Which statement best defines a derailleur?

• A. Gear-changing Device that allows a Rider to derail the chain and move it from one chain ring to another while in motion
• B. A braking device
• C. A chain
• D. A pedal crank

Answer: (A)

A derailleur is the bicycle’s gear-shifting mechanism that moves the chain from one gear to another while you’re riding. There are front and rear derailleurs: the front shifts the chain between chainrings, the rear shifts it across the sprockets on the cassette. This shifting changes the gear ratio, making pedaling easier on hills or faster on the flats. It’s not a braking device, not the chain itself, and not a pedal crank.