105 R7100 Di2

What is Shimano’s Di2 in detail, first successful electronic shifting system


Electronic shifting is not a Shimano invention, but it’s Shimano who did it commercially viable. It all started with Shimano Dura Ace 7970 Di2 in 2009, for road bikes, then came

shimano 105 di2 RD R7150
Shimano 105 di2 RD R7150 rear derailleur. Just a few years ago, I’d wonder if my road bike rear derailleur could properly work with a 11-32 cassette. Today, this 105 rear derailleur happily accepts 11-36 cassettes!

the XTR version for MTB, GRX for gravel bikes, and Alfine Di2 for gear hubs. First Di2, Dura Ace 7970 Di2 and newer Di2 versions are totally incompatible: the 5 plug version is very simplistic: it’s just wires connected to switches and derailleurs across junction boxes. Newer Di2 versions though, use CAN bus for communication between components. CAN bus is known for its extensive use in all modern cars, and became the norm for even the cheapest ones in late 2000’s. But CAN bus, being a data communication protocol, can be used in anything, and it is, including machinery.

Unlike Sram’s eTap, which is designed to be wireless from the ground up, Shimano isn’t a wireless system. The latest iterations are “somewhat” wireless, albeit the fact that rear derailleur is the “master” unit that receives the signal, and still distribute the signal with wire, to front derailleur. This makes Di2 system harder to install to any bike: especially to road bikes. Very latest versions with wireless shifters does not need wires for shifters and junctions boxes, which makes the system much more reliable, easy to install and more streamlined.

Di2 means “Digitally Integrated Intelligence”. That’s a such a bold claim, right? A bit of an exaggeration?  Yeah, I can see some sort of digital integration involved, but intelligence? It sounds like a miniature DC motor operated derailleurs with push buttons on shifters to me, then with some software-induced fanciness. But intelligence? C’mon!

What is Di2, in simplest form

Di2 is a electronic groupset, or at least part of it, with DC motor driven front and rear derailleurs, and special shifters which are no more than glorified electrical switches. Di2 is meant to be used for road bikes, but after quite a long period, some XT and XTR MTB groupsets were introduced,

ST R7170 R
ST R7170 – Shimano’s 105 Di2 shifters are now wireless and accepts 2 CR1632 batteries. I wonder how long will that silicone gasket last, but under 40 c sun, with sweaty hands, I’d want to depend on it. Probably we won’t see a working shifter after a decade on eBay, while much older 1050’s will go crazy expensive and still going strong.

too. Then comes the Alfine Di2, which is a rear gear hub. For MTB, you can buy Di2 for 1x systems, but this somewhat makes an electronic groupset pretty meaningless, as Di2 is still much more expensive, not repairable, not any lighter then already great working mechanical brothers.

Inheritently though, a “theoretical” electronic groupset would be much more reliable, robust, precise and even cheaper: shifters are nothing more then simple electrical switches, cables are just cables which are more simpler compared to piece of art Bowden cables we use today, and most derailleurs use toy motors, which are not more then a few dollars. It’s tiny plastic gears that makes such systems fail, and they are not replaceable.

Use of electronics permits adding some level of fanciness to whole system, like bike GPS connectivity that I’m gonna talk about a bit.

Sram makes eTap, Campagnolo is in the game with EPS, and FSA is the latest contender with K-Force WE. Looks like WheelTop, a Chinese manufacturer tried its luck with something looks like a Sram “replica”, but disappeared later.

Di2 does not special cassettes, cranksets, chains to operate. You may leave your mechanical DuraAce (provided they are both same speed, front and back) intact, and move to Di2 with just replacing shifters and derailleurs, and buy a battery. Also some accessories like cables, junction boxes, even grommets are needed, and these are not anywhere near “cheap”.

Di2 is not only for shifting: D-FLY and E-TUBE

We cannot do anything without connecting to some device, mostly smartphone, these days. Biking is included: you have to document your progress and analyse your performance, as if the world cares.

Shimano has a fancy word for good old Bluetooth / ANT and ANT+ connectivity and it’s D-FLY. Basically, Shimano and electronic equipment manufacturers for

junction box SM EW90 A
Junction box SM EW90 A. Biggest news about latest Di2 groupsets is not wireless, not how many speeds they have, how fast it is. The best news is, confusing, fiddly, expensive junction boxes are now gone.

bicycling, be it GPS or powermeter crank, partnered to mutually support their equipment.

