The Complete Guide To Rear Derailleurs

Rear derailleurs, often referred to as ‘rear mechs,’ shift your chain across the different sprockets in your cassette to achieve higher or lower gears. They are spring-loaded to take up slack in the chain, improving shifting efficiency and helping you spin faster and get more power out of each pedal stroke!

The rear derailleur, or rear mech, is a crucial component of any bike with more than one sprocket in the back. It facilitates shifting between these sprockets, helping you spin up hills with ease and putting some power down on flats. The cage of a rear mech holds two pulleys — the idler wheel and the jockey wheel — that run around your chain. These pulleys keep the chain in a light tension, which allows your rear mech to shift gears. A longer cage will take up slack in your chain from larger gears, while a shorter one will work best with smaller ones. Ultimately, this means you’ll need to choose the right derailleur for your ride. 

The derailleur comes in several designs, depending on the type of bike you ride. Some are designed for rougher terrain while others are more efficient and easier to adjust. Some derailleurs have a larger cage size, which means they can handle bigger sprockets. This is especially helpful for mountain bikes that see a lot of action on rough trails and bike paths, where smooth shifting while pedaling hard is critical. For example, if you’re running a cassette with a 50-tooth bottom sprocket and an 80-tooth top sprocket, then you’ll need to look for a derailleur with at least 39t capacity. 

Rear derailleurs are often considered to be more finicky than their internal-gear-hub counterparts, and dirt, grime, and water can quickly wear them down. So, it’s important to perform occasional maintenance on your rear derailleur. The right maintenance can keep your system working at peak performance and make sure you’re able to cover more ground on the bike with less effort. 

And while it’s true that you can get derailleurs that are more durable than cheaper alternatives, there’s also a big difference between them. Typically, the higher-end options use harder-wearing materials like carbon cages and titanium pivots. You can even find a few that spin on cartridge bearings instead of standard steel bushings. These components tend to last a lot longer than their cheaper counterparts, so it’s worth spending a little extra if you want to avoid the need for frequent maintenance visits. 

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