Derailleur

This article is about the gearing system of a bicycle. For the railroad derailer, see Derail. For the act of derailment itself, see Derailment.
Shimano 600 front derailleur (1980)

A derailleur (French pronunciation: [deʁajœʁ]) is a variable-ratio bicycle gearing system consisting of a chain, multiple sprockets of different sizes, and a mechanism to move the chain from one sprocket to another.[1]

Modern front and rear derailleurs typically consist of a moveable chain-guide that is operated remotely by a Bowden cable attached to a shifter mounted on the down tube, handlebar stem, or handlebar. When a rider operates the lever while pedalling, the change in cable tension moves the chain-guide from side to side, "derailing" the chain onto different sprockets.

  1. ^ Oxford English Dictionary (2nd ed.). 1989. derailleur, n. A bicycle gear in which the ratio is changed by switching the line of the chain (while pedalling) so that it jumps to a different sprocket on the rear wheel. Also derailleur gear.