Building a 105 Di2 bike from parts means chasing down individual SKUs across levers, derailleurs, chain, cassette, battery, and wiring — and one wrong part number can hold up a build for a week. This kit bundles the Di2-specific pieces of the R7170 group into a single order: ST-R7170 shift/brake levers with matched BR-R7170 hydraulic calipers, both derailleurs, the CS-R7100 11-34 cassette, a CN-M7100 chain, the BT-DN300 seatpost battery, and the EW-EC300 charger. What it doesn't include are the parts where frame fit or rider preference drives the spec: crankset, bottom bracket, disc rotors, and the EW-SD300 wires that connect the derailleurs to the battery.

R7100-series 105 exists only as Di2 — Shimano moved the entire 105 group to electronic shifting for this generation, so there's no mechanical R7100 variant. The system runs semi-wireless: the shift levers communicate with the derailleurs over a wireless signal, while the derailleurs themselves stay wired to the seatpost battery via EW-SD300 e-tube wires. That keeps the cockpit clean with no cables running through the bar or stem, and it means routing a new build is dramatically simpler than the previous 11-speed Di2 platform.

The ST-R7170 levers use CR1632 coin cells that Shimano rates at roughly four years of service in the 105 version — longer than the Ultegra and Dura-Ace lever runtime because the 105 shifters do not support wired operation. The one gotcha worth flagging up front: the 105 shift levers cannot be wired to the rest of the system. They only have a single SD300 port for firmware updates and diagnostics, so the shifter-to-battery link is wireless-only. If your frame or fit needs a wired shifter setup, step up to Ultegra R8170 or Dura-Ace R9270.... Read More