Cassettes
A bicycle's rear sprockets (or cogs) must be removed and replaced when worn out. The rear sprockets can also be replaced in order to tweak the bicycle's gear ratio based on personal preference. Bicycle cassettes are designed to be mounted on the freehub body of the rear wheel's hub. Bicycle cassettes are removed and installed using a unique set of tools, so make sure you have the proper equipment if you're planning on replacing your bicycle cassette yourself. It's also important to double check compatibility between the bicycle cassette, shifter and chain.
