Cassettes / Cogs

The set of cogged wheels used by derailleur gears have been given a variety of names (cogset,cluster etc.) and are the set of multiple rear sprockets attached to the hub on the rear wheel. The set works with the rear derailleur as part of the drivetrain to provide multiple gear ratios for the rider. There are two varieties, cassettes or freewheels, of which cassettes are a newer development. Although cassettes and freewheels perform the same function and look almost the same when installed, they have important mechanical differences and are not interchangeable. The terms are sometimes incorrectly used interchangeably. Most modern bikes now only use Cassettes.