XT 11-speed Di2If you are used to riding with external gears or just want the most efficient powertrain when riding, this is the one you want. External gear systems offer the best power transfer. There is less energy getting lost in space, so every bit of raw power you put into your pedals will be transferred almost directly into your forward momentum and getting you where you need to be. The external derailleur and cassette variant. Expanding on the eBullitt