When it comes to the SRAM Eagle 1x12 drivetrain, the rear derailleur is easily the most complicated constantly working component on the market. Built specifically to handle the full 11-50 cassette range, with the added complications of wider frames and hubs, as well as the single ring crankset, a component such as the NX Eagle 12 Speed Rear Derailleur is truly amazing, and to be fully appreciated, especially at the price point that NX Eagle offers.

For SRAM, the proven base of their shifting system is a 1:1 ratio as delivered by their X-Actuation system. Essentially the amount of cable pulled mechanically is exactly the amount required to index the shift. Other drivetrain systems have a more complicated ratio and leverage system, but SRAM riders love the ruthless efficiency and mechanical precision that is true across SRAM's mountain drivetrains. Concurrently for Eagle, SRAM uses X-Horizon technology to handle the range and loads. The X-Horizon rear derailleur's "straight parallelogram" design limits all movement to the horizontal axis, which makes ghost shifting impossible while also reducing shift force. For quicker, more exact shifting, the large upper pulley offset design maintains a constant chain gap across all gears.

The Eagle ecosystem-engineered mounting is carried across the full range, as is the Cage Lock system. By pushing the derailleur cage forward, it locks into an open position for a much easier path for wheel installation which is crucial with such a long cage, large cassette and the added challenges of thru-axle systems. SRAM was the driver of clutch technology for rear derailleurs, which is a real requirement for consistent chain engagement on 1x drivetrains. For the NX Eagle rear derailleur, the sleek and wholly effective Type-3 Roller Bearing Clutch™ provides quiet, consistent performance and durability. Finally the pulley wheels are engineered strictly for Eagle use. The wheel designs are specific upper and lower, and SRAM adds their X-Sync tooth design for the 14T lower pulley wheel, which manages the chain with a smooth fluidity that helps to keep the system running cleanly and as quietly as possible.