Can You Upgrade Your SM-EW90-A? Compatibility and Best Practices

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The Shimano SM-EW90-A [paid link] Junction A is a key component in Shimano’s Di2 (Digital Integrated Intelligence) electronic shifting system. Acting as the interface between the rider and the drivetrain, it connects the shifters, battery, and derailleurs through the Di2 E-Tube network. As Di2 technology continues to evolve, many cyclists consider upgrading or integrating newer components with the SM-EW90-A [paid link]. This guide explains everything you need to know about upgrading your SM-EW90-A, including compatibility rules, common issues, and the best upgrade practices to ensure flawless system performance.

Understanding the SM-EW90-A

The SM-EW90-A serves as the front junction box (Junction A) in Shimano’s older Di2 E-Tube systems. It provides connection ports for shifters and the internal battery wiring, enabling communication across the entire Di2 system. Typically mounted under the stem, it also serves as the charging and adjustment access point.

This model features three E-Tube ports, making it ideal for setups with standard dual-control road shifters. It operates as part of Shimano’s E-Tube system, which allows firmware updates and component customization through the E-Tube Project software.

Compatibility Overview

Before upgrading or replacing any Di2 component, it’s crucial to confirm E-Tube compatibility. The SM-EW90-A is compatible with E-Tube systems that use SD50 connectors, including:

  • Shimano Ultegra Di2 6770 and 6870
  • Shimano Dura-Ace Di2 9070
  • Shimano XT Di2 M8050 and XTR Di2 M9050 (with correct wiring)

It is not compatible with newer systems using SD300 connectors, such as:

  • Shimano Ultegra R8100 Di2
  • Shimano Dura-Ace R9200 Di2
  • Shimano 105 Di2 R7100

These newer models rely on 12-speed E-Tube SD300 wiring, which is smaller and incompatible with the SM-EW90-A’s SD50 ports.

Upgrading from SM-EW90-A to Newer Junction Options

Shimano has gradually moved away from external junction boxes in its latest Di2 systems. If you’re considering upgrading, there are a few paths available depending on your goals and drivetrain generation.

Upgrading Within the Same E-Tube Generation (SD50 System)

If you want to maintain SD50 compatibility, consider replacing the SM-EW90-A with the SM-EW90-B [paid link], which offers five E-Tube ports instead of three. This is ideal if you plan to add accessories like sprint shifters or satellite shifters.

The system wiring and connections remain identical, meaning no firmware or wiring changes are necessary—simply replace the junction box and reprogram the system using Shimano E-Tube Project software.

Upgrading to a Newer E-Tube SD300 System

If you intend to move to a 12-speed Di2 system, such as Dura-Ace R9200 or Ultegra R8100, you will need to replace:

  • The SM-EW90-A with EW-RS910 [paid link] (bar-end or frame-integrated junction)
  • All E-Tube SD50 wires with SD300 wires
  • The battery (BT-DN110) if upgrading from an older internal or external model
  • The derailleurs and shifters, since they are not backward compatible

This type of upgrade essentially transforms your entire Di2 setup into the latest standard, improving performance and reducing wiring complexity.

Mixing SM-EW90-A with Other Components

The SM-EW90-A can still be used effectively in hybrid setups as long as E-Tube SD50 connectors are maintained across the system. It works seamlessly with:

  • Junction B (SM-JC41 [paid link])
  • Internal Battery (BT-DN110)
  • Wireless Units (EW-WU111 or EW-WU101) for Bluetooth connectivity

However, caution should be taken when mixing firmware versions. Always ensure that all connected components are updated to the latest firmware using the E-Tube Project app to prevent communication errors.

Firmware and E-Tube Project Considerations

Firmware compatibility plays a crucial role in determining whether your SM-EW90-A can function properly within a mixed system. Shimano’s E-Tube Project software for Windows or mobile devices allows:

  • Firmware updates
  • Button function customization
  • Diagnostics for error codes and connection issues

If your SM-EW90-A fails to connect during updates, ensure it’s powered via a compatible internal battery (BT-DN110) or external charger (SM-BCR2). Always use genuine Shimano cables during the update process to avoid data errors.

Common Compatibility Issues

Cyclists attempting partial upgrades often encounter communication failures or unresponsive components. These are usually caused by:

  • Mismatched firmware versions between SD50 and SD300 systems
  • Incorrect cable types (mixing SD50 and SD300 without adapters)
  • Unsupported component pairing, such as connecting R8100 shifters to SM-EW90-A
  • Outdated firmware that prevents Bluetooth modules from syncing

To prevent these issues, confirm full system compatibility using Shimano’s official E-Tube compatibility chart before beginning any upgrade.

Best Practices for a Smooth Upgrade

When upgrading your Di2 system, precision and planning ensure reliable operation and long-term performance. Follow these best practices:

  • Use only Shimano-approved E-Tube wires and connectors.
  • Keep all firmware updated before integrating new components.
  • Avoid mixing SD50 and SD300 wiring standards.
  • Check battery compatibility—older SM-BTR2 batteries may not support advanced features.
  • Test the system using E-Tube diagnostics before road testing.

A properly executed upgrade preserves the SM-EW90-A’s functionality and extends the life of your Di2 setup.

Alternatives and Future-Proofing

If your primary goal is future-proofing, consider migrating entirely to the EW-RS910 [paid link] junction with SD300 wiring. Although it requires a full conversion, it offers a cleaner cockpit and better integration with modern frames.

However, for riders using 10- or 11-speed Di2 systems, maintaining the SM-EW90-A remains cost-effective and efficient. Its reliability, serviceability, and compatibility with legacy systems make it a strong choice for continued use.

Conclusion

Upgrading the Shimano SM-EW90-A depends largely on your drivetrain generation and wiring standard. While it remains fully viable within 10- and 11-speed Di2 systems, it cannot integrate directly with the latest 12-speed SD300-based drivetrains. For those staying within the same E-Tube generation, upgrading to the SM-EW90-B [paid link] or adding wireless units provides improved functionality without replacing the entire system.

By following best practices, maintaining firmware consistency, and verifying compatibility, you can confidently enhance your Di2 setup for years of reliable shifting performance.