Wide 36T-compatible 12-speed Di2 rear derailleur. Receiving the wireless shifting signal from the shift lever, the SHIMANO 105 rear derailleur completes a shift in the blink of an eye with its high-performance motor and optimized link structure. This is the hub of the Di2 system, with the charging port, indicator LEDs, adjustment switches and more integrated into a compact package. A low-profile design reduces damage from contact and falls.