MTB Rear Derailleurs

MTB rear derailleur

The MTB rear derailleur, sold alone or as part of a complete MTB groupset, is used to move the chain between the different sprockets on the cassette to change gears.

The derailleur is attached to the frame and is one of the most exposed parts of the bike. In order to avoid damage to the frame in the event of a fall (or mistreatment) of the bike, it is attached to the frame with a derailleur hanger. This part therefore acts as a fuse and it is this part that bends or breaks if the load is too strong. The derailleur consists of a clevis, 2 rollers and a complex assembly of springs and other mechanical parts.

A shifter is used to operate it. There are 3 main types of gear shifters:

Frame-mounted shifters (this type of shifter is now outdated and no longer offered for sale),
Turning levers,
Handlebar shifters

Shimano derailleur or SRAM derailleur

There are currently only two manufacturers who share the entire MTB derailleur market: Shimano and Sram.

Which rear derailleur clevis to choose?

The derailleur clevis is used to tension the chain and dampen chain movements when shifting gears.
When replacing a mountain bike derailleur, we advise you to use the same chain length.
For a custom assembly or a development modification, the only way to avoid mistakes is to calculate the "total capacity" of the derailleur: "Total capacity= (Number of large sprocket teeth - Number of small sprocket teeth) + (Number of large gear teeth - Number of small gear teeth)"

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The bike derailleur: an essential part of the bicycle transmission

A derailleur is the mechanism for changing gears on a bike. It consists of a front derailleur that changes the chainring and a rear derailleur that moves the chain on the sprockets. The cyclist changes gears using a lever on the handlebars.

To calculate the gears of a bike, simply multiply the number of chainrings on the crankset by the number of sprockets on the rear hub. For example, if the bike has 3 chainrings and 7 sprockets, there are 21 gears.

The bike derailleur must allow you to change gears quickly and accurately.

Shimano Derailleur

It is a central part of the drive train.

The Shimano derailleur is used on many bikes and mountain bikes and is available in different groups: Deore, XT or XTR.

The materials generally used to manufacture derailleurs: steel, aluminium, carbon, titanium.

The front and rear derailleur should be cleaned regularly to facilitate shifting and prevent wear.

Sram derailleur

Sram is Shimano's competitor in the field of mountain bike drivetrains. The American company offers numerous models of derailleurs for bikes.

The materials that make up the derailleurs: steel, aluminium, carbon, magnesium, titanium that offer performance and resistance.

Make sure that the clevis size is compatible with the capacity of the SRAM cassette. If the total capacity (number of teeth) is too large for the size of the clevis, the chain will be too taut and may break.

Maintenance of the rear derailleur is important and should be cleaned regularly. The rollers should be clean but do not need to be greased and should be replaced when worn.