Bike Derailleurs

A bicycle derailleur is a key component of any bike’s drivetrain, allowing you to select the right gear ratio by changing the position of the chain on the sprockets.

Types of bicycle derailleurs

There are two main types of bicycle derailleurs: external and internal (planetary).

External derailleurs

External derailleurs are the most popular choice. They are simple in design and easy to service.

Internal derailleurs

Internal derailleurs are hidden in the rear wheel hub, which makes them more resistant to weather conditions and less prone to failure. The biggest disadvantages of planetary derailleurs are their greater weight and complicated servicing.

How to choose the right bicycle derailleur?

When choosing a bicycle derailleur, there are several things to consider, including the gear range, mounting method, intended use, and cage length.

Cage length

The length of the derailleur cage is the length of the derailleur arm that tensions the chain. The length of Shimano derailleurs can be identified by the markings “SS” (short cage), ‘GS’ (medium cage), and “SGS” (long cage).

• A short cage (SS) is suitable for road bikes with a small range of sprockets (e.g., 11-28T). It is lighter and more precise.
• Medium cage (GS) – most commonly used in trekking, city and cross bikes. They support a wider range of chainrings (e.g., 11-32T).
• Long cage (SGS) – used in MTB and trekking bikes with a large gear range (e.g., 11-42T).

Gear range

The key parameter when choosing a derailleur is the gear range (also called speed range).