Everything You Need to Know About Shimano Di2

Over the past dozen or so years, electronic derailleurs – and in particular the Shimano Di2 in its Dura-Ace and Ultegra versions – have gradually become essential from a certain level of the range up. Ease of use, comfort, precision and speed are the well-known advantages of Di2 systems. But are you sure you know all the possibilities this type of electronic drivetrain offers?

Photos: ProCycleShot/Wouter Roosenboom – Pauline Ballet – Flickr.com – commons.wikimedia.org/DR

Electronic derailleurs are found on many bikes from the mid-range up;

Among the advantages of Di2, comfort of use is often highlighted: you just press a button on the shift lever to change sprocket or chainring, whereas with a mechanical derailleur you have to work a lever until it reaches the indexing point that lets the derailleur settle in front of the right sprocket, often with a larger movement. Di2 does not make you go any faster, but it makes shifting easier, especially in the cold or when general fatigue sets in at the end of a long ride.

A simple press of a button changes gear.

The other main advantage concerns precision that lasts over time. Once the derailleurs are properly adjusted, they cannot move, except in the event of an impact (if the rear derailleur hanger gets bent, for example). With a mechanical drivetrain, by contrast, a cable can rust, go slack or slide less smoothly inside its housing. Adjusting derailleurs is relatively simple to do while riding, for instance after a wheel change during a race, whereas with a cable system you usually have to adjust the indexing directly on the rear derailleur.

Di2 is operated with the button on the junction box, which sits under the stem, at the end of the handlebar, on the frame or in the seatpost depending on the bike brand. A long press gives access to the derailleur settings so you can fine-tune the indexing with small taps on the levers. This button also lets you change the shifting mode, which we will come back to later.

The junction box has been discreetly placed on bikes since the Di2 generation that appeared in 2017.

The system also automatically aligns the front derailleur position based on the rear sprocket chosen, to avoid rubbing. Let’s add that Di2 makes it easier to route the electrical wires through the cockpit or frame than a cable drivetrain does, for a cleaner look and better aerodynamics.

=> SEE ALSO: Riding faster by being more aerodynamic

That covers the main innovations users appreciate in these systems, but there are still plenty more to discover.

Options that are often overlooked

Many Di2 users use it the same way as a cable drivetrain. That is a shame, because the electronic drivetrain offers customization options for the cockpit or the shifting mode that are often overlooked, and they deserve a closer look.

An extra shifter on the bottom of the handlebar is popular with sprinters.

With Di2, you can fit satellite shifters in places other than the brake/shift levers. So an extra button can be installed on the lower part of the handlebar, called the “sprinter shifter” by Shimano, which lets you change sprocket with a flick of the thumb with your hands on the drops. Another button can also be installed on the top of the handlebar, called the “climber shifter”, to change gear while keeping your hands on top. These same satellite shifters can of course be placed on triathletes’ aero extensions or on time trial bikes, which always gives you a double set of controls in two different places on the cockpit. Connecting the various shifters is made easier by a simple electrical wire, much easier to route inside the handlebar or under the bar tape than a steel cable.

Triathletes also benefit from extra shifters, which can be placed at various points on the cockpit.

But that is not all. Mechanically, an electronic shifter for derailleurs is much less complex than a cable shifter. The Di2 shifter has three buttons (with a third button hidden under the rubber cover), linked to an electronic unit. This means you can make these buttons do whatever you like: use them as standard shifts, with the right lever controlling the rear derailleur and the left lever the front, or swap everything around. This is useful for people with a disability, for example, or for following particular preferences. The extra button under the cover can be used to shift gears, or to control the menu pages of a compatible computer, provided you install a small Bluetooth sensor in the system. This last option lets you see information about the drivetrain displayed directly on the computer, such as battery level or the gear you are in.

The brake cover hides a third button that you can activate if needed.

Several different functions can be assigned to this button.

It is also possible to customize the action of each button, either by adjusting how quickly the gears change on each press, or the number of sprockets shifted after a long press. For example, you can choose to sweep across the whole cassette while keeping your finger pressed on the lever, or only one, two or three sprockets, to avoid mis-shifts.

Sequential shifting

In our view, the main interest of this customization lies in the choice of shifting modes. Because Di2 (in both Dura-Ace and Ultegra) offers synchronized or semi-synchronized shifting options. This means you can use the drivetrain as a sequential gearbox. There are three modes, which you can select with a double click on the junction box button:

“Synchronized” mode: with each press of the rear derailleur lever, the system directly shifts to the next lower or higher gear and automatically activates the front derailleur to follow the gear range. You can choose through the app which sprocket of the cassette the shift to the other chainring happens on, and you can always shift the chainring manually.
“Semi-synchronized” mode: when you go from the small to the big chainring or the other way round, the rear derailleur automatically compensates for the difference in gear ratio by changing the rear sprocket itself, so as to keep your pedaling cadence steady. Depending on the cassette’s tooth spacing, the rider chooses how many sprockets are shifted with each operation.
“Classic” mode, using the electronic derailleurs like cable derailleurs.

