Shimano’s GRX ST‑RX820 Di2 (future) brake sets represent a significant advancement in road and gravel braking performance. Developed for mixed-terrain and adventure riders, this component integrates Di2 electronic shifting with refined hydraulic braking into a cohesive unit. Whether you’re descending a gravel pass or navigating traffic in wet weather, the GRX ST‑RX820 Di2 offers precise, controlled, and consistent stopping power that sets a new benchmark in braking systems.
Tools Required:
- 5mm Allen wrench
- Torque wrench (preset to Shimano specs)
- Shimano mineral oil [paid link]
- Bleed kit for Shimano road disc brakes
- Bar tape and scissors
- Di2 wire tool
- Hydraulic hose cutter and press
- Isopropyl alcohol and clean rags
Installation Procedure
Installing the GRX ST‑RX820 Di2 brake levers requires attention to both electronic and hydraulic components. Begin by routing the Di2 wires through the handlebars, ensuring a clean path to the junction box and battery. Shimano’s E-Tube app allows setup and customization once the system is powered.
Mount the shifters on the handlebar using a 5mm Allen wrench. It’s crucial to maintain ergonomic positioning—angled slightly inward—for optimized comfort during long rides. Hydraulic hoses should be measured, cut precisely, and pressed into the levers using the proper Shimano connector tools.
Next, connect the calipers using Shimano’s flat-mount hardware. Torque all bolts to the manufacturer’s specifications. Finally, bleed the hydraulic system using Shimano mineral oil to remove air pockets and ensure crisp, responsive braking from the outset.
Adjustment for Maximum Braking Performance
Fine-tuning is essential to unleash the full braking potential of the GRX ST‑RX820 Di2. Begin with lever reach adjustment using the screw located near the pivot point. Riders with smaller hands will benefit from bringing the levers closer to the bar.
Caliper alignment is another critical step. Loosen the mounting bolts, squeeze the brake lever, and retighten to self-center the caliper over the rotor. For any residual rubbing, use micro-adjustments to reposition the caliper.
Brake pad spacing can be monitored using the pistons. Over time, they may require resetting with a plastic piston press tool. Keep the rotors clean by wiping them regularly with isopropyl alcohol to maintain friction integrity and prevent glazing.
Maintenance Requirements
The GRX ST‑RX820 Di2 system is designed for durability, but proactive maintenance ensures long-term reliability. Inspect brake pads every 500–1000 kilometers, depending on terrain and conditions. Replace pads when the remaining thickness drops below 0.5mm.
Brake fluid should be flushed annually or after wet, muddy rides. Air contamination leads to spongy lever feel, which compromises braking efficiency. Use Shimano’s bleeding kit and follow the step-by-step bleed procedure for consistent hydraulic performance.
Keep the Di2 software updated via the E-Tube app. Regular firmware checks ensure the latest performance enhancements and compatibility patches are installed.
Troubleshooting Common Setup Issues
Some users may experience inconsistent lever feel or pad rubbing after installation. This often traces back to improper bleeding or caliper misalignment. Repeating the bleed process and re-centering the calipers usually resolves the issue.
If electronic shifting doesn’t engage, check Di2 wire connections and battery charge levels. The integrated junction system can be difficult to troubleshoot without Shimano’s diagnostic tool, so ensure every connection is firm and directionally correct.
Noise during braking typically results from contaminated rotors or pads. Clean thoroughly and consider sanding the pad surface lightly to restore optimal contact.
Customization and Performance Optimization
Shimano’s E-Tube Project app allows riders to tailor the GRX ST‑RX820 Di2’s braking and shifting functions. Shifting buttons on the brake levers can be reprogrammed for alternative functions such as dropper post activation or rear derailleur multi-shift.
Brake modulation—the balance between light braking and full-stop—is highly refined in this model. Riders can experiment with different pad compounds (resin vs. metallic) to match terrain preferences. Resin offers quieter braking; metallic provides better heat resistance during long descents.
Pairing the system with 160mm rotors front and rear maximizes stopping power for loaded bikepacking setups, while 140mm options cater to lighter riders or smoother terrain.
Comparison with Similar Brake Levers
Compared to previous generations like the GRX ST-RX815, the ST‑RX820 Di2 offers a notably improved lever feel and shorter stroke for quicker response. Shimano refined the servo-wave mechanism to deliver more power at the start of the lever pull—ideal for technical descents and emergency stops.
In contrast to Shimano’s Ultegra and Dura-Ace Di2 levers, the GRX variant features a more textured lever blade and ergonomic profile designed specifically for off-road riding. The larger hoods increase comfort during long rides on mixed terrain.
Versus SRAM’s Rival eTap AXS levers, the GRX ST‑RX820 Di2 provides a more analog braking feel with better mechanical feedback, despite being an electronically integrated system.
Compatibility with Other Drivetrain Components
The GRX ST‑RX820 Di2 integrates seamlessly with Shimano’s 12-speed GRX drivetrain components. It pairs with both the RD-RX820 rear derailleur and FD-RX820 front derailleur. Mixing with Ultegra 12-speed Di2 derailleurs is not officially supported due to firmware and shifting protocol differences.
Hydraulic calipers must be Shimano flat-mount road or gravel-specific units, such as BR-RX820. Mixing calipers from other groupsets may alter pad contact timing and lever feel.
For handlebars, Shimano recommends a 31.8mm clamp diameter and internal cable routing capacity. Ensure your frame supports internally routed hydraulic and Di2 wiring for optimal integration.
Conclusion
The GRX ST‑RX820 Di2 brake sets exemplify Shimano’s commitment to precise engineering tailored to real-world riding conditions. Their combination of electronic shifting integration and hydraulic braking performance marks a significant step forward in bike component technology. With proper installation, regular maintenance, and thoughtful customization, this braking system will deliver unmatched control and stopping power for gravel and adventure riders alike.