Shimano's Di2 electronic shifting system is ruthlessly efficient, utterly reliable, and a pure joy to use. The development of Dura-Ace R9100, with it's R9150 Di2 components, brought about some exciting changes, such as the SynchroShift options, as well as Instant Release at the shift levers, which eliminated the intentional hesitation at the shift release before the shift took place. Now that is gone and the results are both obvious and welcome when dropping a gear. In reality this is really the only easily identifiable change noticed while riding with the Dura-Ace RD-R9150 Di2 Rear Derailleur. This is due to the fact that the shifting of it's predecessors has been fantastic, with impressive accuracy and operation at all times. Both SynchroShift and Instant Release come from XTR M9050 system, as does the new configuration of the body to the low-profile Shadow RD design. The final major change is that the short cage SS rear derailleur is now capable of handling an 11-30T max cassette, up from the 28T of the 9050 version. Shimano didn't stop the evolution there, with consideration to a few frame manufacturers (and thinking forward to more) that offer a direct mount system for the rear derailleur. The RD-R9150 offers that flexibility in a first for road bike use. At 204 grams, with sealed electronics and servo motor, you get premium shifting performance, high-end materials, supremely integrated engineering, and impeccable shifting from Dura-Ace Di2.

Shimano's E-Tube connection system is the neural network of Di2, with ease of use and flexibility of set-up paramount. The RD-R9150 features a single E-Tube port, which when fully connected to the E-Tube system and internet access via USB, App or program, allows you to program the system to your preferences and upgrade the firmware for the rear derailleur. The waterproof housing that protects the electronics is made from both aluminum and Carbon Fiber Reinforced Plastic (CFRP), which makes the housing strong and resistant to impact. Mechanically, the parallelogram movement of the derailleur glides on four Flouric-coated bushings, which run smoothly for tens of thousands miles of use and never need servicing. Shimano constructs the body from aluminum, in a way that no bicycle but Shimano can. The stiffness and precision reflect very high level engineering and construction. The derailleur cage is made from two plates of CFRP, shaped for maximum torsional stiffness, carrying the 11T sealed bearing guide and tension pulley wheels. These composite pulleys are specific in purpose, but equally durable, ready for years of smooth shifting mileage ahead.

If you do have a direct mount frame design, the knuckle for the derailleur hanger mount is removable. You simply fasten through the exposed hole. The Shadow RD cage design takes the mountain system to the road, bringing the rear derailleur much closer to the frame, seriously reducing not only the risk of damage when transporting or in a crash, but also cleans up some airflow around the rear dropout. Every little bit helps! If you have an existing Dura-Ace 9050/70 or Ultegra 6870 Di2 system, you can upgrade your STI levers and rear derailleur to gain the additional gearing range and Instant Release with no other change necessary. To get the full range of features you would need to commit to new E-Tube and/or battery options (depending on your current set-up), as well as the FD-R9150 Front Derailleur. No matter your choice, the benefits in performance, Shadow RD, and range will be well worth your investment. Stay ahead of the field with the Dura-Ace RD-R9150 Di2 Rear Derailleur.