Shimano ST-9070 Dura Ace Di2 Rear Derailleur
It's hard to believe that electronic shifting has been in our vocabulary, let alone on our bikes, for less than half a decade. And while electronic perfection has now become the en-vogue aspiration point for engineers, it's easy to forget that Shimano got the bandwagon kick-started. We still remember the dropped jaws and even the skeptical and naysayers at the advent of 7970. We understood: it was relatively unproven technology. But now, we've already witnessed the unbranded prototype power of the Dura-Ace RD-9070 Rear Derailleur under the legs of pro teams throughout the 2012 season. Accordingly, we hold no reservation in saying that 9070 is perfection perfected. You can even program the number of gears that you're running, a vital application given that 9070 operates with both 10- and 11-speed cassettes.