The Di2 drivetrain can be used as a sequential gearbox, using only a single lever.

Easy-to-access software and app

All these settings and customizations are made from PC software (E-tube Project), with a cable to connect to the Di2 system. It shows the status of the various components (to detect any malfunctions), keeps the firmware of the electronic parts up to date, and therefore offers the ability to configure the controls. This free software is the same one used to communicate with the Shimano power meter, or with the Shimano Steps e-bike systems.

E-tube Project lets you customize how the derailleurs work.

To set up the shifting modes, you enter the tooth counts of the chainrings and the cassette, and the system shows the gear ratio of each available combination. You can then choose when, and on which gear, the automatic chainring shift happens if you select synchronized mode.

With a pair of 53 and 39 tooth chainrings and an 11-28 tooth cassette, for example, you can decide that with each press to go to a smaller gear, the chain climbs to 53/25, then automatically switches to 39/21 (the next lower gear). You can of course also choose to go only as far as 53/23 before switching to 39/19, depending on your preferences. In the other direction, you can decide that the chain stays on the small chainring up to the 15-tooth sprocket, before automatically switching to 53/19 on the next press of the button. And all of this happens with the utmost smoothness, thanks to the power of the derailleurs and the shape of the chainrings, which makes for extremely precise shifts.

E-tube Project is also available as an app for smartphones or tablets, which is very handy for those without a PC. In this case, the system communicates via Bluetooth through the small optional sensor (the D-Fly) that we mentioned earlier for the connection to the computer. The various drivetrain settings are just as easy to use as in the PC version.

The real weight of Di2

A few rare detractors of the Di2 system point to a supposedly higher weight compared with cable drivetrains. What is the real story? When comparing the weight of several groupsets, you have to take into account all the parts needed for them to work, which of course includes the weight of the cables and housings needed for mechanical derailleurs, which are replaced by light electrical wires on Di2. That weight often offsets the presence of one or more batteries on an electronic groupset. Electric derailleurs with a mini motor are also heavier than mechanical derailleurs, but on the other hand the brake/shift levers are lighter (with electronic components instead of a mechanism).

Di2 groupsets are very slightly lighter than mechanical groupsets, contrary to popular belief.

On the scale, the Shimano Dura-Ace Di2 11-speed (rim brakes) turns out to be 20 g lighter than the mechanical version. For the disc version, the weight is equivalent, within 5 g. At Ultegra level, the difference even reaches about sixty grams, again in favor of Di2, whether with rim or disc brakes.

Proven reliability

Finally, the question of the reliability of such a system often comes up, and rightly so if you consider the extra investment needed to switch to Di2. Among the pros, no rider today uses cable derailleurs, although a few reluctant champions, such as Fabian Cancellara in the early days of Di2 or Peter Sagan in some editions of Paris-Roubaix, left some doubt on the matter. Today, riders use electronic derailleurs whatever the terrain or conditions, which tends to demonstrate the reliability of the Di2 system. The argument can be seen as debatable when you consider the resources of some professional teams, for whom replacing a derailleur or a battery is not really a financial issue. However, we can only note the massive use of this technology today in cyclo-cross, gravel and even mountain biking, with riders equipped by Shimano, in the most extreme conditions: rain, mud, dust, impacts, frequent high-pressure hosing…

Operating problems most often come from a flat battery or a disconnected wire. The system is overall very reliable, as shown by its use in off-road riding.

If there are failures, they most often come from the battery when it has not been recharged. This has no long-term consequences. Obviously, you need to remember to recharge the main battery regularly, but it still offers a range of 2,000 to 4,000 km depending on conditions of use. That is enough to go by without stress. Finally, one of the rare battery-related issues that can occur with Di2 comes from storing the bike: a button that stays pressed for several long minutes, for instance when the bike is leaning against another object, drains the battery. Worth checking when transporting the bike.

A step toward the future

Unlike disc brakes or tubeless tyres, for example, the Di2 drivetrain does not divide users or potential buyers, most of whom agree on its ease of use, precision, reliability and ease of maintenance.

Only the higher price of this type of drivetrain compared with standard derailleurs can hold back the most hesitant, but these prices go hand in hand with the overall move up-market of all bikes on the market. Moreover, with this technology available on the Ultegra groupset, slightly less luxurious than Dura-Ace and not much heavier, you get just as precise, durable and complete operation, with exactly the same features, at more affordable prices.

With Di2 and hydraulic braking, modern bikes benefit from a neat integration and a clean cockpit.

Finally, the various features that are well established but that some may still be discovering point to other innovations in the future, with other possibilities, and why not fully automatic gear changes, with derailleurs connected to a cadence or power sensor.

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