The Shimano GRX Di2 RD-RX825 brings flagship electronic precision to the gravel world, pairing instant wireless shifting with SHADOW RD+ chain stabilisation so you can charge rough terrain with complete confidence in your drivetrain. Designed specifically for 2x12-speed gravel riding, it serves as the communication hub of the entire GRX Di2 system.

Highlights

• 12-speed Di2 electronic shifting: instantaneous, repeatable actuation on every gear change, regardless of conditions.
• SHADOW RD+ clutch: adjustable chain stabiliser suppresses chain slap on gravel, cobbles, and rough descents for quieter, more controlled riding.
• Integrated wireless connectivity: built-in Bluetooth LE and ANT+ unit communicates with shift levers, compatible cycle computers, and the E-TUBE PROJECT Cyclist app.
• Integrated charge port and LED indicator: the EW-EC300 charge port and status LED are built directly into the derailleur body, eliminating the need for a separate junction box.
• ON/OFF clutch switch: disengage the SHADOW RD+ tension in seconds for easy rear wheel removal — no tools required.
• Synchronised Shift modes: supports Full and Semi-Synchronised shifting for automatic front/rear coordination, reducing rider input on mixed-terrain routes.
• 36T maximum low sprocket: accepts cassettes up to 11-36T to suit varied gravel terrain and climbing demands.

Electronic Architecture

The RD-RX825 acts as the wireless hub of the GRX Di2 drivetrain, connecting to ST-RX825 shift levers and pairing with compatible Garmin, Wahoo, and other ANT+/Bluetooth cycle computers via E-TUBE PORT. A single EW-SD300 port connects to the BT-DN300 internal battery, while the multi-function button enables on-the-fly adjustment of Synchronised Shift modes without stopping. The integrated LED provides clear battery status at a glance.

SHADOW RD+ Technology

Shimano's SHADOW RD+ clutch applies additional friction to the derailleur pivot, dramatically reducing chain bounce on unpredictable gravel surfaces. The external ON/OFF switch makes disengaging the clutch for wheel changes a one-second operation. When engaged, the mechanism preserves smooth drivetrain feel while keeping the chain locked down over the roughest terrain.

Compatibility & Fit

The RD-RX825 is designed for 2x12-speed GRX Di2 drivetrains. It accepts cassettes with an 11T minimum sprocket and up to a 36T maximum low sprocket, with a 40T total capacity. Compatible cassettes include CS-R8101-12 (11-34T) and CS-HG710-12 (11-36T). Compatible shifters include ST-RX825, ST-R9250, and ST-R9270. Compatible with 12-speed Shimano chains. Mount type: standard 10x1 / Shimano Rear Direct Mount compatible. Also fully compatible with existing 12-speed road Di2 components.