Expert Opinions: GRX RD-RX820 Rear Derailleurs Reviewed

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The Shimano GRX RD-RX820 [paid link] rear derailleur is a high-performance component designed specifically for gravel and adventure cycling. This model is part of Shimano’s GRX series, which is tailored to meet the demanding conditions of gravel and off-road riding. In this guide, we will cover the installation, adjustment, maintenance, troubleshooting, and customization of the GRX RD-RX820, ensuring riders can achieve optimal performance. We will also compare this model with others in Shimano’s GRX lineup to help cyclists make informed decisions.

Installation of the Shimano GRX RD-RX820 Rear Derailleur

Proper installation is crucial for the GRX RD-RX820 rear derailleur to function effectively. Follow these steps carefully to ensure that it is mounted correctly.

Tools Required:

  • 5mm Allen wrench
  • 3mm Allen wrench
  • Chain tool
  • Screwdriver (for barrel adjuster)
  • Torque wrench
  • Shimano-compatible chain
  • Appropriate rear wheel with a compatible freehub body

Installation Steps:

  1. Remove the Existing Rear Derailleur:
    If you’re replacing an old derailleur, first remove the rear wheel and detach the chain. Use the 5mm Allen wrench to loosen and remove the derailleur hanger bolt.
  2. Install the Derailleur Hanger (if needed):
    Ensure the derailleur hanger is properly aligned with the frame. If necessary, install a new hanger to provide a stable base for the RD-RX820.
  3. Attach the Derailleur:
    Position the GRX RD-RX820 derailleur onto the derailleur hanger and secure it with the 5mm Allen wrench. Tighten the bolt to the manufacturer’s recommended torque specification.
  4. Set the Chain Length:
    Check your chain length. Use a chain tool to size the chain appropriately for your drivetrain. The GRX RD-RX820 supports both 10-speed and 11-speed chains, so ensure compatibility.
  5. Install the Chain on the Derailleur:
    Thread the chain through the jockey wheels of the derailleur, following the correct chain path. Ensure that the chain is properly routed through the front and rear derailleur pulleys.
  6. Attach the Rear Wheel:
    Once the derailleur and chain are in place, reinstall the rear wheel and make sure the freehub body is correctly engaged.
  7. Cable Installation:
    Install the derailleur cable into the derailleur’s cable anchor bolt and tighten it with a 3mm Allen wrench. Adjust the barrel adjuster at the derailleur to ensure smooth shifting.
  8. Final Check:
    After the derailleur is mounted, check the alignment and ensure that the derailleur moves freely without obstruction. Ensure the shifting is responsive before riding.

Adjustment of the Shimano GRX RD-RX820 Rear Derailleur

Fine-tuning the GRX RD-RX820 rear derailleur is essential for smooth shifting performance. Follow these steps to adjust the derailleur:

Limit Screw Adjustments:

  1. High Gear Limit Screw:
    • Shift the chain to the smallest cog at the rear cassette.
    • Use a screwdriver to adjust the high limit screw so that the derailleur’s jockey wheel aligns with the smallest cog. This will prevent the derailleur from overshooting and causing chain drop.
  2. Low Gear Limit Screw:
    • Shift the chain to the largest cog at the rear.
    • Adjust the low limit screw so that the derailleur’s jockey wheel aligns with the largest cog. This prevents the derailleur from shifting past the largest cog.

B-Tension Screw Adjustment:

  • The B-tension screw controls the derailleur’s distance from the cassette. Adjust this screw to fine-tune the jockey wheel position. The recommended distance between the jockey wheel and the largest cog is about 6–8mm.
  • A properly adjusted B-tension screw helps prevent chain skipping and optimizes shifting precision.

Shifting Precision:

  • Shift through the gears while adjusting the barrel adjuster located on the derailleur. This will help fine-tune the tension of the derailleur cable, ensuring smooth shifting between gears.
  • If shifts are hesitant or inaccurate, the barrel adjuster may need further fine-tuning.

