E-TUBE#

E-TUBE is Shimano’s proprietary wired communication bus connecting all Di2 electronic shifting components. It is the internal nervous system of the Shimano GRX Di2 groupset on the Canyon Grizl CF 8 Di2.

In the Network#

E-TUBE is entirely internal to the Di2 system. All external wireless communication (to the Garmin Edge MTB) is handled by the D-Fly wireless module, which bridges E-TUBE to ANT+ and Bluetooth LE.

Shift levers ──E-TUBE──► Junction Box A2 ──E-TUBE──► Rear Derailleur (motor)
                                │                   ──E-TUBE──► Battery (BT-DN320)
                                │
                         D-Fly Module (EW-WU111)
                                │
                         ANT+ broadcast ──────────► Garmin Edge MTB
                         Bluetooth LE ─────────────► E-TUBE Project App

Components Connected#

Component	Model	E-TUBE Role
Shift/brake levers	ST-RX825	Sends shift commands
Rear derailleur	RD-M8250	Receives commands, executes shift
Internal battery	BT-DN320	Power supply, charge state reporting
Junction box A2	EW-RS910	Signal hub, USB-C charging port
D-Fly wireless module	EW-WU111	Bridge to ANT+ and BLE

Key Characteristics#

Attribute	Spec
Bus type	Proprietary serial
Connector	EW-SD300 / EW-SD50 (multi-pin)
Topology	Daisy-chain or star via junction box
Power	Carried on the same cable as data

E-TUBE cables carry both power and data on the same wire. The battery powers all components through the junction box; the junction box routes signals between levers, derailleurs, and the wireless module.

D-Fly: The Wireless Bridge#

The D-Fly module (EW-WU111) connects to the E-TUBE network and broadcasts Di2 status wirelessly:

Protocol	Data
ANT+ (Shifting profile)	Current gear position (front/rear), battery level, shift count
Bluetooth LE	E-TUBE Project app connectivity for configuration and firmware updates

This is what makes Di2 data visible on the Garmin Edge MTB — the Edge receives the ANT+ Shifting broadcast and displays current gear and battery on-screen, logging both to the .fit file.

E-TUBE Project App#

Shimano’s companion app (iOS / Android / Windows) connects via Bluetooth LE to the D-Fly module. Functions:

Feature	Detail
Button remapping	Assign any function to any lever or satellite button
Adjust shift timing	Fine-tune derailleur response speed
Firmware updates	Over-the-air via BLE or wired via junction box USB-C
System diagnostics	Per-component battery level, connection status
Synchro Shift	Automatic front/rear coordination (2× systems only)