Front and rear derailleurs - also known as ‘mechs’ - enable you to move up and down the range of gears to suit the demands of terrain, speed etc. Mountain bike derailleurs are made to work in all conditions, including mud, rain and grit, and need to be robust enough to take a knock or two from trees and rocks. Road bike mechs don’t have to face up to quite the same conditions, but are nevertheless designed to work smoothly under pressure, while being light and functional.
