Review: Shimano Dura-Ace Di2 9150
Aug 31, 2020
article & images by Nick Salazar
We're going to look at every aspect of this group, but we will start in an odd place: the wires. One of the first questions I get about Di2 builds is "what different lengths of e-tube wires do I need?" This is a bit of a tricky question. Or rather, it's a very straightforward question, but difficult to answer in a universal way. That's because Di2 can be configured in a lot of different ways. Different shifter configurations, different A-junctions that can be used in different places, different batteries and battery locations, etc.
So really, the first question you need to ask is "where am I putting everything?" Some things are easy to locate; the derailleurs have only one spot to go, and for triathletes, shifter locations are also fixed in place at the extensions and brake levers. So the first question we face is where to put the front junction, also called the A junction. This is the part that provides the system's main adjustment button and the charging port, and you have to have one in every Di2 installation. For this build, we used the newer EW-RS910 junction, which fits nicely into the back of an aero extension. And our battery is the internal version, the BT-DN110. Yeah, Shimano's part names are not exactly memorable, but there is at least some consistency. EW abbreviates something like "E-Tube Wiring" and BT is probably short for "battery." Other parts like the BL-TT79 are the Brake Levers, for a TT bike. So it makes some sense, even if it's easy to get confused.
The rear junction, also called the B-junction, or the "secret black box," is merely a wire connector. It takes all your e-tube wires and connects all the positive and negative strands together. So there's no limit on how many you can use, or where you can put them. They are essentially just splicing wires together. For this build, we had two of them up front (to sort out all the connections between the shifters, brake levers, and A-junction). Then we have one more in back to sort out connections to the derailleurs and battery.
Finally, the battery. We are using Shimano's internal battery, which I like to call the "lipstick" battery. It has had different names through different generations of Shimano drivetrains, but the form and function remain the same. It's small enough to fit inside most bikes, and some seatposts. The seatpost on our Omni is too narrow to fit the battery, so we put it inside the frame itself. I like to wrap it in a little protective material (foam, bubble wrap, or even just a nitrile glove) and gently nest it in place. It never needs to come out, at least not for many years, so it's safe to put in place in a semi-permanent manner.
Ok, that's all the components sorted, so we can finally address the original question: which wires do we need?
Once we know where all those parts go, it's a trivial matter to figure out what wires we need, and how many of the SM-JC41 rear junctions we need. I have no idea where that part name comes from … maybe "small junction, four wires, one signal" or something like that? Anyway, in our case we need three of them. Two are needed to handle all the front-end wires, and there's one in the rear to handle the derailleurs and the battery. Then we need the E-Tube wires themselves. I almost ALWAYS get wires that are a little longer than necessary. It's relatively easy to stuff 100mm of extra wiring into a space, but almost impossible to use a wire that's 10mm too short.
Starting from the front junction, I use a 400mm wire to go up to the shifter that's on that same extension, then a 200mm wire to go from the A junction to the first of the two JC41's inside our Alpha One base bar. To keep things simple, that JC41 connects to the other extension shifter, and then chains to the second JC41. That second JC41 is packed: its first wire is the daisy chain connection, two more connect the two brake lever shifters (they have their own integrated wires, no need to pick a length), and its fourth port goes to the back of the bike via a 1200mm E-Tube wire to the final JC41 in the back. I use 1200mm for that main wire, and I'm on a size Medium bike. The wires go as long as 1600mm, which no one really needs, but it's available. The 1200mm is already overkill on this size Medium (about 1000mm would do), but again I like to be on the safe side, and it's so easy to tuck in the excess wire, especially on a frame with as much internal space as Omni.
In back, we have three more wires. I used a 600mm wire for each of the two derailleurs, and another 600mm for the battery. Again, all longer than needed, but very easy to tuck in. And the total excess weight I've added to the entire bike is likely less than 50g.
I didn't end up using the EW-WU111 module, which simply daisy-chains in anywhere in the system (one wire in, one wire out) and adds Bluetooth functionality to the system. It's an $85 part that you can add at any time, and lets you customize the bike's functions via computer or app, without using the much more expensive (and possibly deprecated?) SM-PCE1 module. I was happy with all the default functions and settings, so I left it out, but it may be an option for the future.
Ok, our parts are installed, and we're wired up, on the next page let's talk about the components themselves.