derailer

A derailer, also commonly spelled derailleur, is a mechanical device used in bicycle gear shifting systems to move the chain between different sprockets on a cassette or freewheel, enabling the rider to select different gear ratios. Derailers are typically situated near the rear wheel and are assisted by shifter mechanisms operated via cables, which guide the derailleur to position the chain appropriately.

There are two primary types of derailers: rear derailleurs and front derailleurs. Rear derailleurs control the movement across multiple sprockets, allowing for a wide range of gear ratios, while front derailleurs manage the chain's position on chainrings at the crankset. Both types work together to provide a broad spectrum of gears suitable for various terrains and riding styles.

The design of a derailleur includes components such as a cage or pulleys that guide the chain, a spring mechanism that maintains tension, and mounting hardware for attachment to the bike frame. Modern derailers often incorporate features like indexed shifting for precise gear changes and are constructed from materials such as aluminum or carbon fiber for strength and weight savings.

Derailleurs have evolved significantly since their early use, with technological advancements improving shifting performance, durability, and ease of maintenance. They remain a popular choice for many cyclists, particularly those engaged in road racing, mountain biking, and touring, although hub gears and belt drives are alternative shifting systems.

Proper adjustment and maintenance of derailers are crucial for smooth operation and to prevent chain drops or excessive wear. They play a vital role in enhancing cycling efficiency and rider comfort by facilitating seamless gear changes across varying terrains.