The new wireless Di2 platform ensures fast and smooth shifting at the derailleur. It also offers a choice between manual shifting and synchronized shifting assist modes – SEMI-SYNCHRO or FULL-SYNCHRO – that feel like your own personal assistant! In SEMI-SYNCHRO mode, the derailleur automatically adjusts to avoid large jumps in gear ratios, allowing you to maintain your cadence and rhythm. In FULL-SYNCHRO mode, the derailleur and front derailleur work harmoniously together, so you always have the correct gear engaged and no longer need to worry. Seamless communication with the derailleur, combined with programmed control of the chain guide, minimizes the risk of the chain dropping. The maximum tooth count is 50-52T. It’s entirely up to you how often you want to think about the gear ratio!