If the shifter is the instruction-giving brain of the drivetrain, the rear derailleur is the brawny laborer that gets the job done. With the SRAM X01 Eagle drivetrain, the 12-speed rear derailleur may be capable of great physical feats, all day long, it is more like the bionic version, with power and ability beyond that of mere mortal versions. Building on the single chainring drivetrain X-Horizon rear derailleur design, the X01 Eagle 12-Speed Rear Derailleur gets top materials and craftsmanship, with every aspect of the design engineered for the load and precision required to make Eagle soar, appearing silent and effortless despite the great range of the cassette and narrow dimensions of the 12-speed system. With it's upgraded Roller Bearing Clutch and Cage Lock, controlling chain action and swapping wheels have never been more enjoyable. The precise, positive shifts of the 1:1 ratio made possible by X-Actuation from the shifter through the derailleur have never been faster, over the greatest range every seen in a cassette. Top quality materials and construction ensure incredible shifting, durability and light weight. At 279 grams this Eagle specific design will not only turn heads, but leave you staring in awe from the pure performance.

The body and cage design of X-Horizon increases mechanical efficiency while resisting torsional forces that result when the unit is under serious pressure from shifting under load. SRAM redesigned the entire unit from the X01 11-speed model. The curves and angles reflect strength and extremely deep knowledge of how force loads must be managed. The forged aluminum is stout, yet sculpted strictly for what is necessary. There is no excess of material to make you feel better about the look. The new B-Bolt (Knuckle) mount design is a great example. At first glance it looks minimal, but when you examine it closely you see how the shapes and sectioning create strength, which makes this crucial zone stiffer and stronger than its predecessor, for great durability and consistency under load and aids in quieting the system. The cage is pure X-Horizon, optimized in length and stiffness for the staunch requirements of of Eagle's 10-52 cassette despite it'relatively compact length. The offset inner plate is machined and shaped from forged aluminum to resist wear, flex and torsion as the outer plate, which works in conjunction with the inner plate via the pulley wheels to keep the cage tracking perfectly inline with the intended shift.

SRAM has designed X-Sync pulley wheels that have optimal teeth profiles for the Eagle 12-speed chain. These hyper specific pulleys carry the chain smoothly, and have been paired specifically to manage the long chain required for the full cassette range. The re-positioned upper pulley has 12 teeth and the lower has 14 teeth, allowing the cage to be a moderate length. The pulleys travel on super smooth stainless steel bearings, which are durable, cost effective and easy to maintain. Managing the cage is a newly iterated Roller Bearing Clutch. This type-3 version was developed for Eagle, but we can see it filtering down, as it features a smoother torque curve, which makes the system quieter and performs more consistently as the derailleur is shifted. By preventing the cage from bouncing and the chain the slapping, the clutch system improves durability and safety, while keeping the derailleur perfectly postured for your next shift. The Cage Lock Button still allows you to lock out the derailleur cage position for easier, faster wheel changes, but the location has moved rearward of the Roller Bearing Clutch pivot, which keeps it somewhat sheltered from mud and dirt coming upward as you ride forward. Smart, and effective.

With Eagle, SRAM's shifting has never been smoother faster, or more precise. Refinements at the lever start the process, and this amazing X01 Eagle 12-Speed Rear Derailleur delivers, every time. The SRAM engineering team had already created excellent systems from which to build on and improve but you have to admit, the inspiration for Eagle challenged every physical and technical requirement. Shifting a 12-speed chain off a 1x crankset, over a 10-50 or 10-52 cassette? Until SRAM showed their hand, no one expected this. And the precision and ruthless effectiveness is truly astounding, especially over the wide range, crazy chainlines, on hardtails or full-suspension designs. Inspired, for sure, and mastered with advances that every SRAM mountain bike drivetrain will benefit from as the lessons learned are dispersed. For now, the only place to get a 1x12 drivetrain is with Eagle, and the X01 model saves weight and delivers impeccable performance.