A rear derailleur is an electronic or mechanical drivetrain component that is mounted on the bike frame and is responsible for moving the chain from one gear to another on the rear cassette of the bike.
The rear derailleur is controlled by a shifter, which is typically located on the handlebar of the bike. When the rider wants to change gears, they use the shifter to move the derailleur, which in turn moves the chain to the corresponding gear on the rear cassette. Rear derailleurs come in different sizes and designs, but they all work in the same basic way.
What Makes up a Rear Derailleur
The rear derailleur is composed of several key components, including the derailleur cage, the jockey wheel, and the derailleur hanger. The derailleur cage is the main body of the derailleur and is responsible for guiding the chain from one gear to another. The jockey wheel is the small wheel that is located at the bottom of the derailleur cage and is responsible for keeping the chain in place. The derailleur hanger is the part of the derailleur that attaches it to the bike frame.
One of the most important features of the rear derailleur is its ability to adjust the distance between the jockey wheel and the rear cassette. This is known as the derailleur's "limit screws." These limit screws are used to set the maximum and minimum distance between the jockey wheel and the rear cassette, which helps to ensure that the chain cannot fall off the gears.
Another important feature of the rear derailleur is its ability to adjust the tension of the chain. This is done by adjusting the barrel adjuster, which is typically located on the derailleur itself. By adjusting the tension of the chain, the rider can ensure that the chain is tight enough to engage the gears properly but not so tight that it causes the gears to wear out prematurely.
Short Cage vs Long Cage Rear Derailleurs
Rear derailleurs also come in different designs, including short-cage and long-cage. Short-cage derailleurs are designed for use with bikes with fewer gears, while long-cage derailleurs are designed for use with bikes with more gears. The number of gears on a bike is determined by the number of cogs on the rear cassette, and the size of the rear derailleur must match the number of cogs on the rear cassette for the bike to shift properly.
