Shimano's derailleurs have always been superlative, and the new Dura Ace RD 9000 is no exception. It makes intelligent use of carbon fiber, but still relies primarily on its alloy construction to get the job done smoothly, quietly, and efficiently. Oh, and it'll pretty much last forever, too. One of the most significant revisions in the 9000 series was a reduction in the force required to initiate a shift at the lever. Shimano had to move cable attachment points around a bit to achieve this, but it's immediately noticeable when you shift. Shimano's returned to a carbon fiber cage, which helps reduce vibration in the derailleur, and ensures a perfectly smooth shift both up and down the cassette. The RD9000 is capable of handling a 28 tooth cassette, and it'll feel the same as shifting on a corncob 11 23.