DIY Installation of GRX ST‑RX820 Di2 (future) Brake Sets for Gravel Bikes

The Shimano GRX ST‑RX820 Di2 (future) is a next-generation electronic shifter and brake lever unit built for gravel-specific performance. Its seamless integration with Shimano’s Di2 electronic shifting and hydraulic disc braking system ensures superior control and precision across mixed terrain. This guide offers a complete walkthrough for installing, adjusting, maintaining, and optimizing the GRX ST‑RX820 Di2 brake sets. Compatibility and comparison with other models are also discussed to help you get the most out of your gravel drivetrain.

Tools Required

  • 5 mm and 2.5 mm hex keys
  • Torque wrench (2–6 Nm range)
  • Shimano Di2 E-Tube project app (for setup/configuration)
  • Hydraulic mineral oil
  • Shimano funnel and bleed kit (for brakes)
  • Hose cutter and olive/insert press tool
  • Shimano SM-EW90 junction box (if applicable)
  • Clean rags and isopropyl alcohol
  • Internal routing tool (for Di2 wire management)

Unboxing and Preparation

Before starting the installation, inspect all contents of the GRX ST‑RX820 Di2 brake set. The set typically includes the left and right STI levers, pre-bled brake calipers, and pre-installed Di2 wires. Ensure your frame is Di2 compatible and has provisions for hydraulic hose routing. Confirm that your Di2 battery and derailleur systems are ready to integrate with the new levers.

Installing the Brake Levers

Start with mounting the levers on the handlebar. Slide each ST-RX820 Di2 lever onto the drop bar until it aligns with your preferred position. Use a 5 mm hex key to tighten the clamp bolt, setting torque to Shimano’s recommended 6 Nm.

Routing the Di2 wires is critical. Feed each wire internally through the handlebars to your junction box or central Di2 hub, such as the SM-EW90. Maintain slack to prevent tension when turning the bars. For clean wire management, use Shimano’s dedicated routing tools or internal sleeves.

Hydraulic Hose Connection

If hoses are not pre-installed or need trimming, use a dedicated hose cutter to ensure a square edge. Insert a new olive and barb fitting, then secure the hose into the lever port using Shimano’s hydraulic fitting bolt. Torque this to 5–6 Nm.

Route the hoses through the frame, avoiding sharp bends or kinks. At the caliper end, connect the hose using the included bolt and grommet system. Ensure a firm, leak-free seal before proceeding to bleeding.

Di2 Pairing and Configuration

Use the Shimano E-Tube Project app or desktop software to configure the Di2 system. Plug the levers into the Di2 junction box, then initiate system pairing. Set up multi-shift functionality, assign shift buttons, and update firmware as needed.

It’s crucial to check lever firmware compatibility with your derailleurs and junctions. The GRX ST‑RX820 Di2 (future) levers may offer new features that require updates across all components in the drivetrain.

Brake Bleeding and Pad Setup

With the levers and hoses installed, bleeding ensures consistent braking performance. Thread the bleed funnel into the lever reservoir and add Shimano mineral oil [paid link]. Open the bleed port at the caliper and squeeze the lever gently to push air bubbles out. Close the port once oil flows cleanly, then top off the reservoir.

Check that brake pads are aligned and secure within the caliper. Spin the wheel and squeeze the lever to bed the pads. Listen for any rotor rub and re-center the caliper using a 5 mm hex key if necessary.

Adjusting Reach and Free Stroke

The GRX ST‑RX820 Di2 allows fine-tuning of lever reach and free stroke. Use the small adjustment screws near the pivot to modify lever reach, enabling better control for riders with different hand sizes. Adjust free stroke to determine how soon the brakes engage after the lever is pulled.

These micro-adjustments greatly enhance comfort and performance over long gravel rides where modulation and grip fatigue matter.

Maintenance Best Practices

Keep the system clean by wiping the levers and calipers with isopropyl alcohol. Inspect Di2 wires for wear, especially near junctions and bar exits. Regularly check for hydraulic fluid leaks or decreased brake bite.

Shimano recommends bleeding the brakes every 6–12 months, depending on usage intensity. Keep firmware up to date to access the latest shifting features and ensure seamless component compatibility.

Troubleshooting Common Issues

Lever unresponsive during shifts:
Ensure full battery charge and verify wire integrity. Re-seat all connections.

Brake lever spongy or slow return:
Likely due to air in the hydraulic line. Re-bleed the system and check for leaks.

Inconsistent brake feel left vs. right:
Mismatched pad wear or caliper misalignment. Inspect pads and re-center calipers.

Shift lag or dropped commands:
May stem from outdated firmware or signal interference. Reboot the system and update software.

Customization and Performance Optimization

For advanced gravel tuning, riders can map shift functions differently between left and right levers. Customize button behavior using the E-Tube app, such as enabling full sequential shifting or modifying multi-shift sensitivity.

To reduce hand fatigue, combine the GRX ST‑RX820 Di2 levers with ergonomically flared gravel bars and gel-padded tape. Riders focused on racing can prioritize fast, crisp lever actuation and leverage the Di2’s low-latency performance for aggressive shifts.

Compatibility with Other Drivetrain Components

The GRX ST‑RX820 Di2 (future) is designed to work with Shimano’s 12-speed Di2 ecosystem. It integrates flawlessly with the RD-RX825 rear derailleur, FD-RX825 front derailleur, and BT-DN300 battery.

It uses SD300 series wires and is not backward compatible with SD50 (older generation) Di2 systems. Ensure you use only updated components from Shimano’s 12-speed Di2 line to prevent functionality loss or firmware conflicts.

Comparison with Similar Models

Compared to the previous GRX ST-RX815, the ST-RX820 Di2 features faster actuation and enhanced lever ergonomics. The button surface is improved for better control in off-road conditions, and the firmware introduces smarter shift logic.

Against the Ultegra ST-R8170, the GRX model offers more aggressive lever texture and better modulation tuned for gravel riding. While Ultegra is optimized for road dynamics, the GRX ST‑RX820 Di2 is tailored for mixed-terrain control and endurance.

Conclusion

The Shimano GRX ST‑RX820 Di2 (future) brake lever system represents a high-performance upgrade for gravel cyclists who demand electronic precision and hydraulic stopping power. When properly installed and maintained, it offers unbeatable responsiveness, configurability, and reliability on dirt, gravel, and road alike. With attention to detail in routing, setup, and configuration, you can unlock the full potential of your Di2 gravel setup.