Let’s face it… Shimano’s traditional understem Di2 junction box is unsightly. Yes, it’s functional and allows for more connections if you need them, but it isn’t pretty. Thankfully though, there are better ways to keep your Di2 system rolling. Some frames feature an integrated Di2 location, which is super-slick. But, for frames without that feature, did you know you can use that same Shimano EW-RS910 unit with a compatible drop bar? I did just that as I updated my cockpit, and I’ll show you the results.
Shimano EW-RS910 Di2 Bar End Junction Box Features:
- Frame mount or bar-end mount options
- 2x E-Tube ports
- Integrated charging port
- Single function button with LED indicators
- Includes two bar-end install sleeves
- Compatible with all current Di2 systems
- MSRP: $116.99
Simplifying my Di2 cockpit
The under-stem Di2 junction box (SM-EW90 A/B) is the most common junction box used with Di2 systems. And, it’s most often mounted underneath the stem. It makes for a convenient location to attach shifters or accessories, and it can accept up to 5 connections. It’s still the standard option for triathlon, but if you are running a standard road or gravel setup, the RS910 bar end junction box does the trick.
Before transitioning to this unit, keep in mind that you will likely need a new Di2-compatible bar. Many new bars are compatible, but we can’t recommend drilling holes in your existing bars (don’t do it). These bars feature holes to route the E-Tube wire by both hoods or under the stem. Most bar ends are also reinforced to accept the junction box. Both the latest versions of the ENVE Compact Road Bar (tested) and the Zipp Service Course SL-70 Ergo include proper holes to mount the Y-Split E-Tube wire (EW-EC130) from the hoods down to the bar end.
Again, you’ll need:
- EW-RS910 unit
- Compatible drop bar
- Y-Split E-Tube Rooting cable
- Additional E-Tube cables of various lengths
- Electrical tape
- E-Tube connecting tool
As I started planning this out, I was able to carefully measure the distances and get cables to match. Even though there are only two ports on the EW-RS910, so long as you’re not using sprint shifters, all you’ll need is the Y-Split to connect the junction box for proper charging and system configuration. The other shifter can be controlled with the extra sprint shifter port from one of the shifters (the right one, in my case). I then ran an E-Tube wire to the left shifter. This can even be done internally, if your bars can accommodate it and if you’ve got the proper tools and patience.
When attaching the bar end mount, each piece has double-stick tape that can be used to secure everything in place. I just used a few wraps of electrical tape instead and it’s just as secure — if not better. It does extend out 6mm from the end of the bar and the protective ring keeps the junction box from being damaged. The attachment wings do add a little bump to the top/bottom of the end of the bars, but the biggest challenge is wrapping. As you can see above, if you don’t do a taper cut at the end of the bar tape, you’ll get a bulge. It’s not the end of the world, but when I re-wrap, I’ll have to try a taper cut to one side of the tape as I begin to wrap the bars.
The end result is a slick bar-end unit that stays out of the way, looks sleek and functions perfectly. I can charge the battery, check status and perform micro-adjustments with ease. Something that I really appreciate is not having the under stem junction box getting in the way every time I grab my bike. I have a tendency to grab my bikes by the stem because it’s always a secure location. However, with a Di2 junction box under there, it always had to be a delicate grab or else I’d disconnect the strap inadvertently. Not only do I love the looks, but I love being able to grab the stem without worry.
- Love the sleek look without the under stem box and rubber strap
- Can grab the stem with confidence
- Improves access to charging port and function button
- Can fully route all cables internally
- You’ll likely need a few more E-Tube wires
- Changeover is still pretty expensive (~$200)
- Bar tape requires some trial-end-error to avoid the bulge
The Bottom Line: Shimano EW-RS910 Junction Box
While this firmly goes in the “nice to have” column if you already have a functioning Di2 setup, it’s really, really slick. If you are building out an Ultegra R8070 or any other Shimano Di2 build, plan on this one. It offers a much sexier aesthetic and allows for a reduction in unsightly E-Tube wires around the cockpit.
Buy Now: Available at CompetitiveCyclist.com
Hi, at the moment I am using a external battery. Can I install a EW-RS-910 with a seatpost battery? The older derailers, will I be able to update software from the charging port? Thanks John.
How old is the Di2 system you’ve got? That’s the way I’ve done updates and charging with a seat post battery, so you should be good.