If I was a pro-biker I’d definitely go for it, if my team / sponsors wouldn’t give it to me for free. Otherwise I’m pretty happy with my current setup, which is a 25$ bike GPS, a Strava account and mechanical groupsets. However, for any electronic groupset, such wireless connection protocols is almost a necessity, as adjusting these groupsets otherwise would be very finicky – in Shimano Di2’s case this is E-Tube. I have zero interest in its specifics. I’ve been coding for more than 35 years, created some wireless stuff for fun using microcontrollers, yes, Bluetooth included. I designed maps for fuel injection systems. I hacked fuel injection systems. Bottom line? I’m not interested in such stuff. My life is already loaded up with “technology”, and bicycles is a mean of escaping from it for me.  Yet I’m attracted to all new technological stuff as I’m a curios person, that doesn’t mean I’ll keep them in my “sacred chamber”. I’m not the type of person that “finds” a conspiracy or a deeper plot in every new thing. I love progress. Just not ready enough to shell out 5.000$ for a wireless groupset. For me, it just doesn’t worth it. Extra $100-150 and with a “repairable”, more open design, I’m all in.

Di2 Hardware – What is a junction box ?

Junction box is the most confusing part of any Di2 groupset. Unlike Sram eTap that runs completely wireless, Shimano’s Di2 uses cables. Sram is far superior in this sense: they intelligently placed distinct batteries for each derailleur, then use wireless communication, which completely dismissed the need to use a “junction box”. Another great advantage of Sram is, since there are no cables, boxes and batteries to tuck in & run thru, it can be installed on any bike.

Shimano Di2 system needed special frames from day number 1, because they obliged to run the cables inside the frame. Shifter cables run into seat tube, where the battery is placed, inside seat post. Then, there should be an exit nearby front derailleur, so signal and energy can be fed to it. Then another set of cables from battery runs to rear triangle end, so it can connect to rear derailleur in same fashion. You also need to have compatible stem to mount the junction box.

Later models are less intimidating in this sense as Shimano went semi wireless, which is still not ideal. In first Dura Ace 7970 model, junction box is a simple box where you plug the connectors – or at least, it looks like so. I’m not interested in 7970, as it already phased out afterwards, and later models use CANbus communation. Ultegra Di2 6770 and up, Shimanı came up something called E-tube: think it like an “intelligent” box with PC / Smartphone connectivity; this new generation junction boxes also enabled firmware updates, and adjustment on PC / Smartphones.

Shimano likes to boast about Di2 a lot, and generally have excellent pages about their groupsets, but there is almost no info to use which junction box or cables with which unit. That’s the greatest culprit with Di2 systems. If I were to buy one, I had to research for days, which component is necessary, and will it ever fit my bike. Finally, I figured it out, but not from Shimano based info: I crawled among lots of bike parts sites, and get to know it.

shimano ultegra di2 front derailleur fd r8150
Shimano Ultegra Di2 Front Derailleur FD-R8150. Not the most elegant front derailleur made by Shimano, but kudos for them making it smaller then the saddle this time. Front dereailleurs in electronic shifting requires more horsepower to shift compared to rear derailleurs, and this one looks much neater than previous generations.

Which junction boxes do I need ?

A horrible thing about Di2 – you don’t know what do you need, and why. Well, I’ll try to simplify it for you.

First of all, think Di2 as 3 generations: if you have the first DuraAce, game over for you – you have to stick with it. Then you have the others until wireless shifters. Di2 setup differs for wired and wireless shifters.

Things will get quite complex, so bear with me. I’ ve been thinking about hours how to simplify this, so I’ll come up with simplest explanation possible!

Shimano currently offers 6 modules for connecting your derailleurs and shifters. 4 of these modules are intended for wired models, but also shared amongst both wired & wireless, and the other 2 is explicitly for wireless connection, or communication.

Before getting into details, I’ll simplify it further:

First, you have to know what Junction A and Junction B is: Junction A connects wired shifters to Junction B. Simple as that. Normally, you’ll probably only use 2 STI shifters. But if you want more, Shimano also offers satellite shifters. You can all connect them to Junction A, which resides under stem – which has to be Di2 compatible, obviously!

Then there is Junction B, which is mandatory on all systems, except the latest wireless models like DuraAce 9270 shifters, where the rear derailleur doubles as the wireless receiver. This connects battery, front and rear derailleurs and Junction A, if exists (when you’ re using the wired setup)

Consider yourself lucky, as most people rightfully give up at this stage.

How many ports do Junction boxes have ?

