The Shimano GRX ST‑RX820 Di2 (future) represents a modern evolution in gravel-specific braking and shifting components. Designed to meet the demands of mixed-terrain riding, it combines electronic precision with Shimano’s legacy of mechanical reliability. This guide offers an in-depth look at how to install, adjust, and optimize this advanced brake set, alongside a technical breakdown of its key features, compatibility, and comparative value.
Tools Required
- 4mm and 5mm Allen keys
- Di2 EW-SD300 wires
- Shimano Hydraulic Disc Brake Bleed Kit
- Shimano Mineral Oil [paid link]
- Torque wrench
- Di2 Junction Box (EW-RS910 or similar)
- Isopropyl alcohol and clean cloths
Installation of the GRX ST‑RX820 Di2 Brake Levers and Calipers
Installation begins with proper frame preparation and attention to cable routing. Since this is a semi-wireless Di2 system, only the front derailleur, rear derailleur, and internal battery require wired connections.
Start by mounting the brake calipers on flat-mount bosses. Align each caliper to the rotor and torque to specification. Attach the brake hoses to each lever, route internally if the frame permits, and cut to length. After inserting olives and barbs, secure the hoses into the levers using a 5mm Allen key.
Install the ST‑RX820 Di2 levers onto the handlebar, ensuring the lever reach is symmetrical. Connect the Di2 wires from the levers to the junction box using EW-SD300 connections. Use a firmware update via E-Tube Project to ensure compatibility and optimal performance.
Follow with a complete hydraulic brake bleed to remove air and optimize braking response. Secure all Di2 wires with adhesive cable guides or internally where frame provisions exist.
Adjusting the GRX ST‑RX820 Di2 Brake Set
Proper adjustment ensures both braking consistency and comfort on rugged gravel trails.
Start by centering the brake calipers. Loosen the caliper mounting bolts, squeeze the brake lever, and retighten while holding pressure. Inspect rotor alignment by spinning the wheel—rotors should spin without contact.
For lever reach adjustment, use the screw on the inside of the brake lever body. This allows riders to customize ergonomics, especially useful for smaller hands or varied grip styles.
Free stroke adjustment is also possible via a dedicated screw on the reservoir cap. It determines the lever travel before pad engagement. Make small changes incrementally and test on steep gradients to assess the modulation.
Electronic shifting calibration is done through Shimano’s E-Tube Project app. Customize shift speeds, multi-shift functions, and assign shift buttons to preferred derailleur actions.
Routine Maintenance for Long-Term Reliability
Regular servicing of the ST‑RX820 Di2 brake set prevents performance degradation. Focus on brake fluid replacement every 12–18 months, particularly in dusty or wet climates.
Clean brake rotors and pads periodically using isopropyl alcohol. Inspect pads for uneven wear and replace if the material is less than 0.5mm thick. Lubricate lever pivot points annually to maintain smooth actuation.
For the Di2 system, periodically check wire connections and battery levels. Shimano’s firmware should be updated as new versions become available to maintain compatibility with other drivetrain elements.
Troubleshooting Common Setup Issues
1. Brake rub after installation: This typically indicates improper caliper alignment. Re-center the calipers and verify rotor trueness.
2. Spongy brake feel: Air in the hydraulic line or low brake fluid is often the cause. A complete bleed will resolve this.
3. Lever not returning properly: Inspect for contaminated fluid or friction in pivot points. Clean and lubricate as needed.
4. Shift lag in Di2 system: Ensure full battery charge and check wire connections. Firmware updates may also fix latency issues.
5. Noise during braking: Could result from glazed pads or rotor contamination. Lightly sand pads or replace them, and clean rotors.
Customization and Optimization Tips
The ST‑RX820 Di2 system allows advanced customization through Shimano’s E-Tube app. Riders can remap shift functions, adjust multi-shift behavior, and select between synchronized or semi-synchronized shifting modes.
Mechanical ergonomics can be optimized by adjusting the hood position on the bar. Riders with aggressive bike fits can rotate the levers inward for improved wrist alignment on descents.
For braking power modulation, combining Ice-Tech rotors with resin pads reduces heat build-up while offering a quieter ride. Upgrading to a 180mm rotor up front is also recommended for riders tackling steep and prolonged descents with loaded bikes.
Compatibility with Other Drivetrain Components
The GRX ST‑RX820 Di2 is part of Shimano’s 12-speed gravel-specific groupset, making it fully compatible with:
- GRX RD‑RX820 rear derailleur
- GRX FD‑RX820 front derailleur
- Shimano 12-speed chain and cassette (road configuration)
- BT-DN300 internal battery
- EW-SD300 series wires
- Compatible Di2 shifters and satellite buttons
This brake set is not compatible with 11-speed Di2 components or older EW-SD50 wire systems. Mixing with non-GRX calipers or levers will compromise braking and shift performance.
Comparing the GRX ST‑RX820 Di2 with Similar Models
When compared with the GRX ST-RX810 (11-speed mechanical), the ST‑RX820 Di2 offers major advancements in ergonomics, shifting precision, and wireless integration. Brake feel is more progressive, and the lever design is refined for longer rides.
Versus the Shimano Dura-Ace R9270, the GRX variant provides better modulation and comfort for off-road use, although the Dura-Ace set offers lighter weight and marginally faster shifting.
Compared to SRAM Force eTap AXS, Shimano’s GRX Di2 holds an edge in shift customization and brake modulation, though SRAM’s wireless integration is simpler to install.
FAQs
1. Is the GRX ST‑RX820 Di2 compatible with mechanical derailleurs?
No, it is an electronic-only shifter and must be paired with GRX Di2 derailleurs.
2. Can I use GRX ST‑RX820 Di2 on a road bike frame?
Yes, if the frame has flat-mount caliper mounts and is Di2-compatible.
3. Does it support Synchro Shift?
Yes, both Synchro and Semi-Synchro shifting are supported via the E-Tube Project app.
4. What battery does it require?
It requires the Shimano BT-DN300 internal battery.
5. Are shift buttons customizable?
Yes, each button’s function can be reassigned in the E-Tube Project app.
6. How do I update the firmware?
Use the E-Tube Project app on a PC or mobile device with a USB or Bluetooth connection to the junction box.
Conclusion
The Shimano GRX ST‑RX820 Di2 brake set stands as a top-tier choice for gravel riders seeking seamless integration, superior ergonomics, and highly customizable performance. With precise braking, advanced electronic control, and a design tailored for off-road endurance, it offers clear advantages over both mechanical and competitor systems. For riders committed to serious gravel adventures, this model delivers confidence, control, and cutting-edge innovation.