Derailleur

 

Derailleurs are the mechanisms that transfer the chain between sprockets. The mechanism near the back wheel is the rear derailleur. The one near the pedals is the front derailleur.

The derailleur system is the standard gear shifting system on road bikes and mountain bikes.

Sometimes misspelt ‘derailler’.

Shimano 300EX rear derailleur

A Shimano rear derailleur

A Shimano front derailleur

A Shimano front derailleur