Equipment > Components > Derailleurs > Road - Rear
Description
Junction box functionality now lives in the rear derailleur with Shimano's 12-speed Di2 architecture, and the RD-R8150 handles those responsibilities alongside its primary job of moving the chain across the cassette. The derailleur body integrates the charging port, LED status indicator, function button, and D-Fly wireless communication system that previously required a separate junction component. If you've dealt with Junction A placement challenges on previous Di2 builds, the consolidated design simplifies routing and reduces potential failure points.
Shimano rates the R8150 as 58% faster than the previous-generation Dura-Ace RD-R9150, which was already fast. The motor and gear mechanism deliver shifts that complete before you've finished the thought of wanting a different gear. Under load, cross-chained, mid-climb, the derailleur executes shifts with the same precision regardless of conditions. That speed comes from updated motor technology and the Hyperglide+ cassette tooth profiling that guides the chain onto each cog with reduced resistance.
The shift levers communicate wirelessly with the rear derailleur, sending commands via a secure wireless protocol. The derailleur itself connects to the BT-DN300 internal battery via an EW-SD300 wire, as does the front derailleur. This hybrid architecture keeps the high-current motor connections wired for reliability while eliminating the cable routing complexity at the cockpit. You can wire the shifters too if you prefer, but most builds benefit from the wireless option, especially with modern integrated cockpit designs where internal routing to the bars becomes challenging.... Read More
Features
- 12-speed Di2 electronic rear derailleur for Ultegra R8100 systems
- 58% faster shifting than previous-generation Dura-Ace RD-R9150
- Integrated wireless unit, charging port, LED indicator, and function button
- Single cage length compatible with 11-28T, 11-30T, and 11-34T cassettes
- 39T total capacity, 16T maximum front chainring difference
- Shadow RD low-profile geometry
- Wireless communication with shift levers, wired connection to BT-DN300 battery
- Direct attachment and direct mount compatible
- Aluminum cage plates, GFRP body, composite pulleys
- 11T guide and tension pulleys with sealed bearings
- Four fluorine-coated link bushings
- Charging cable (EW-EC300) and battery (BT-DN300) sold separately
- 262 grams