Shimano developed the Dura-Ace R9100 cable-actuated mechanical rear derailleur for road use but with direct engineering cues from XTR M9000. As the Japanese engineers designed the R8000 version, the same principles and improvements carried over, and your only "sacrifices" from Dura-Ace is about 40 grams, a few minor hardware changes and aluminum plates versus Carbon Fiber Reinforced Plastic. The decision was also made to make the 11-speed Ultegra RD-R8000 in both short and mid-cage versions so the design could provide efficiency and ultra-crisp shifting for smaller and larger range cassettes. The GS design can accommodate the new 11-34 CS-HG800 cassette. The R8000 rear derailleur were also optimized with the R8000 and R9100 dual control STI levers for faster, more positive shifting, with less hand effort, making the RD-R8000 a perfect "upgrade" with larger 32 and 34T cassettes for Dura-Ace.

The RD-R8000 adopts the same R9100 Shadow compact profile and cable routing from the XTR mountain design. Even in the SS design it has a slightly longer cage than most short cage road versions, allowing it to pair with the cassettes from 11-25 to 11-30. The engineers carried forward the direct mount option used in the mountain bike and R9100 designs. Clearly Shimano see's the movement towards thru-axle rear triangles in road bikes incorporating the direct mount option, which eliminates the B-link assembly and pivot, creating a stouter interface between frame and derailleur that results in even crisper shifting.

The rationale behind the Shadow style derailleur is simple and has clear benefit to all cyclists. The design sits much closer to the frame and under the cassette, protecting the cage from ground contact in case of accident or from bike to bike interaction when transporting multiple bikes. The pathway the derailleur action travels when shifted is also more linear, and smooth. Combined with refinements in the R8000 shifter mechanism, a shorter throw results in quicker, more precise shifts with less effort, even over the wider spread of the 11-34 cassette. Adding that greater range opens more cyclists up to various forms of road cycling, such as gravel, endurance, adventure, etc. One important difference between the mountain and road application of the Shadow design is the very welcome presence of a compact barrel adjuster for manual cable tension adjustments. The B-link standard hanger mount can be uncoupled from the direct mount pivot if your frame accepts the direct mount system.

Shimano's long experience with forging, machining and casting aluminum allows the engineers to make the body, links, and axles stiff, strong and light. Flouric coated link bushings keep the movement smooth and the linkage torsionally stiff and aligned. Unlike the R9100 model, the cage plates are made from machined aluminum, not CFRP, so you gain a few grams but gain max durability to go along with excellent cage stiffness. The cage design is torsionally and laterally stiff, resulting in reliable shifts and chain performance under load, no matter what ring and cog combination you find yourself in- all the way from 11-34 with the GS version. The upper and lower pulley wheels of the cage have specific profiles, and ride on Stainless Steel bolts that ensure longevity and resist corrosion.

The RD-R8000 Rear Derailleur is truly a game changer for many cyclists and conditions. The added range options are a serious benefit. With a 50-34 chainring set-up and an 11-34 cassette, you get a fully capable 1:1 ratio, better than many triple chainring set-ups of the past before cassettes hit 30T, without all the funky overlap and cross chaining "rules". That range is great but it is the engineering and mechanical advantages it engenders that truly make the shifting experience flawless, with noted Ultegra durability and efficiency- all part of Shimano's total integration ethos.