Shimano di2 electronic shifting


Well-Known Member
Jan 15, 2011
I can hardly believe that there's no thread about this so I'll start off:

I was looking for an Ultegra group to put on a bike. I've been Campy for most of my life but after 8 went to 9 and 9 went to 10, keeping the damn things in adjustment so they were shifting properly at least most of the time was getting to be more and more of a pain in the butt.

So I decided to go back to Shimano where brake lever shifters began.

I couldn't find a used Ultegra group and I didn't want to buy a new one only to find that they don't work any better than the Campy with all of those speeds. I finally discovered a guy was selling an Ultegra Di2 11-speed group for a reasonable price and bought it.

Got it home and it was missing the wires, the battery and the battery holder. Obviously the guy owned an internally wired bike. No big deal right? Well, let me inform you. Every piece of a Di2 group has intelligence built into it. That is in the form of integrated circuits. And you have to have an entire group that is based upon, you guessed it - the battery holder. This thing doesn't do anything but hold the damn battery so why do you have to have a special one? And all five or so external battery holders all look alike. Some of them don't even have part numbers on them except in one of those microscopic visual code squares. I managed to buy two of them because I bought one and forgot I had done so and bought another. That's right neither one of them would work. With a good battery and an entire set of matching parts, it was completely dead. Not so much as a hint that it was working.

Now remember that there are several different TYPES of Di2 and there are a whole lot of interchangeable parts from 105 all the way up to DuraAce so that you can upgrade as you go along as long as you stay within the series. Finally the Owner of Stone's Cyclery in Alameda, CA, printed me out an interchangeability chart for my series. The one part that couldn't be interchanged was the battery holder. So I tracked one down in Japan and got it via Ebay (though I should probably have looked on Amazon first). I attached the parts to the battery holder and plugged in the battery and everything fired off perfectly and worked almost perfectly from the start.

Being an electronics engineer by trade I'm rather puzzled why they would use a battery holder as anything other than a battery holder but be that as it may, it worked fine.

The bike I was putting this one is a Redline Cyclocross bike and has hydraulic disks. Well, that year of Ultegra didn't have hydraulic disks so the original owner had bought R785 levers instead of Ultegra. I was a little concerned about bleeding the hydraulic lines but all you have to do is watch one of Shimano's videos and it is an easy process. Worked the first time. They have this so carefully worked out that when you put the little plug in the drain fluid funnel and unscrew it the volume of the liquid in the part below the plug and the amount of volume that you are unscrewing out of the bleed orifice are the same - they don't even drip excess fluid! One of the levers didn't have sufficient pull since the guy that had them was shorter than me. But just below the bleed port on the levers is a lever-throw adjustment.

There are two kinds of rear derailleurs - the SS and the GS. That's the short arm or the medium arm. The GS which I have shifts up to a 34 if I understood them properly. I have an 11-32 on it. The SS only goes up to a 28 tooth. The shorter arm with the smaller cassette shifts a bit faster. Though you couldn't convince me of that since you can hear it change but it is hard to actually watch the motion. It is in one gear and then it is in the next.

It isn't on the road as of yet. I still have some details to work out like cleaning up the wiring runs externally.

But I was impressed enough to start outfitting my 2018 Trek Emonda with the same thing only with direct mount rim brakes. I could find a million things wrong with electronic shifting before I actually tried one. Now I know that I can put the bike on the shelf for 3 months, pull it off and expect it to shift perfectly. My Campy gear will not go more than a month without fiddling with the adjustments and in my dusty garage the multispeed Shimano stuff can gum up with dust from the dryer.

I am not so much of a fan of hydraulic brakes. I think that is an answer for a problem that doesn't exist for the average rider. If you have a set of $2,000 carbon fiber deep aero rims you don't want to rub brake pads on those rims. So disks make some sense. They greatly extend the life of the wheelset. But don't think you're getting away scot free. During the time you're using the wheels the pounding they take will finally delaminate the wheels so it isn't as if it is a lifetime buy. If you're a victim of living in the Pacific Northwest, disks brake better in the wet.

For the rest of us the sheer power of disks is a danger. If you're riding a Cross bike off road there's always a chance that you'll be holding onto the brake levers and hit a hard bump that can cause you to jam the brake on hard and throw you over the bars as I did using a flat-bar group on a very steep downhill. I thought I was falling forever before I hit. Then I was surprised that I was unharmed until the bike landed on top of me..... Some poor kid riding by uphill on an MTB saw it and said, "Uh, are you OK?" "AM I OK???" echoed off the entire countryside hills for half a minute. So the Trek runs direct mount rim brakes.

For those of you that have experience with the Di2 perhaps you'd like to comment on things like external wiring and batteries like you have to use on all of the older bikes. You see this a great deal on Titanium bikes though new ones can get internal wirings pathways.

If you can internally wire a bike how does the bar-end controller work? I can completely recharge my external battery in about an hour and a half from completely dead. It lasts about a couple of weeks and if you haven't checked and it starts getting low the newest software that can be uploaded to any of them kicks the bike into the small ring and then you can only shift the rear derailleur which uses the least power. So you can probably get home. If you run completely dead it will stay in whatever gear it was in. Di2 never turns off. The Stem Unit has some lights on it that you can query for battery condition before or after any ride.

Does the internal wiring which uses a different kind of battery and recharges through a small special connector on the Stem Unit (or bar-end controller) charge as rapidly?

If you're a bike mechanic no need to be too nervous about working on Di2. The most complicated thing after a little break-in time is figuring out the wire lengths. You don't want to get that wrong because they're expensive. Though with internally wired groups there quite a bit of variation you can get away with. With externally wired groups the wires have to be pretty close to the correct length. You also have to use your computer to gain entrance to Shimano's Di2 sites to show you which part is interchangeable with which other part.

SRAM electronic is all radio linked so there is no wiring but also that means that all of the components have to have their own batteries. Some are rechargeable and some have to be replaced.

Campy has an ETS system but I have even seen any of those.

So electronic shifting isn't a fad. And it has a lot of advantages though it comes with its own disadvantages. Damnit, nothing is perfect on a bicycle after all. My Trek will come in almost a lb over the UCI minimum.


Well-Known Member
Aug 13, 2013
I thought you had been banned from this forum for life for posting nonsense and constantly fighting with people.

I guess it's time to bring back the following PSA:

For anyone reading the above post from "cyclintom" , do not take his word for anything, as he frequently posts inaccurate or misleading information that could be potentially dangerous. Make sure that you double-check everything using reliable sources of information before making any decisions that could result in physical or financial harm to you or anyone else. We don't think he does this maliciously, he simply doesn't know what he's talking about and refuses to listen to anyone who attempts to correct him, so don't waste your time. Much of this seems to be due to his suffering a serious head injury some time ago. Unfortunately, he seems to be a lost cause.