Shadow Rear Derailleur (12 speed)

Shadow Rear Derailleur (12 speed)

Ultegra RD-R8150

The RD-R8150 rear derailleur is part of Shimano's new 12 speed system, allowing for both wired and wireless communication between the derailleur and shift levers.

It is used with the newer battery, the BT-DN300.

This derailleur features a charge port, LED, button and an EW-SD300 type port used to connect the derailleur to the battery. Both the rear derailleur and the front derailleur connect to the battery using a wire. The shift levers send their shift commands to the rear derailleur wirelessly.

Affiliate Links

Using the affiliate links to purchase anything earns the site a small commission, at no additional cost to you.


These 12-speed derailleurs use the same charger as the new Di2 power meters, and perhaps even better: the port cover can be replaced when broken.

Cross-chaining is not blocked

11-speed Di2 had a feature called Gear Position Control that effectively locked out the smallest two cassette cogs when in the small ring at the front. This feature is not enabled for 12-speed Ultegra and 105 derailleurs.

If you're on 12-speed Ultegra or 105, you can shift into the smallest cassette cogs when you're in the small ring. There is no way to change this setting.

LEDs and button cheat sheet

Keep having to go back to the manual to read what the LEDs mean or what the button does? Download my Cheat Sheets, print them, and keep them close to your bike. That way you'll never have to look for the manual again.

Di2 Cheat Sheets.

Crash Mode Reset

Since the main junction functionality has moved to the rear derailleur, Shimano also changed the method of getting out of crash mode. Pressing the button on the rear derailleur would be hard during a race, so you can now shift out of crash mode.

To get out of crash mode on 12-speed road bikes, shift up and down the entire cassette. This video by Rides of Japan explains it well:


  • Model code: RD-R8150
  • Series: Ultegra (R8100)
  • Weight: 262g
  • Speeds: 12
  • Number of switches: 1 (function button)
  • SD300 ports: 1
  • Max front difference: 16T
  • Total capacity: 39T
  • Low sprocket max: 34T
  • Low sprocket min: 30T
  • Top sprocket min: 11T
  • Top sprocket max: 14T
  • Pulley teeth: 11
  • Wireless connectivity: Bluetooth / ANT
  • Mount: Direct mount / conventional
  • Charging port: Yes
  • Charger: EW-EC300
  • RD type: Shadow RD
  • Clutch: No

Related components

View the Electric Wire / E-Tube cable (EW-SD300)


Electric Wire / E-Tube cable

View the Internal Battery (BT-DN300)


Internal Battery

View the Front Derailleur (FD-R8150-F)


Front Derailleur

View the Disc Brake Dual Control Lever (Wireless) (ST-R8170)


Disc Brake Dual Control Lever (Wireless)

View the Rim Brake Dual Control Lever (Wired) (ST-R8150)


Rim Brake Dual Control Lever (Wired)

View the Internal Battery Charging Cable (EW-EC300)


Internal Battery Charging Cable

View the Satellite Drops Sprint Shifter (12 speed) (SW-RS801-S)


Satellite Drops Sprint Shifter (12 speed)

View the 2x12 Crankset (FC-R8100)


2x12 Crankset

Related pages

More images