Shimano’s GRX ST‑RX820 Di2 (future) brake set exemplifies a new frontier in gravel-oriented electronic shifting and braking systems. Tailored specifically for off-road endurance and mixed-terrain riding, the RX820 Di2 integrates advanced ergonomics with wireless electronic control and superior braking performance. This guide delivers a detailed breakdown of its installation, tuning, maintenance, and optimization to help riders and mechanics alike fully understand the capabilities and technical nuances of this high-performance component.
Tools Required
- 5 mm and 4 mm hex wrenches
- Shimano TL-BH62 hose cutting and insertion tool
- Bleed kit compatible with Shimano hydraulic systems
- Shimano mineral oil [paid link]
- Torque wrench (2–10 Nm range)
- Di2 wire tool (TL-EW300)
- Compatible bleed block
- Isopropyl alcohol and clean rags
Component Overview and Specifications
The GRX ST‑RX820 Di2 combines wireless shifting with a wired power connection for reliability and reduced cockpit clutter. Paired with Shimano’s 12-speed Di2 groupset, it delivers low-latency shifting and powerful hydraulic braking.
The levers feature:
- Optimized gravel-specific ergonomics
- Raised grip texture for glove use
- Separate control for each brake and shifter
- Hidden Di2 ports for a clean bar layout
- Shimano E-Tube Project compatibility for firmware updates and customization
Installation of the GRX ST‑RX820 Di2 Brake Levers
Installing the GRX ST‑RX820 Di2 brake levers requires precision to ensure both electronic shifting and hydraulic braking systems function optimally. Start by routing hydraulic hoses and Di2 wires, taking advantage of the system’s semi-wireless configuration for a cleaner cockpit.
Begin by installing the Di2 levers onto the handlebars using a 5 mm hex wrench. Torque should not exceed 8 Nm. Once secured, route the hydraulic hose through the frame and connect it to the caliper. Ensure the Di2 wire connects correctly to the in-frame junction box if a satellite button or remote display is used. Before finalizing, test for lever clearance and proper ergonomic angle suitable for the rider’s hand size and riding posture.
Brake Hose Setup and Hydraulic Line Bleeding
A clean and secure hydraulic hose setup is vital for brake performance. Use the TL-BH62 tool to cut the hose and insert the barb and olive cleanly before tightening the connection bolt at 5–7 Nm. Following connection, bleed the brakes using Shimano’s one-way bleed method to remove air bubbles and maintain lever feel. Always use Shimano mineral oil and a compatible bleed funnel to avoid cross-contamination.
During bleeding, gently pull the lever to check for sponginess. A properly bled system will have firm lever response with minimal free stroke. If necessary, repeat the bleed process until no air escapes from the caliper.
Adjustment and Lever Reach Customization
The ST‑RX820 Di2 levers include reach adjustment to accommodate different hand sizes. Using a 2 mm hex wrench, adjust the reach screw located under the rubber hood. This allows fine-tuning of lever distance, making the braking action more ergonomic and reducing fatigue on long rides.
Free stroke adjustment can also be performed via the small set screw near the master cylinder, allowing users to modify when brake pad engagement occurs in the lever pull arc.
Firmware Integration and System Setup
Once installed, the brake set should be synced via Shimano’s E-Tube Project app. Connect via Bluetooth or USB to update firmware and customize shift mapping. The ST‑RX820 Di2 supports multi-shift options, button reassignment, and shift speed adjustments. These parameters can enhance rider control, especially when paired with other 12-speed GRX Di2 components.
Routine Maintenance and Inspection
Regular checks are essential to maintain performance and safety. Inspect the hose for wear or kinks and replace if damage is noted. Check brake pad thickness; pads should be replaced if below 1.0 mm. Clean the calipers with isopropyl alcohol, avoiding contact with rotors to prevent contamination.
Hydraulic fluid should be flushed at least once per year or after heavy use in muddy or wet conditions. Monitor lever feel over time, as sponginess indicates air ingress or fluid degradation.
Troubleshooting Common Issues
Some common issues include:
- Soft Lever Feel: Likely due to air in the hydraulic line. Bleed the brakes thoroughly.
- Inconsistent Braking Power: Could result from contaminated pads or rotors. Clean or replace as needed.
- Lever Rattle or Free Play: Check torque on mounting bolts and inspect pivot pins for wear.
- Shift Buttons Unresponsive: Verify battery charge, inspect E-Tube connections, and update firmware.
Use Shimano’s diagnostic mode within the E-Tube Project to test button function and identify faulty connections.
Performance Optimization Tips
Riders can fine-tune their braking performance by experimenting with pad compounds. For example, metallic pads offer longer life and better heat resistance, whereas resin pads provide quieter, more responsive braking. Similarly, larger rotors (160 mm or 180 mm) can enhance braking force for heavier riders or technical descents.
Ergonomic tweaks such as inward lever tilt or customized button remapping can significantly improve control during challenging terrain transitions.
Compatibility with Other Components
The GRX ST‑RX820 Di2 is fully compatible with Shimano’s 12-speed GRX Di2 drivetrains and is backward-compatible with many Ultegra and Dura-Ace Di2 components, assuming firmware parity and correct Di2 wiring. Hydraulic braking compatibility requires use of Shimano’s road/gravel-specific flat-mount calipers (BR-RX820 or BR-RX610).
Care must be taken when integrating third-party handlebars or stems, as the semi-internal Di2 routing may not suit all designs. Always test fit and check wire clearance before finalizing cockpit assembly.
Comparison with Similar Brake Systems
Compared to Shimano’s Ultegra ST-R8170 Di2, the GRX ST‑RX820 Di2 has distinct gravel ergonomics with textured hoods and a more aggressive lever flare for control over bumpy terrain. While both use the same wireless electronic shifting protocol, the GRX lever is optimized for varied grip positions and off-road responsiveness.
In contrast, SRAM’s Rival eTap AXS also offers wireless gravel braking and shifting, but uses a different button layout and DOT fluid rather than mineral oil. Riders who prefer minimal maintenance and a lighter feel may lean toward Shimano’s offering.
FAQs
1. Can I use the GRX ST‑RX820 Di2 levers with mountain bike calipers?
No, these levers are designed for road/gravel flat-mount calipers. MTB calipers use a different fluid volume and lever ratio.
2. How often should I bleed the GRX ST‑RX820 Di2 brakes?
Shimano recommends bleeding once a year or every 6,000 km, depending on riding conditions.
3. Are the Di2 wires in the ST‑RX820 fully wireless?
The system uses wireless shifters and a wired connection to the battery. There is still internal wiring between components for power distribution.
4. Can I adjust the shifting buttons on the brake levers?
Yes, customization is available through the E-Tube Project app, including multi-shift, reassignment, and shift delay settings.
5. Is this system compatible with mechanical GRX components?
No, GRX ST‑RX820 Di2 is an electronic-only system and must be paired with compatible Di2 derailleurs and drivetrain components.
6. Does this brake set work with older 11-speed Di2 systems?
No, it is designed for Shimano’s 12-speed Di2 ecosystem and will not interface correctly with 11-speed firmware or drivetrain parts.