All Shimano junction boxes start with “SM” designation -first, let’s have a look at Junction A boxes. Currently, they have 2 models: SM-EW90-A, which has 3 ports, and SM-EW90-B, which has 5. The difference is, you can connect 2 additional shifters to SM-EW90-B, like ST-R9160, ST-R9180, or ST-R8060 bar-end shifters, or satellite shifters like SW-R9160. Simple to grasp: one port is dedicated to cable running to Junction B; 2 for shifters, left and right on SM-EW90-A. If you haveSM-EW90-B, again, one port is for Junction B connection, and 4 for shifters: 2 for STI (brifters) and 2 for satellites. Easy, right?

If you have wireless shifters like Dura Ace ST-R9270, Ultegra ST-R8170 or the new 105 ST-R7170, you don’t need Junction A box!

Shimano EW-RS910 ?

A trimmed down Junction A box, meant for previous generation Dura Ace, just before the wireless shifters came. It tucks nicely into the end of the sidebar, if compatible, as this Di2 obviously! Probably most previous DuraAce Di2 owners are quite pissed off after the (semi) wireless new DuraAce, which left them with lots of cables and plastic boxes to hide.

Which Junction B box do I need ?

Ok, here comes the last hard choice. Once this is settled, it’s quite easy to move on with Di2 🙂

shimano bt dn110 a di2 battery
Shimano BT-DN110- a Di2 battery. Replaced by DN300, which has 3 ports. With 3 ports and wireless shifters, junction boxes eliminated for good. But sticking a battery into your seatpost may not be the most elegant solution.

These boxes start with “SM” designation as Junction A boxes, but luckily it’s much more straightforward: there are 2 models, one bolted under the bottom bracket ( SM-JC40 ) and the other resides in the bike frame ( SM-JC41 ).

I think SM-JC40 is bit of an afterthought. I personally wouldn’t put a plastic box under my 5.000$ carbon fiber frame, and band-aid some cables after paying 3500-4000$ for DuraAce Di2. I’d rather go for Sram eTap, which I didn’t like for their weird shifters on mechanical groupsets, but with electronics, no problems for me at all!

Di2 Hardware – Which battery to choose for my Di2 setup – batteries not included

Shimano is more consistent with batteries, and looks like there is only two available now, BT-DN300, and BT-DN110-A– capacity-wise, they are the same and the only difference I spotted is, the former have 3 e-tube ports instead of 1. This is because ST-R9270 and ST-R8170 shifters does not need a Junction B box: they can connect directly to BT-DN300 battery unit, IF you opt for the wired option, as they are also wireless. You might ask: “But then, battery has to have 4 plugs, 2 for shifters and 2 for derailleurs, right?” – Not necessarily: because ST-R9270 and ST-R8170 shifters have 2 E-TUBE ports: For example, you run a cable from left shifter to right shifter, then one cable to battery on the remaining plug on right shifter. What about satellite shifters? They are covered, too: each shifter have additional one port for satellite shifters, which is not E-TUBE compatible. One thing to note here is that, ST-R7170 shifter, which is the new 105 Di2, is purely for wireless use, meaning you can’t connect them with wire, and also cannot use satellite shifters with them.

So this makes BT-DN300 practically compatible with anything released with Dura Ace 9270 shifters and up.

As BT-DN110, having the exact same form, BT-DN300 houses inside a Di2 compatible seatpost.

Unlike any manufacturer making a device with Lithium Ion battery, claiming they are “great” for 500+ charge cycles and good for 1000, Shimano tells the truth: battery units are good for 300 charges. Indeed so. Luckily, it uses 2 ICR14430 batteries internally and I’m pretty sure it is user serviceable. Not to mention user manual will say no serviceable parts inside, and attempting repairs will cause a second Fukushima disaster, if not in larger scale. I newer get my hands on this one, as I’m too poor to afford a Di2 groupset.

How older models have Bluetooth / ANT+ connectivity, without the wireless derailleur ?

Anything under latest wireless models do not have Bluetooth / ANT+ connectivity inbuilt – this is now handled in rear derailleurs. Older models need to rely on either EW-WU111 or EW-WU101.

Both EW-WU111 and EW-WU101 does the same job; provide Bluetooth and ANT+ connectivity. This is used by Shimano D-FLY compatible devices, or Shimano software. More on that later. The only difference between them is, EW-WU111 is inline with a port on each end, while EW-WU101 have 2 plugs side by side on one end – why? EW-WU101 is meant to be used outside, nearby seatpost or right rear lower arm, where EW-WU111 is an inline model, hidden inside the frame, best to be placed near stem because obviously, frame will act as a Faraday cage and reception will be lower compared the  EW-WU101.

Both models replaced the historic and long-time obsolete SM-EWW01 model, which is not compatible with anything Di2-related now: neither plugs or software will work with it.

