Di2 Secrets

by | Gear

Switching Gears

I recently had an issue with the front derailleur on my Di2 setup. Electronic gears are great, and rarely need adjusting, but this was a new build and I wanted to micro adjust the front derailleur?position. Apparently, Shimano?doesn’t particularly feel the need to advertise how this is done and it took a few forum searches to find the answer. In the process I found another neat feature, so thought I would share the information.

The little junction box, usually located at the stem, is the key to making these adjustments. Knowing?some simple inputs gives you access to all the features. The junction box has a couple of cable inputs, a little door at the side for connection to the charger, two LED windows and a small and somewhat stiff button on the top.

Here is a quick article explaining how to

  • See how much battery charge you have left
  • Adjust the rear and front derailleurs
  • Change from Manual shifting mode to the new Semi Auto and Fully Auto shifting modes.


Battery Charge

First, the boring stuff. How much battery charge do you have left? Press and hold one of your gear shifters and the battery indicator light will signal the amount of charge left.

  • 100% – Steady green light
  • 50% – Flashes a green light three times
  • 25% – Flashes a red light
  • 0% – Steady red light

When you ‘almost’ run out of juice the front derailleur will stop working, usually in the small chainring. I am not sure 100% whether it is the small but that seems to be the one that everyone ends up in with a flatter battery.

One you are fully out of juice the rear derailleur stops working in whatever gear it was in.

As a side note, there is a little device that you can install that sends info via Bluetooth to a compatible Garmin or smart phone app. This can read the battery status too.


Rear Derailleur Adjustment

Making adjustments to the front derailleur is easy. Simply push and hold the button on the junction box and the shift LED should emit a steady red light. From there simply hit the rear derailleur shifter to micro adjust the rear derailleur. You can do this whilst riding to find the sweet spot. TIP – Remember how many shifts you have made and which direction you shifted, that way you can get back to where you started if required. The micro adjustments will help trim the rear derailleur for smooth shifting and to problem solve chain rub / noise. It shifts in tiny amounts, unlike a normal shift which changes from one cog to another.

Press and hold the junction box button again and the red LED will go out. You are now ‘out’ of adjustment mode.

Click the link for the official Shimano PDF – page 64 for rear derailleur.


Front Derailleur Adjustment

NB: Requires the Generation 2 version of Di2 with the latest firmware upgrade as of June 2017. It may not work on 10 speed versions.

This is where things get interesting. Actually, it is no more complicated that adjusting the rear derailleur but?it was hard to find how to put the front derailleur into adjustment mode to begin with. ?Unlike the rear derailleur, which can be put into adjustment mode simply by holding the junction box button down for a couple of seconds, the front derailleur requires you to be in a specific gearing.

To start, you need to be in the ‘Big Cogs’.

  • Change to your largest gear in the front, the big chainring.
  • Change to your easiest gear in the back, your biggest cassette.
  • Press and hold the junction box button until the red LED stays lit.

Now you can micro adjust your front derailleur.

Click the link for the official Shimano PDF – page 69 for front derailleur.

Adjust Shifting Modes

NB: Requires the Generation 2 version of Di2 with the latest firmware upgrade as of June 2017. It also requires E Tube Components, which most newer models have. It does not work on 10 speed versions.

So, we’ve made the bike work and shift smoothly. Now we can turn our attention to how it shifts. Shimano created a firmware upgrade that allows you to select how the derailleurs act when you change gears. There are basically three modes. I believe they are officially called S1, S2 and S3, with the ‘S’ standing for Syncro Shift I think, but for descriptive purposes let’s call them Manual, Semi-Auto and Automatic.

MANUAL (S1) – This allows you to shift as normal. Rear shifters for the rear derailleur, front shifters to change front derailleur.

SEMI AUTO (S2) – This mode takes care of the rear adjustment when you shift the front derailleur. Usually, when you change your front chainring you also change the rear gears to allow for a smooth gearing change. Move from small to large chainring and you usually drop a couple of gears in the rear to accommodate. Semi Auto (S2) does that rear shifting for you. For example, when you change from small to large chainring, the Di2 automatically chooses a suitable gear ratio on the rear cassette.

AUTO (S3) – This mode removes the need for you to shift the front chainring at all. It does it for you. Simply move up and down the rear cassette and at a certain point Di2 adjusts both your front and rear derailleurs to suit. It works well. Really well. Starting in your easiest gear you simply hit the rear derailleur ‘up shifter’ repeatedly and Di2 runs through?the entire gearing range without the need to manually change the front chainring.

In practice, I found that manual mode was, well, like usual. Semi Auto was neither here nor there and fully auto works really well. I am not sure how much I would want it if I was road racing, maybe I would like more control over when I changed the chainring but for everyday riding or time trialing/triathlon racing the full auto mode is fantastic. I now leave it on Auto (S3) mode all the time.

Some people may have to have their firmware upgraded in store in order to access these shifting modes.

To change the shifting mode:

Double click the junction box button and it runs through the shifting modes. Each time you double click it moves to the next mode. You can tell which mode it will be in by the number of times the red LED flashes.

  • 1 Flash – Manual (S1)
  • 2 Flashes – Semi Auto (S2)
  • 3 Flashes – Auto (S3)

Simply keep double clicking the junction box button until you see the number of flashes you need for that mode, that’s it. Nothing else required.

Thanks to the E Tube Project software you are actually able to map when and where the shift ion the chainrig happens, maybe overkill but might be useful for differing styles of course or riding. The three modes above come by default though.