Derailleur gears
（重定向自Front derailleur）
![Shimano 600 front derailleur (1980)](/Images/godic/202501/14/14-06-20-shimano-600-RalfR-N3S_7903-052517.jpg")
![A modern road bicycle drivetrain with front and rear derailleurs](/Images/godic/202501/14/Derailleur_Bicycle_Drivetrain.svg2518.png")
![Campagnolo Super Record rear derailleur (1983)](/Images/godic/202501/14/Campagnolo_Super_Record_rear_derailleur_19832518.jpg")
![Shimano XT rear derailleur on a mountain bike](/Images/godic/202501/14/Shimano_xt_rear_derailleur2518.jpg")
Derailleur gears are a variable-ratio transmission system commonly used on bicycles, consisting of a chain, multiple sprockets of different sizes, and a mechanism to move the chain from one sprocket to another. Although referred to as gears in the bike world, these bicycle gears are technically sprockets since they drive or are driven by a chain, and are not driven by one another.