Di2 cables

A high end product should come with excessively expensive cables with proprietary plugs, and incompatibility amongst the generations is the icing on the cake. Both the current EW-SD300 and previosu generation and now obsolete EW-SD50 cables ticks all the boxes. They have many sizes to choose from, 15 cm to all the way up to 1.6m. They are about 30$ each, and you need (unless you go latest-gen, wireless) 6 of them. As far as I can remember, Shimano makes some groupsets cheaper then 6 cables combined. Luckily, latest gen is fiber optic but uses tachyons instead of ordinary photons, which have the ability to go back in time, so you can rollback your latest mis-shift in alternate reality. I’m kidding. Partly. Tachyons can do that. But cables can’t, and they’re copper, or aluminium, who knows which…

Di2 for MTB

display unit SC M9051
Display Unit SC M9051. A neat unit indeed, but instead of shelling out 200$ for it, I’d probably buy D-FLY compatible GPS bike computer instead, which does what this does, plus doubles as a full fledged bike GPS.

Di2 is meant for road bikes from the beginning, and that was the correct path to go: MTB derailleurs work in more challenging conditions, which is not a good idea to test the new paradigm. 1x movement didn’t help too, yet Sram released a 1x MTB electronic shifting, which don’t make sense to me: the real advantage of electronic shifting is changing all gears up and down with just 2 buttons, without thinking about cross-chaining or matching front and rear gears for getting gear ratios right, which Shimano calls “Syncro shift”.

Most ancillary items like batteries, cables, or junction boxes shared across road and MTB lines.

Recent bad news for MTB riders who are aiming to go electronic: Shimano killed XT Di2 for MTB, and make it available for “E-MTB” only. Hmm. I think Shimano have never been clear enough with the perfect XT line: some years, they released XT for MTB. Then, XT for trekking. Some years, both. XT have been always the best choice if you have some cash to spend over Deore, Di2 included: it was way cheaper then the XTR line which do not have much to offer to justify the huge extra cost. Well, you know why XT is no more for MTB by now…This is a clear consolidation of XT and XTR into XTR line, which is obviously top of the line, but frighteningly expensive.

That’s a pity. Shimano, instead of killing Ultegra, added 105 to the Di2 line for road bikers. I believe we can expect Deore Di2 anytime soon.

Surprisingly, XTR is still fully wired, yet it’s much easier to setup a Di2 system on MTB. They have fewer components because there is less concerns about being “somewhat backwards compatible”, as MTB line released much later than Di2 for road bikes.

XTR M9000 series, which is the latest iteration of Di2 for MTB’s, is 11s. One good thing for tourers is, you can also have 2 or 3 chainring choices. I was worried that Shimano would 3 chainring for good, but luckily that didn’t happen, at least for now. Having stuck at “just” 11s may seem a bit old fashion these days, but I think Shimano designed this groupset for tourers, casual riders, or trail riders in mind instead of racers (which contradicts the XTR image altogether).

Shimano Di2 Gear Hub: Alfine Di2

Shimano makes two lines of gearhubs, Nexus and Alfine. Nexus is the cheaper line up, which is 3, 7 or 8 speed; while “premium” line Alfine is 8 or 11 speeds. Not still on par with Rohloff, which is 14 speed and have an electronic version, but it’s much cheaper, and you don’t have to send the unit to Germany for full overhaul. It’s much like driving a Black-line E class Mercedes AMG car or Koenigsegg Gemera: obviously, Gemera is much more advanced in any way, but you’ re stuck if it breaks. With a

alfine display SC S705
Alfine display unit SC S705 is pretty ugly stuff. I’d probably skip this one, if someday, for unknown reason, I decide to buy a Di2 Alfine, instead of perfectly fine mechanical one.

Mercedes though, you’ re covered in even the most remote places on earth. I’d prefer the former as a daily drive, as most people would prefer the cheaper, abundant and serviceable Alfine Di2.

Frankly, I see no point in having an Alfine Di2: you only have one shifter to operate, and unlike rear derailleurs with Bowden cables, it won’t misshift as often, and people mostly prefer them for their simplicity. Why add a few things that can break and make a unit inoperable, probably otherwise serve a few generations? You know what? I’d prefer the “mechanical” Alfine to Alfine Di2, if it’s even a bit pricier. I can see it’s a selling point for a bunch of rich customers. But anyone riding bikes with gearhubs previously wouldn’t like the idea of putting a battery into seat post, carrying a charger, adding an extra complexity to already hard to maintain, but rock solid gear hubs. They’ re already perfect for the task, which is mostly simplicity and trouble-free operation for decades, so why ruin it?


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