How to choose a rear derailleur for your road bike, MTB, or hybrid bikes

Posted at: Jun. 11, 2021

How to choose a new rear derailleur for your road bike, MTB, or hybrid bikes, what to look for in a combination of sprockets, and the differences between different grades.

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How to choose a rear derailleur for any type of bike is the same

Whether you want to replace the rear derailleur on a road bike, MTB, or hybrid bikes, the basic procedure for selecting a rear derailleur is the same.

  1. compatible speed range (speed)
  2. it must match the sprocket capacity

These are the two most important factors.

If you keep these two points in mind, you will be able to use any bike.

Compatible gearshifts (speeds)

Rear derailleurs have a corresponding number of gears.

For example, if you have a Shimano rear derailleur, you can use an 11-speed rear derailleur for an 11-speed drivetrain, etc. The official position is that rear derailleurs can only be used in one supported speed range.

However, since the STI lever pulls the shift wire relatively close to the 8th to 10th gears, there are many reports on the internet that the rear derailleur can be used in these gears. However, since the rear derailleur combination is not recommended by the manufacturer, there is a possibility of gear shift malfunction.

Make sure the sprocket capacity is correct.

When replacing the rear derailleur, it is common to fail to check the sprocket capacity of the rear derailleur.

The rear derailleur has a sprocket capacity that is set by the manufacturer.

The sprocket capacity is determined by the number of teeth (denoted by T), and the main capacity indicators are the following three points

  1. low max/min
  2. high maximum/minimum
  3. total capacity

For different capacities, the corresponding rear derailleur is different.

In Shimano’s case, SS (short cage) is generally used when the low maximum is around 28T or 30T, and GS (middle cage) is used when the low maximum is around 30T or 32T. This differs from product to product, so be sure to check the sprocket capacity of the rear derailleur you plan to use on the manufacturer’s website beforehand.

For more information about the difference between SS and GS rear derailleurs, please refer to the following article.

Is there a difference in grade for the same number of steps?

The last thing you need to worry about when choosing a rear derailleur is the grade of the components.

For example, in terms of Shimano’s 11-speed components for road bikes, the following 6 rear derailleurs are compatible with 11-speed.

  1. DURA-ACE: rd-r9100, rd-9000
  2. ULTEGRA: RD-R8000, RD-6800
  3. 105: RD-R7000, RD-5800

All of them are officially announced by Shimano to be compatible, so you can use them in your 11-speed drivetrain.

I know that DURA-ACE is the best, but “If I only use DURA-ACE for the rear derailleur in 105, will it improve the shifting performance? Is there any difference between 105 and ULTEGRA? Are there any differences between 105 and ULTEGRA?

There is no doubt that a higher grade rear derailleur is better, but it is generally said that there is no difference that a layman can understand if the number of steps is the same.

The rear derailleur is a part that is not that expensive compared to the STI lever, so it is a good idea to start with a lower grade and upgrade to a higher grade.


We have seen how to choose a rear derailleur for a road bike, MTB, or hybrid bikes.

The rear derailleur is not difficult to customize once you understand how it works, but it is easy to buy the wrong product when replacing it by yourself.

The manufacturer’s website has detailed specifications, so make sure you check them carefully before purchasing.

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