The Shimano GRX RD-RX820 [paid link] rear derailleur is a highly specialized component designed specifically for gravel bikes. With its focus on durability, precision, and versatility, the RD-RX820 is engineered to provide a smooth and wide gear range that enhances performance on varied gravel terrain. Whether you’re climbing steep grades, navigating technical descents, or cruising across flat gravel roads, the GRX RD-RX820 ensures optimal shifting performance. This guide will cover the installation, adjustment, and maintenance of the RD-RX820, as well as troubleshooting common issues, customization for performance, and its compatibility with other drivetrain components.
Tools Required
- 5mm Allen wrench
- 3mm Allen wrench
- Shimano-compatible quick link or chain tool
- Torque wrench
- T25 Torx wrench
- Chain checker tool
- Cable cutters
- Cable tension tool
Installation of the GRX RD-RX820
Step 1: Mounting the Derailleur
Start by mounting the GRX RD-RX820 onto the derailleur hanger using the included mounting bolt. Tighten the bolt with a torque wrench to the manufacturer’s recommended torque setting, typically 8-10 Nm. Ensure that the derailleur is positioned properly and aligned with the rear cassette.
Step 2: Attaching the Chain
Feed the chain through the jockey wheels of the derailleur, ensuring that the chain is properly threaded through the rear derailleur cage. The chain should run smoothly and evenly through the derailleur’s path. Use a chain tool to remove or adjust the chain length to match the gearing setup.
Step 3: Connecting the Shift Cable
Once the derailleur is mounted and the chain is correctly placed, you can attach the shift cable to the derailleur. Start by routing the cable through the cable guide and securing it in the derailleur’s cable anchor. Tighten the anchor bolt using a 5mm Allen wrench.
Step 4: Setting Up the Shifter and Adjusting Cable Tension
Install the shifter on your handlebars, making sure it is positioned in a comfortable location for quick access. Once installed, route the cable from the shifter to the derailleur, ensuring it is not kinked. Adjust the cable tension so that it provides smooth shifting under load.
Adjusting the GRX RD-RX820 for Optimal Performance
Step 1: High and Low Limit Screws
The GRX RD-RX820 features two limit screws—one for the high gear (H) and one for the low gear (L). Begin by adjusting these screws to ensure the derailleur moves freely across the entire gear range without the chain overshooting the largest or smallest cog.
- High Limit (H): Adjust the H screw so that the derailleur shifts cleanly to the smallest cog without overshooting it.
- Low Limit (L): Adjust the L screw so that the derailleur moves to the largest cog smoothly without the chain falling off.
Step 2: Indexing the Gears
Once the limit screws are set, focus on indexing the gears. Using the barrel adjuster located on the derailleur or shifter, fine-tune the cable tension until the derailleur shifts smoothly across all gears. Each shift should feel crisp and immediate.
Step 3: Checking B-Screw Tension
The B-screw adjusts the distance between the derailleur and the cassette, affecting the derailleur’s ability to shift smoothly across all gears. Set the B-screw so that the derailleur’s upper jockey wheel sits at an appropriate distance from the largest cog, typically 5-6mm. This ensures that the derailleur can move freely without rubbing the cassette.
Maintenance of the GRX RD-RX820
Regular Cleaning and Lubing
The GRX RD-RX820 is built to handle harsh conditions, but regular maintenance will ensure it performs optimally for years. Clean the derailleur regularly by wiping it down with a soft cloth and removing any dirt or debris that may cause friction or poor shifting. Lubricate the pivot points and jockey wheels with a light oil to reduce wear and improve smoothness.
Checking Chain Wear
The condition of the chain is critical to the performance of the RD-RX820. Use a chain checker tool to regularly check for wear and replace the chain when necessary. A worn chain can cause skipping and poor shifting performance, especially in the larger cogs.
Inspecting Cable and Housing
Check the shift cables and housing periodically for any signs of fraying or wear. Replace the cables if they become stiff or damaged. A worn cable can lead to inconsistent shifting, especially when riding on rough gravel.
Troubleshooting Common Setup Issues
Issue 1: Chain Dropping Off the Largest or Smallest Cog
If the chain is falling off the largest or smallest cog, it’s likely due to improperly adjusted limit screws. Revisit the H and L screws and fine-tune them until the derailleur stops the chain from overshooting the cogs.
Issue 2: Poor Shifting Performance
If shifting feels sluggish or imprecise, check the cable tension. A loose or overtightened cable can cause delayed or skipped shifts. Use the barrel adjuster to fine-tune the tension for smoother shifting.
Issue 3: Jockey Wheel Rubbing on the Cassette
If the derailleur cage is rubbing against the cassette, check the B-screw tension. If the gap between the derailleur and the cassette is too tight, adjust the B-screw to create more clearance.
Customization for Better Performance
Optimizing Gear Range for Gravel Riding
One of the main features of the GRX RD-RX820 is its extended gear range, making it ideal for gravel biking. The RD-RX820 supports wide-range cassettes, allowing you to tackle steep climbs and fast descents with ease. Riders can customize their gearing by choosing a wider-range cassette or pairing the derailleur with specific chainring sizes to suit their preferred terrain and riding style.
Upgrading to a Wide-Range Cassette
For gravel riders who often tackle steep, technical terrain, upgrading to a larger cassette (e.g., an 11-34T or 11-36T) can provide more climbing gears. The RD-RX820 accommodates these larger cassettes, making it an excellent choice for long, challenging rides.
Compatibility with Other Drivetrain Components
Shimano GRX and Other Drivetrain Systems
The GRX RD-RX820 is part of Shimano’s GRX gravel groupset, which is designed specifically for gravel bikes. It’s fully compatible with Shimano’s 11-speed road and gravel components, making it easy to integrate into existing Shimano drivetrain systems. However, it’s important to ensure that the shifters, chain, and cassette are all from the same Shimano 11-speed groupset for optimal performance.
Compatibility with Non-Shimano Components
While the GRX RD-RX820 works best with Shimano-specific components, it may be possible to pair it with non-Shimano components, such as different brand shifters or chains. However, this may require additional adjustments or specialized adapters, and shifting performance may not be as precise.