How to choose your road bike rear derailleur?

Much more difficult than it seems, the choice of derailleur is fairly well defined — here is how to avoid making a mistake.

Standards

SHIMANO, SRAM or CAMPAGNOLO type
The number of speeds, today: 9, 10, 11 or 12
Cage length: short or medium

Choosing your cage length

Reminder: for the rear derailleur, SHIMANO, SRAM and CAMPAGNOLO do not all operate under the same cable pull standard, so you will not be able to mix these 3 brands.

As all the components of a drivetrain are designed to work under a specific speed standard, it is not possible to pair a 10-speed derailleur with an 11-speed drivetrain, for example.

For SHIMANO and CAMPAGNOLO, the length is determined by the capacity*, calculated as follows: (Maximum cassette sprocket – Minimum cassette sprocket) + (Maximum chainring – Minimum chainring). For example, with an 11/28 cassette and a 34/50 crankset, you would calculate (28-11)+(50-34) = 33. You will therefore need a derailleur with a capacity of 33.

Please note that the large sprocket must not exceed the maximum number of teeth accepted by the derailleur (for example 30 teeth).

The greater the difference in teeth between the smallest and largest sprocket, the more advisable it is to choose a medium-cage derailleur.

For SRAM, you must consult the brand's compatibility chart.

Simply make sure you choose a derailleur compatible with your gear shifters and fitted with a cage suited to your drivetrain.

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