Shimano dura ace di2 r9150 rear derailleurthe dura ace r9150 rear derailleur takes shadow technology from shimanos mtb range and introduces it to the road the shadow design places the rear derailleur under the chainstay and cassette to give a slimmer profile which not only improves aerodynamics but helps prevent damage in a crash the shadow design offers faster wheel changes thanks to the fact that it moves the derailleur out of the way of the dropouts it also offers faster and more precise