Single-speed bicycle builders have converted many former multi-geared cycles into single or fixed speed through the removal of the derailleurs and associated hardware. The simplest conversion uses the existing freewheel/cassette and crankset, the chain being cut to fit the desired gear ratio. However this retains unnecessary weight and the chainline will most likely not be perfect. A more thorough conversion will involve replacing the freewheel with a single-speed one, and re-dishing the rear wheel. On bicycles with vertical dropouts, a chain tensioner is often required to allow the correct tension on the resulting shorter chain.