derailleur

American  

[dih-rey-ler] / dɪˈreɪ lər /

noun

1. a gear-shifting mechanism on a bicycle that shifts the drive chain from one sprocket wheel to another.

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derailleur British  

/ dəˈreɪljə /

noun

1. a mechanism for changing gear on bicycles, consisting of a device that lifts the driving chain from one sprocket wheel to another of different size

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Etymology

Origin of derailleur

1945–50; < French dérailleur literally, a device causing disengagement or derailing, equivalent to déraill ( er ) to derail + -eur -eur

Explanation

The part of your bicycle consisting of a chain that moves from one toothed wheel to another when you shift gears is called a derailleur. The French dérailleur, first used around 1930, was inspired by the way a train derails from its tracks, the wheels slipping off to one side. On a bike, this happens on purpose, part of the process of shifting from one gear into another: The chain "derails" off one sprocket and onto another. Before the invention of this device, cyclists had to change their wheels in order to climb steep hills. Most modern bicycles have two derailleurs, in front and back.

Example Sentences

A single derailleur cable found snapped in two during a bike ride I took in Italy morphed into something more sinister.

From Washington Post • Aug. 12, 2022

Grid View The Gates carbon belt drive, which is quickly becoming a popular choice among bike manufacturers, is a cleaner alternative to the derailleur and chain ring and requires less maintenance.

From The Verge • Aug. 19, 2021

“They need to figure out how to deal with the easy repairs, flat repair, adjusting the derailleur and changing the chain.”

From Seattle Times • Apr. 21, 2021

Romain Bardet, the AG2R rider who won Thursday’s stage, developed a problem with his front derailleur and repeatedly kicked it with his heel and prodded it with his hand.

From New York Times • Jul. 24, 2015

The following afternoon, the policeman pounded the wheel back into shape, fixed the derailleur, replaced spokes, and bolted steel bars over the aluminum which attached the trailer to the bicycle.

From Take Me for a Ride: coming of age in a destructive cult by Laxer, Mark Eliot