What are derailleurs?
Derailleurs are variable-ratio transmissions. The transmission system includes, but is not limited to, a chain, sprockets, and a mechanism(derailleur) to move the chain to different sprockets. Derailleurs often attach to the front or rear wheel on a bicycle.
Why are derailleurs important?
If you have a shifting bike, you have a derailleur. Without the derailleur, you could not shift. The derailleur moves the chain on the bike to the desired gear of the rider. It can also keep the chain from getting tangled and loose. The derailleur also provides some protection to the rear cassette and chain from collecting dirt or other debris.
How do derailleurs work on a bike?
Derailleurs attach to the front or rear wheel to provide shift-ability of the gears. A movable chain guide is attached to the derailleur. This chain guide is operated by a Bowden cable that is connected to a shifting device. The derailleur picks up the chain and moves it to the gear of which the rider is seeking. The derailleur also makes it so that the chain does not loosen and give slack, keeps chain tight. Most commonly, the derailleur does not shift unless you are pedaling.
How do you choose the right derailleurs for your bike?
Derailleurs, like all bicycle parts, come in many different shapes and sizes. There are two most common derailleurs that are used. These are the front wheel derailleurs and rear wheel derailleurs. The rear wheel derailleur has to perform two tasks for the rider while a front wheel derailleur only has to perform one. The rear wheel derailleur shifts for the rider and also keeps the chain tight. The front derailleur only has to do the shifting. Riders most often get a rear wheel derailleur. If you are looking for specific performance, it is recommended to check out the cage lengths. Keep in mind, having a shorter cage length can yield many benefits. Some of these benefits include, but are not limited to, positive gear changing, less weight, less chance of tangling in spokes, better gear changing, and good cable leverage.
Cage Lengths (length between upper and lower pulleys):
Shimano long: 45T
SRAM long: 43T
– medium : 37T
– short: 30T