At a time when electronic drivetrains are gaining unstoppable traction, we appreciate that Shimano chose not to neglect its storied pro-level mechanical drivetrain for Di2, making careful, meticulous updates that have resulted in subtle, but significant, improvements to functionality. For those of us who still unabashedly believe in the soul of mechanical shifting, the Dura-Ace RD-R9100 11-Speed Rear Derailleur feeds our love for self-actuated shifting with a more protected position and cleaner mounting interface. When redesigning Dura-Ace, Shimano carried over the modifications to the rear derailleur shaping from Di2 to 9100. That involved altering the low-profile Shadow design slightly to better protect it in the event of a crash. This slimmer, more streamlined shape integrates expertly with the sleek aesthetics of the Dura-Ace 9100 drivetrain as a whole, delivering smoother lines and a less utilitarian appearance. Shimano also worked to improve shifting efficiency on the rear derailleur, constructing the pulley to remain a consistent distance away from the cassette for more dependable shifts. The shorter, effortless shift throws on the levers result in crisp chain jumps up and down the cassette all day long with no sign of getting bogged down. Shimano also looked to its mountain drivetrains when reworking the rear derailleur's mount, adopting its Direct Mount interface to add stability and offer more efficient cage alignment.