How to Install, Adjust, and Maintain the RD-RX805 Rear Derailleur

Posted on
in Di2, Rear Derailleur, Shimano

The Shimano RD-RX805 [paid link] rear derailleur is a high-performance, electronic shifting component designed for gravel and road bikes using Shimano’s Di2 electronic drivetrain. It features a Shadow RD+ clutch to reduce chain slap and improve chain retention, making it a great option for mixed-terrain riding. Proper installation, adjustment, and maintenance are crucial to ensure smooth and precise shifting.

This guide will walk you through step-by-step installation, fine-tuning adjustments, and routine maintenance to keep your RD-RX805 [paid link] derailleur performing flawlessly.

Tools Required [paid links]

Before beginning, ensure you have the following tools:

RD-RX805 Rear Derailleur Installation Guide

Step 1: Prepare Your Bike

  1. Shift the chain onto the smallest chainring and smallest rear cog to reduce tension.
  2. Remove the old derailleur (if replacing) by loosening the mounting bolt with a 5mm Allen wrench [paid link].
  3. Clean the derailleur hanger with a degreaser and inspect for bends or misalignment.

Step 2: Attach the RD-RX805 to the Derailleur Hanger

  1. Align the mounting bolt with the derailleur hanger threads.
  2. Tighten the bolt to 8-10Nm using a torque wrench [paid link].
  3. Ensure the derailleur is firmly secured and sits in the correct position.

Step 3: Connect the Di2 Wiring

  1. Plug in the EW-SD50 electronic wire to the derailleur.
  2. Route the wire neatly along the frame and connect it to the Di2 junction box.
  3. Secure the wire using cable guides or adhesive mounts to prevent movement.

Step 4: Adjust the B-Tension Screw

  1. Shift the derailleur to the largest rear cog.
  2. Adjust the B-tension screw using a 2mm Allen wrench [paid link] to ensure the jockey wheel sits 5-6mm from the cassette.
  3. This adjustment optimizes chain wrap and shifting performance.

Step 5: Perform Initial Electronic Setup

  1. Use the Shimano E-Tube Project app to check for firmware updates.
  2. Calibrate the derailleur by holding the Di2 shift button until the LED blinks.
  3. Run a test shift sequence through all gears to confirm proper function.

Fine-Tuning the RD-RX805 for Optimal Shifting Performance

Adjusting Indexing for Smooth Shifting

  1. Use the Di2 micro-adjust mode by pressing and holding the junction box button until the LED blinks red.
  2. Tap the shift buttons to make fine adjustments in 0.2mm increments.
  3. Shift through all gears and listen for chain noise or hesitation.

Limit Screw Adjustments for Proper Gear Range

  1. Shift to the smallest rear cog and adjust the H-limit screw until the derailleur aligns with the cog.
  2. Shift to the largest rear cog and adjust the L-limit screw to prevent overshifting into the spokes.

Clutch Activation for Rough Terrain

  1. Engage the Shadow RD+ clutch using the lever on the derailleur.
  2. This feature reduces chain slap and improves chain stability on rough terrain.
  3. Disengage the clutch when removing the rear wheel for easier handling.

RD-RX805 Rear Derailleur Maintenance Tips

Cleaning and Lubrication

  1. Use a mild degreaser and a soft brush to clean the derailleur.
  2. Avoid spraying water directly into electronic ports or pivots.
  3. Apply a light lubricant to the jockey wheels and pivot points.

Checking for Wear and Damage

  1. Inspect the jockey wheels for excessive wear and replace if necessary.
  2. Check the Di2 wiring for loose connections or damage.
  3. Use a chain checker tool to monitor chain wear and replace at 0.5% elongation.

Updating Firmware for Best Performance

  1. Connect the derailleur to the Shimano E-Tube software via a PC or smartphone.
  2. Check for firmware updates to ensure compatibility with the latest components.
  3. Perform a derailleur reset if shifting issues arise.

Troubleshooting Common RD-RX805 Issues

1. Slow or Inconsistent Shifting

  • Ensure the Di2 battery is fully charged.
  • Check for bent derailleur hangers using a hanger alignment tool.
  • Recalibrate the derailleur using Di2 micro-adjust mode.

2. Chain Slap or Excessive Noise

  • Activate the clutch mechanism to reduce chain movement.
  • Ensure the B-tension screw is set properly for optimal chain wrap.

3. Unexpected Shifting Behavior

  • Inspect the Di2 wiring connections and reconnect if loose.
  • Update the firmware using Shimano E-Tube software.

Comparing the RD-RX805 with Other Shimano Rear Derailleurs

The Shimano RD-RX805 [paid link] stands out due to its Di2 electronic shifting and Shadow RD+ clutch. Here’s how it compares to other models:

FeatureRD-RX805RD-R8050 [paid link] (Ultegra Di2)RD-RX817 (GRX Di2)
Electronic ShiftingYesYesYes
Clutch MechanismYes (Shadow RD+)NoYes (GRX Clutch)
Cassette Compatibility11-34T11-30T11-42T
Best UseRoad & GravelRoadGravel & Adventure

Final Thoughts

The Shimano RD-RX805 rear derailleur is a powerful, electronic shifting component designed for gravel and road cyclists who need precise, smooth shifting. Proper installation, fine-tuning, and regular maintenance will ensure it performs flawlessly for years.