SRAM refers to the XX1 Eagle rear derailleur as the brain of the system. Trimming it at setup eliminates chain rub for a nearly silent operation. This simultaneously improves the longevity of the drivetrain. This version is compatible with 10-52t cassettes but is backwards compatible to accommodate 10-50t. With this derailleur, you will feel instantaneous changes in your mechanical system as you engage the derailleur. It works just as smoothly regardless of how fast you are moving. Cross country riders are always looking for the smallest edges to help them go faster and the new SRAM XX1 Eagle Rear Derailleur with an improved gear range is a great way to pick up speed.