The Shimano SM-EW90 series is a central junction box that forms the interface between Di2 electronic shifting components and the rider’s cockpit. It acts as the communication hub for connecting shifters, derailleurs, and the main battery unit. While the SM-EW90-A [paid link] and SM-EW90-B [paid link] share the same fundamental purpose, several technical and practical differences set them apart. Understanding these distinctions helps ensure a proper setup and optimal performance for your electronic drivetrain.
Understanding the Purpose of the SM-EW90 Series
The SM-EW90 series was designed as a key component in Shimano’s E-Tube Di2 platform. It enables riders to connect their shifters, derailleurs, and junction points into a unified system, allowing for electronic shifting with customizable configurations. The junction box typically mounts under the stem or inside the handlebar area, depending on the frame design and integration preferences.
Both the SM-EW90-A [paid link] and SM-EW90-B [paid link] models act as cockpit junctions but differ in the number of available ports and potential integration options, influencing their use in different bike setups.
Design and Port Configuration
The most noticeable distinction between the two models lies in their port configuration. The SM-EW90-A features two E-Tube ports, while the SM-EW90-B includes three. This single port difference affects overall system layout and compatibility with specific handlebar configurations.
The SM-EW90-A is typically used on simpler setups—most commonly 2-port configurations such as single shifter integration for time trial or triathlon bikes. On the other hand, the SM-EW90-B is intended for road bike setups requiring multiple shifter connections, such as dual levers and an additional control switch.
For mechanics and riders setting up Di2 systems, this port difference determines which model is compatible with the intended handlebar layout. The SM-EW90-B’s third port allows more flexibility, especially in systems where auxiliary shifters or sprint buttons are desired.
Installation and Mounting Considerations
Both versions share similar installation steps. They mount under the stem or inside an integrated cockpit using Shimano’s rubber band mount or frame-specific adapters. However, the SM-EW90-B’s additional port requires more careful routing to prevent excess cable strain or crossing lines between shifters.
The SM-EW90-A offers a cleaner aesthetic for riders who prefer a minimal cable setup, especially when only two E-Tube connections are necessary. Conversely, the SM-EW90-B may require more cable management but provides greater versatility for those running multiple shifters or controls.
When installing either model, ensuring proper cable slack is crucial. Excess tension in the E-Tube cables can lead to intermittent connectivity or stress on the junction box ports. Always check alignment before tightening mounts, and avoid sharp bends that could compromise the cable integrity.
Compatibility with Di2 Systems
Both models are compatible with Shimano’s 11-speed Di2 systems, including Dura-Ace 9070, Ultegra 6870, and subsequent E-Tube-based generations. The key compatibility factor is the number of shifters being integrated, not the drivetrain level [paid link] itself.
The SM-EW90-A works best for setups requiring only two connections, such as:
- Time trial or triathlon bikes with bar-end shifters and no secondary controls.
- Minimal road setups where an external display or additional shifter is unnecessary.
The SM-EW90-B, with three ports, is recommended for:
- Road bikes with dual shifters (left and right) and an optional climbing or sprint shifter.
- Riders who plan to add satellite shifters or auxiliary buttons later.
Both units connect seamlessly to Shimano’s SM-EW67 or frame junctions via E-Tube cables, provided the system uses the E-Tube communication standard.
Functional Differences in Performance
Performance-wise, both units deliver identical electrical communication speed and reliability. However, the SM-EW90-B offers a broader range of connectivity options, allowing for more complex shifter mapping and customization via the E-Tube Project software.
For example, with an SM-EW90-B, riders can assign different shifting behaviors to each shifter, use synchronized shifting, or add satellite controls without additional hardware changes. The SM-EW90-A, while simpler, limits future expansion due to its two-port configuration.
This makes the SM-EW90-B a better choice for riders who may wish to upgrade their Di2 setup later, while the SM-EW90-A remains ideal for lightweight builds where simplicity and aerodynamics take priority.
Maintenance and Durability
Both models share similar maintenance requirements. They are designed to be weather-resistant and sealed against moisture, but regular inspection is essential. Over time, cable connections can loosen slightly due to vibration and temperature changes, which may cause temporary signal loss.
Mechanics should periodically disconnect and reconnect the E-Tube cables, ensuring clean contact surfaces. Avoid using lubricants or cleaners on the ports—dry connections provide the best electrical performance.
Additionally, verify that the junction box is firmly secured and not under tension from tight cables. On integrated handlebar systems, ensure cables are not pinched or twisted during reinstallation.
Troubleshooting Connectivity Issues
Common issues for both the SM-EW90-A and SM-EW90-B include intermittent shifting, no response from shifters, or lost communication with the system. These are typically related to:
- Loose or damaged E-Tube cables.
- Faulty port connections due to contamination.
- Incorrect cable routing causing tension or interference.
Using Shimano’s E-Tube Project app can help diagnose connectivity issues. The app identifies missing components or unstable connections, simplifying troubleshooting. In most cases, re-seating cables and cleaning ports resolves these issues.
Choosing Between SM-EW90-A and SM-EW90-B
The decision ultimately depends on your bike setup and future plans. The SM-EW90-A is ideal for streamlined builds where only two connections are required, such as TT bikes or minimalist road configurations. Its smaller size and lighter weight suit aerodynamic-focused designs.
The SM-EW90-B, with an extra port, provides enhanced flexibility and is preferred for standard road bikes with dual shifters or planned upgrades. Riders seeking more control or expanded features benefit most from this model.
For professional mechanics, stocking both models ensures compatibility with a wide range of customer setups, particularly when upgrading older Di2 systems or building from scratch.
Summary of Key Differences
| Feature | SM-EW90-A | SM-EW90-B |
|---|---|---|
| Number of Ports | 2 | 3 |
| Ideal Use Case | TT / Triathlon Bikes | Road Bikes |
| Connectivity Options | Limited | Expanded |
| Future Upgrade Potential | Low | High |
| Size and Weight | Slightly Smaller | Slightly Larger |
| Customization Flexibility | Moderate | Extensive |
Conclusion
The SM-EW90-A and SM-EW90-B share the same core purpose but cater to distinct cycling setups. The A model prioritizes simplicity and aerodynamics, while the B model emphasizes flexibility and expandability. Choosing the correct version ensures smoother installation, better cable management, and full compatibility with your Di2 shifting system. Mechanics and riders alike should evaluate current and future needs before selecting the junction box that best supports their electronic drivetrain configuration.