Modern mountain bike parts must stand up to a whole heap of abuse and the rear derailleur is no exception. Not only do they have to deal with riders in Internet forums screaming for bikes with gearboxes rather than derailleurs, they also have to cope with some of the most testing conditions and expectations. MTB rear derailleurs must shift smoothly under load, even when covered in mud and grit, and all while being able to withstand some substantial knocks from trailside debris. With modern clutch-type derailleurs, they’re also expected to help keep your chain in place over rough ground as well.
Fair to say then, that MTB rear derailleurs take a lot of abuse but thankfully the wonder of trickle-down technology has meant that modern rear derailleurs are tough, capable of shifting smoothly and also represent great value. The constant evolution of bike components also means that the latest range is the highest standard ever made, so no matter what rear derailleur you need for your mountain bike, you can be sure it’s up to the task.