Maintenance of the Shimano GRX RD-RX820 Rear Derailleur

Routine maintenance is key to ensuring the longevity and performance of your Shimano GRX RD-RX820. Below are the maintenance tips:

Cleaning and Lubing:

  1. Regular Cleaning:
    Clean the derailleur after every ride, especially after riding on gravel or in muddy conditions. Use a soft brush and mild detergent to remove dirt, sand, and debris. Avoid harsh chemicals that may damage the derailleur’s finish.
  2. Lubing the Jockey Wheels:
    Apply a small amount of lubricant to the jockey wheels every few rides to reduce friction and ensure smooth movement.

Cable Inspection and Replacement:

  1. Inspect Cables Regularly:
    Check the derailleur cable for fraying or signs of wear. Replace the cable if necessary to maintain smooth shifting.
  2. Lubricate the Cable:
    Apply lubrication to the derailleur cable before installation to ensure smooth movement and reduce friction.

Inspecting the Derailleur Hanger:

  • Periodically check the derailleur hanger for any bending or damage. A misaligned hanger can cause shifting issues. If the hanger is bent, carefully straighten it with a derailleur hanger alignment tool, or replace it if necessary.

Chain Wear:

  • Regularly check the wear on your chain. A worn-out chain can cause poor shifting performance. Replace the chain when necessary, especially if the drivetrain feels sluggish or if there is skipping between gears.

Troubleshooting Common Issues with the GRX RD-RX820 Rear Derailleur

Several issues can affect the performance of the Shimano GRX RD-RX820 rear derailleur. Here are common problems and their solutions:

  1. Chain Skipping or Hesitant Shifting:
    • Cause: Likely caused by a worn-out chain or derailleur cable.
    • Solution: Replace the chain and lubricate or replace the derailleur cable.
  2. Shifting Between Gears is Slow:
    • Cause: Poorly adjusted barrel adjuster or stretched derailleur cable.
    • Solution: Fine-tune the barrel adjuster for smoother shifting, or replace the derailleur cable if necessary.
  3. Derailleur Jumps Off the Cassette:
    • Cause: Incorrect limit screw settings or a misaligned derailleur hanger.
    • Solution: Adjust the limit screws and check the derailleur hanger alignment.
  4. Chain Drops or Sprockets Don’t Shift Properly:
    • Cause: B-tension screw misadjustment or poor cable tension.
    • Solution: Adjust the B-tension screw and ensure proper cable tension.

Customization and Optimization for Better Performance

The Shimano GRX RD-RX820 rear derailleur is versatile and can be customized to suit a rider’s preferences. Here are a few optimization tips:

  1. Gear Ratio Adjustments:
    • Depending on the terrain, you may want to adjust the gearing on your bike to provide a better range of gears. Consider swapping out your cassette for a larger or smaller cog set to fine-tune your gear ratios for climbing or flat terrain.
  2. Derailleur Hanger Choice:
    • For added durability on rough terrains, opt for a stronger derailleur hanger made from materials like aluminum or steel. These hangers will be more resilient to impacts from rocks or gravel.
  3. Use of a Clutch Mechanism:
    • The RD-RX820 features Shimano’s clutch technology, which helps reduce chain slap. For extra stability in rough conditions, ensure the clutch is properly engaged by adjusting the derailleur tension. This will help maintain chain stability and reduce noise.

Comparison with Other Shimano GRX Models

Shimano offers several options within its GRX line, and the RD-RX820 stands out for gravel-focused riders. Here’s how it compares with other models:

  • Shimano GRX RD-RX810 [paid link]:
    The RD-RX810 is a more budget-friendly option than the RD-RX820, featuring fewer advanced features. It lacks the advanced clutch mechanism found in the RD-RX820 and is best suited for less aggressive off-road riding.
  • Shimano GRX RD-RX815:
    The RD-RX815 offers a similar clutch mechanism as the RD-RX820, but it features additional optimization for electronic shifting. It’s ideal for riders looking for an integrated electronic drivetrain but comes at a higher price point.

Compatibility with Other Drivetrain Components

The Shimano GRX RD-RX820 rear derailleur is designed for compatibility with Shimano’s 11-speed road and gravel cassettes. It works seamlessly with Shimano GRX shifters, and it’s advisable to pair the RD-RX820 with a GRX-specific front derailleur for optimal performance. However, it’s important to ensure the rear derailleur is paired with compatible chainrings, cranks, and cassette ratios to ensure smooth operation.