Shimano FD-M9025-H XTR Double Front Derailleur - Conventional Swing - Top Pull

What are derailleurs and mechs?

Derailleurs and mechs are two names for the same thing – the parts of your drive train that move the chain between chainrings for the front derailleur/mech and between the cassette cogs for the rear derailleur/mech.

Who needs a derailleur or mech?

Not all bikes have derailleurs, but if your bike has conventional gearing rather than singlespeed or hub gears, you will have at least a rear derailleur. These parts are exposed and somewhat vulnerable to damage, so you may need to replace them if this happens.

What are the choices?

Your choice will largely depend on what is compatible with the rest of your drivetrain, but there are different options for road and mountain bike, by the big three manufacturers, Shimano, SRAM and Campagnolo.

What should I buy with them?

If you’re replacing a front or rear mech, you may need to replace some other parts of your drivetrain as well, for compatibility or because you want them to wear together. These might include the chainrings, rear cassette or chain.

Anything else?

It’s not just compatibility with your other components you need to consider with a mech replacement. Derailleurs also have different fittings for various frame compatibilities, including braze-on fittings and a bolt-on collar.