The SRAM RED eTap AXS D2 HRD [paid link] brake system represents the pinnacle of integrated wireless shifting and hydraulic braking. Designed with gravel and endurance riding in mind, it delivers precise control, low-maintenance performance, and seamless integration with SRAM’s AXS wireless ecosystem. This detailed guide walks you through the full process of installing, adjusting, and optimizing the RED eTap AXS D2 HRD brake set for your gravel bike.
Tools Required
- 5mm and 4mm hex wrenches
- T25 Torx wrench
- Hydraulic hose cutter
- SRAM Pro Bleed Kit
- DOT 4 brake fluid (only use DOT fluid; mineral oil is incompatible)
- Torque wrench with Nm scale
- Isopropyl alcohol and clean lint-free cloth
- Bleed block
- Safety glasses and nitrile gloves
System Overview
The RED eTap AXS D2 HRD combines electronic shifting via eTap with fully hydraulic disc braking. The levers serve as both shifters and hydraulic brake actuators. The setup includes:
- Wireless shift levers (left and right)
- Flat-mount hydraulic calipers
- Pre-bled hydraulic hoses (may require trimming)
- Bleed port on caliper and lever
- Compatibility with 12-speed AXS derailleurs and AXS app integration
This system is specifically optimized for modern gravel bikes with internal cable routing and flat-mount disc brakes.
Pre-Installation Preparation
Before starting, verify that your frame and fork are compatible with flat-mount disc calipers and that you have SRAM Centerline or compatible rotors already installed. Check if the frameset allows full internal routing of the hydraulic hose.
Ensure all components, including hoses, are new or recently cleaned. Any contamination can affect braking performance or damage components.
Lever and Caliper Installation
Handlebar and Lever Positioning:
Install the levers on the handlebars using a 4mm hex wrench. Position them ergonomically based on hand size and rider preference. Tighten to 6 Nm using a torque wrench. Do not over-tighten, as this could damage the carbon body.
Rear Brake Hose Routing:
Route the rear brake hose through the downtube and chainstay. Use internal routing guides or magnets if needed. Avoid sharp bends or kinks to maintain smooth hydraulic flow.
Trimming Brake Hose:
If the hose is too long, use a proper hydraulic hose cutter. Install a new hose barb and compression olive using a dedicated hose press tool. Torque the compression nut to 6-8 Nm.
Caliper Mounting:
Attach the caliper to the frame using T25 Torx bolts. For flat-mount standards, use appropriate spacers depending on rotor size. Torque bolts to 8-10 Nm. Ensure the brake pads are installed and the bleed block is inserted before proceeding.
Bleeding the Hydraulic Brake System
After hose trimming or re-installation, a brake bleed is mandatory to ensure no air is trapped.
- Attach bleed syringes to both lever and caliper bleed ports using SRAM’s bleed fittings.
- Fill one syringe with DOT 4 fluid, leaving the other empty.
- Slowly push fluid from caliper to lever, removing bubbles and air gaps.
- Reverse bleed fluid to ensure full purge.
- Tighten bleed port screws and remove syringes carefully to avoid fluid drips.
- Clean with isopropyl alcohol to eliminate residual fluid.
- Reinstall pads and ensure the rotor is free from contaminants.
Wireless Shifting Integration
Once brake hardware is installed:
- Pair levers with the AXS app and connect them to the derailleur.
- Confirm that firmware is up to date.
- Customize shift functions if needed using the app’s interface.
Ensure all pairing lights blink consistently. Test shifting without the chain first to verify operation.
Initial Adjustments
Lever Reach Adjustment:
Use the 2.5mm hex on the inside of the brake lever body to fine-tune reach for comfort.
Pad Contact Point:
Use the contact point adjustment dial to regulate the bite point. Set it for early engagement for technical gravel descents or longer travel for modulation.
Caliper Alignment:
Loosen mounting bolts slightly, squeeze the brake lever, then tighten bolts. This centers the caliper over the rotor.
Rotor Clearance:
Ensure the rotor spins freely without rubbing. Re-check alignment if scraping is heard.
Common Troubleshooting Issues
Soft Lever Feel:
Likely due to air in the system. Re-bleed both caliper and lever.
Rotor Rub:
Usually a result of improper caliper alignment or a bent rotor. Realign the caliper or true the rotor.
Unresponsive Shifting:
Check lever batteries and confirm AXS pairing. Update firmware if necessary.
Lever Rattle:
Ensure the clamp bolts are torqued correctly and that the lever body isn’t in contact with other cockpit components.
Performance Optimization
Brake Pad Selection:
For gravel use, consider semi-metallic pads for a balance of power and noise control. Organic pads wear faster but are quieter.
Rotor Size Upgrade:
Going from 140mm to 160mm rotors can significantly improve braking power for loaded bikepacking.
Lever Ergonomics:
Angle levers downward slightly to reduce wrist strain during long descents. Add textured bar tape for better grip with gloves.
Wireless Signal Clarity:
Keep AXS batteries charged and avoid overlapping channels from other wireless devices in crowded events.
Compatibility and Integration
The RED eTap AXS D2 HRD is compatible only with other AXS components. It will not function with mechanical drivetrains or SRAM’s earlier eTap 11-speed models.
Compatible components include:
- RED AXS front and rear derailleurs
- SRAM AXS power meters
- Force and Rival AXS components (mixed builds possible but may affect weight and aesthetics)
- SRAM Centerline X or CL rotors (160mm or 140mm options)
It uses the standard 12-speed Flattop chain and XDR freehub.
Comparison with Other Models
RED eTap AXS D1 HRD vs. D2 HRD:
The D2 model improves ergonomics, with redesigned lever shaping for gravel positioning. It also features enhanced bleed ports for easier service.
Force AXS HRD vs. RED eTap AXS D2 HRD:
While Force AXS offers similar functionality, RED has lighter materials, carbon levers, and titanium hardware—ideal for competitive or weight-focused riders.
Rival AXS HRD vs. RED eTap AXS D2 HRD:
Rival is budget-friendly with mostly steel hardware and fewer adjustments. RED is a better option for performance-tuned gravel bikes.
FAQs
Can I install RED eTap AXS D2 HRD levers with my older AXS derailleurs?
Yes, as long as they are part of the 12-speed AXS system, cross-compatibility is supported.
How often should I bleed the brakes?
For gravel riding, bleed annually or after 100 hours of riding. Bleed immediately after a hose trim or contamination.
Is the brake hose length the same for all bikes?
No, hoses are shipped long and must be trimmed to each frame’s routing requirements.
Can I use mineral oil instead of DOT fluid?
No. DOT 4 fluid is mandatory. Using mineral oil will destroy internal seals.
What’s the maximum rotor size supported?
Typically, 160mm rotors front and rear, but some frames may allow 180mm with the correct adapter.
Are lever adjustments tool-free?
No. Reach and contact point adjustments require a hex key, but can be done without removing components.
Conclusion
Installing and optimizing the SRAM RED eTap AXS D2 HRD brake set transforms your gravel bike into a high-performance, race-ready machine. While setup demands attention to detail, the reward is a fully wireless cockpit with precise shifting and confident braking. By following this guide and performing regular maintenance, you’ll ensure smooth, reliable operation across rugged terrain.