Improvements Shimano has made to the latest Ultegra Di2 group are truly remarkable, and while we always wish we had a full Dura-Ace build it will be difficult for us to recognize the difference in performance. It makes sense as Ultegra uses Dura Ace percolation technology and for the rear derailleurs, the RD-R8050 borrows heavily from the top-of-the-line Dura-Ace RD-R9150 including the low profile Shadow design. This profile places it closer to the frame and tucks the derailleur under the cassette. This protects the switch in the event of an accident and generally from impacts so it stays better aligned, making shifts smoother fast and accurate. New RD-8050 geometry allows for shorter throws resulting in faster and more precise shifting even across a wider range of 11-34 cassettes.

We are amazed by the performance of Shimano Di2. Switches using a spring and cable tension to move the chain from gear to gear seem almost archaic compared to electronic rear derailleurs which use innovative digital technology to send electronic signals to the motor to precisely position the circuit exactly there where it is needed on the cassette. Shifts happen much faster and with less effort. Shimano even uses a safety mechanism which disables the rear derailleur so it can withstand side impacts without damaging the component. Shimano's superior E-Tube software allows for full customization , including shift speed, number of gears switchable by pressing and holding the button, and even then which button does what.

Note on cage length: Shimano offers the 8050 derailleur in two cage versions: SS version , which works with gears up to 30 teeth. , and the GS version with a medium cage which works with gears up to 34 teeth. GS version can be used with Dura Ace Di2 if you want to use a 32T or 34T cassette with a Dura Ace group as this group only offers one short cage rear derailleur option.