Understanding Di2 derailleur specifications
Shimano front derailleur and rear derailleur specifications... what do they mean, really? This page explains all of them, and why they matter.
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.
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:
Specifications
- 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 all componentsRelated pages
12-speed Di2 New User Guide
Just bought a new 12-speed Di2 bike? This page explains what the buttons do, how to charge, and what synchronized shfit does.
Installing a new chain - length and direction
Sizing and installing a new chain for your Di2 bike isn't hard, you just need to follow the right steps. Read this page to learn more.
12-speed Rear Derailleur installation and adjustment guide
This page shows you how to install your 12-speed Di2 rear derailleur, set the B-screw, limits, and fine-tune the shifting using micro-adjust
Synchronized Shifting - the complete guide
Synchronized Shifting - what is it exactly? What does it do and how can you set it up? This page will guide you through the process of setting up synchro shift.
Manuals & other documents
Firmware updates
Below is an overview of all known firmware updates for this component. The changelog texts are Shimano's, and quite often they're a bit cryptic - sorry!
4.2.3
■ ChangesSecurity performance for wireless communications between the shifter and rear derailleur has been improved.Click here to view FAQs for more information. https://bike.shimano.com/faq/DI20A#D-7030*The firmware for both the shifter and rear derailleur must be updated for proper operation of the Di2 system.■ OthersGeneral bug fixes.
4.2.0
- The FRONT SHIFT NEXT function is now supported.- General bug fixes.
4.1.1
The issue where the rear derailleur cannot be adjusted on E-bikes with a third-party drive unit has been fixed. - The issue where the rear derailleur cannot be adjusted using E-TUBE PROJECT Cyclist has been fixed. *If you are experiencing this issue, SM-PCE02 and E-TUBE PROJECT Professional are required to perform an update. Please contact your place of purchase.
4.1.0
- EW-EX310 is now supported. - Fixed identified issues.
4.0.7
Stabilized the wireless shifting operation and optimized the LED display.
4.0.4
Firmware released.
More images