Cage, in the context of a bike refers to components on front and rear derailleurs that manipulate the chain when gears are changed. On a front derailleur, a cage is composed of two pieces of metal that shift the chain from one chainring to another. On a rear derailleur, a cage consists of two wheels and serves the function of shifting the chain across the cassette as well as tautening the chain.
Endurance cycling requires effective gear shifting. The smoother-working cage facilitates gear shifting, allowing riders to maintain an even speed when riding on various terrains. The rear derailleurs have cages of varying lengths: short, medium, or long, depending on the gears of the bicycle.
