The Shimano SM-EW90-B [paid link] Junction Box is one of the most widely used connection interfaces in Shimano’s Di2 electronic shifting systems. As electronic drivetrains evolve, riders often wonder whether upgrading the SM-EW90-B [paid link] is possible—or even necessary—to achieve modern performance and connectivity. This detailed guide explores upgrade paths, compatibility with current and legacy components, and the best practices for optimizing your Di2 setup using the SM-EW90-B.
Understanding the Shimano SM-EW90-B
The Shimano SM-EW90-B is a 3-port Di2 junction box designed to connect the shifters and the main wiring harness in Shimano’s electronic groupsets. It acts as the central communication hub for the rider’s control inputs and the derailleurs’ electronic responses.
Unlike the smaller SM-EW90-A [paid link] (2-port) version, the SM-EW90-B provides an additional port, allowing for more complex setups such as dual shifters or auxiliary climbing switches. It’s typically mounted under the stem for easy access and features a charging and adjustment port used for firmware updates and diagnostics.
Upgrading the SM-EW90-B: Is It Necessary?
In most cases, upgrading the SM-EW90-B is not strictly required unless you are transitioning to newer Di2 systems that use a different communication protocol. Shimano’s Di2 platforms can be categorized into two generations:
- First and Second Generation (E-Tube 2 systems) – Includes 10-speed and 11-speed Di2 components such as Dura-Ace 9070, Ultegra 6870, and early XT/XTR Di2.
- Current Generation (E-Tube 3 systems) – Includes 12-speed Di2 systems like Dura-Ace R9200, Ultegra R8100, and 105 R7100.
The SM-EW90-B is fully compatible with E-Tube 2 systems but not with E-Tube 3. Therefore, upgrading to a 12-speed Di2 drivetrain requires replacing the SM-EW90-B with the newer EW-RS910 [paid link] bar-end junction or EW-JC304 inline junctions.
If you are maintaining or slightly updating an 11-speed Di2 setup, the SM-EW90-B remains perfectly functional and does not hinder performance or reliability.
Compatibility Overview
Compatibility is the most critical factor when considering upgrades. The SM-EW90-B operates on the E-Tube 2 protocol, meaning it communicates only with components that support the same system version. Below is a simplified compatibility reference:
| Component Type | Compatible with SM-EW90-B | Notes |
|---|---|---|
| Dura-Ace 9070 Di2 | ✅ Yes | Full compatibility |
| Ultegra 6870 Di2 | ✅ Yes | Full compatibility |
| XT/XTR Di2 (M8050/M9050) | ✅ Yes | Compatible for MTB setups |
| Dura-Ace R9150/R8050 | ✅ Yes | Works with firmware updates |
| Dura-Ace R9200/R8100 | ❌ No | E-Tube 3 protocol only |
| 105 R7100 Di2 | ❌ No | Not supported |
| EW-RS910 [paid link] | ⚠️ Limited | Only with correct internal wiring |
| Wireless Unit EW-WU111 | ✅ Yes | Adds Bluetooth functionality |
For partial upgrades—such as adding wireless communication or integrating newer shifters—the EW-WU111 wireless unit can be connected to the existing SM-EW90-B system without replacing the junction box.
Best Practices for Upgrading
When planning an upgrade involving the SM-EW90-B, follow these best practices to ensure compatibility and performance stability:
1. Verify Firmware Versions
Before integrating any new component, connect your system to the Shimano E-Tube Project software. Update all devices to the latest firmware to ensure smooth communication between components. Mismatched firmware is one of the leading causes of Di2 malfunction.
2. Maintain Correct Cable Configuration
The SM-EW90-B uses standard E-Tube wires (EW-SD50). If you’re introducing newer components like the EW-WU111 or replacing shifters, check that the total cable length and routing conform to Shimano’s voltage stability guidelines. Avoid connecting more than five junction points in series.
3. Upgrade the Battery for Better Integration
If you’re currently using an older external battery (SM-BTR1), consider upgrading to the internal SM-BTR2 or BT-DN110 battery. These models enable wireless connectivity and synchronization with head units via ANT+ and Bluetooth when paired with the SM-EW90-B.
4. Add Wireless Connectivity
Integrating the EW-WU111 or EW-WU101 wireless module is the simplest way to modernize your Di2 setup without replacing the SM-EW90-B. It allows you to connect your Di2 system to head units, display gear data, and perform wireless firmware updates.
5. Replace Damaged Ports
Over time, frequent cable insertion and removal can wear the junction’s ports. If a port becomes loose or unreliable, replacement of the SM-EW90-B is the only solution. Always inspect connectors for corrosion or frayed insulation during maintenance.
When Replacement Becomes Necessary
You should replace the SM-EW90-B under the following conditions:
- Transitioning to a 12-speed Di2 system (R9200/R8100/R7100).
- Adding internal bar-end junctions (EW-RS910) with fully internal wiring.
- Experiencing intermittent communication loss or failure to charge.
- Dealing with physically damaged or corroded ports.
In such cases, replacing the SM-EW90-B with a newer generation junction provides more stable connectivity, compact design, and direct frame integration options.
Optimizing Performance After Upgrading
After upgrading or maintaining your SM-EW90-B, always perform a system diagnostic test using Shimano’s E-Tube Project software. Confirm that each shifter, derailleur, and junction responds correctly. Then recalibrate the derailleurs for precise shifting. Regular firmware checks ensure long-term reliability and prevent communication errors.
For optimal performance, inspect cable connections monthly, especially in wet or high-vibration environments. Keeping connectors clean and lubricated with Shimano’s E-Tube grease prevents corrosion and signal degradation.
Comparison with Newer Junction Options
| Junction Model | Ports | Mount Type | System Compatibility | Wireless Ready |
|---|---|---|---|---|
| SM-EW90-B | 3 | External | E-Tube 2 | With EW-WU111 |
| SM-EW90-A [paid link] | 2 | External | E-Tube 2 | With EW-WU111 |
| EW-RS910 | 2 | Internal (bar-end) | E-Tube 2/3 | Yes |
| EW-JC304 | 4 | Inline (frame) | E-Tube 3 | Yes |
The EW-RS910 and EW-JC304 are modern replacements designed for cleaner aesthetics and improved cable management. However, for riders using 11-speed Di2 systems, the SM-EW90-B remains a practical and fully supported choice.
Conclusion
The Shimano SM-EW90-B continues to serve as a reliable and high-performing junction option for 11-speed Di2 users. While it cannot be directly upgraded to function with 12-speed E-Tube 3 systems, it remains compatible with a wide range of modern accessories, including wireless units and internal batteries.
Upgrading around the SM-EW90-B—rather than replacing it—often provides the best balance of cost, performance, and compatibility. For cyclists maintaining or modernizing their Di2 setup, understanding these upgrade paths ensures seamless operation and long-term reliability of the entire drivetrain.