Derailleur SummaryDérailleurs consist of a chain, multiple
sprockets and a mechanism to move the chain from one
sprocket to another.
Modern front and rear dérailleurs typically consist of a movable chain-guide that is operated remotely by a Bowden cable attached to a shift lever mounted on the
down tube, handlebar stem, or
handlebar. When a rider operates the lever while pedaling, the change in cable tension moves the chain-guide from side to side, "derailing" the chain onto different
sprockets. To both guide the chain to the selected
sprocket and maintain chain tension by taking up any slack caused by changing to a smaller
sprocket, the rear dérailleur has two
pulleys in a spring-loaded rotating cage, through which the chain rolls in an S-shaped pattern. The
pulleys are known as the guide
pulley (top) and the tension
pulley (bottom). Together they are commonly referred to as the jockey
pulleys or
wheels. The front dérailleur has a cage that should touch the chain only while
shifting between the front
chainrings.Full Article
