component, not compatible with the rest of the transmission, and vice versa. So be sure to check the standard of the product before purchasing.
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