Synchronized Shifting is a huge subject, and if you'd like to know more about that I recommend reading my complete guide to synchronized shifting.
Short on time? Here is the quick summary.
Modern Di2 bikes have three different shift modes: manual mode, shift mode 1 (usually semi synchro), and shift mode 2 (full synchro).
In semi synchronized mode the rear derailleur will automatically shift to compensate for front derailleur shifts.
In full synchronized mode, the front derailleur shifts automatically as the rear derailleur reaches certain gears. This is great on TT/Tri bikes.
Change selected shift mode
While you can use the E-Tube Project apps to change what each shift mode does, that doesn't actually change the selected shift mode on the bike.
To change the bike to the next shift mode, press the function button twice. The LED will then indicate the selected shift mode.
On 12-speed bikes, the button and LED are on the rear derailleur. This is what the LEDs mean:
- Blue (2 seconds): Manual shift
- Flashing blue (2 times): Shift mode 1
- Flashing blue (3 times): Shift mode 2
Read more on Synchronized Shifting in the complete guide to synchronized shifting.