Mastering Shimano Di2 shifting
Updated: 5 days ago
The Shimano Di2 (Digital Integrated Intelligence) system brings electronic shifting to a new level, offering precise, customisable gear changes. But what really sets Di2 apart are the various shifting modes it offers: manual, semi synchronised (semi automatic), and full synchronised (automatic). These modes allow cyclists to either take full control of shifting or let the system assist in optimising shifts for smoother rides.
What is Shimano Di2 Synchronised Shifting?
Synchronised Shift refers to Shimano’s automatic shift modes within Di2 systems. Contrary to what some may think, Synchro Shift is not one mode but actually two distinct modes: Semi Synchronised Shift and Full Synchronised Shift. Each mode is designed to work differently, but both aim to optimise gear transitions for an efficient, seamless ride.
Semi Synchronised Shift (Default: S1)
In Semi Synchro Shift when you shift the front derailleur, Shimano Di2 automatically adjusts the rear derailleur to compensate. This prevents sudden, large changes in gear ratios, which can disrupt your pedalling rhythm. For example, if you downshift the front derailleur, the system will move the rear derailleur one or two gears to smooth out the transition.
This mode doesn’t automate front derailleur shifts like Full Synchro, but it reduces the jumps between gears, making it easier to maintain a steady cadence.
When to use Semi Synchro Shift: Moderate climbs or rolling hills: When front derailleur shifts are necessary, but you want smoother transitions between gears.
Rides with frequent gear changes: This mode makes shifting more intuitive and easier without fully automating the process.
Benefits: Reduces drastic gear jumps by compensating rear derailleur shifts when the front is adjusted.
Ideal for riders who want to keep control of the front derailleur but still benefit from a smoother shifting experience.
Full Synchronised Shift (Default: S2)
In Full Synchro Shift, Shimano Di2 automatically shifts your front derailleur when you make certain shifts on the rear derailleur. This ensures the derailleurs work together to maintain the best gear combination for the terrain.
According to Shimano, Full Synchro Shift doesn’t monitor your speed or cadence - it simply follows a predefined map of shift points. For instance, as you move through the rear cogs toward larger gears (e.g., from 11T to 28T), the system will shift your front derailleur from the big chainring to the smaller one between certain gear thresholds, like 21T to 25T. This shifting map can be customised according to your preferences.
When to use Full Synchro Shift:
Endurance rides: Ideal when you don’t want to worry about manual front derailleur shifts.
Rolling terrain: Allows you to focus on the ride.
How to Check Modes
When you press a shifter button, your Shimano Di2 system shows two readouts in sequence: first the battery level, followed immediately by the current shift mode.
Battery
You can check your battery at any time by pressing and holding any shifter button for about 0.5 seconds. Look at the LED on your junction box (11-speed) or rear derailleur (12-speed):
Solid Green: 100% to 51% charge remaining. Typically lasts 1,000 to 2,000 kms.
Flashing Green: 50% to 26% charge remaining. You still have roughly 250 to 500 kms.
Solid Red: 25% to 11% charge remaining. You have an estimated range of 250 to 500 kms and you should charge it soon.
Flashing Red: Less than 10% charge remaining. You have less than 50 kms to 100. Charge immediately.
Shimano Di2 is programmed to protect your system and prevent you from getting completely stranded. If your battery drops too low, it shuts down components in stages:
Front Derailleur Shuts Down First: When the battery drops to around 10% to 5%, the front derailleur stops working. It will automatically move to the small chainring and stay there.
Rear Derailleur Shuts Down Last: The rear derailleur requires much less power to move. It will continue to shift for several hours after the front derailleur shuts down, giving you enough gears to get home safely.
If you are using a 12-speed wireless system, the small coin-cell batteries in your shifter hoods are separate and last about 1.5 to 2 years.
Shifting Modes
To check your current shift mode, you must double-click any shifter button (either the front or rear shifter) or via the function button on modern 12-speed rear derailleurs.
The system will then light up to show your battery status first, followed immediately by the shift mode indicator light.
12-Speed Di2 Systems
On 12-speed systems, the indicator light is located directly on the rear derailleur.
Look at the small LED on the rear derailleur after double-clicking your shifter or pressing the button on your rear derailleur:
Blue light stays solid for 2 seconds: Manual Mode
Blue light flashes twice: Shift Mode 1 (Semi-Synchro)
Blue light flashes three times: Shift Mode 2 (Full Synchro)
11-Speed Di2 Systems
On 11-speed systems, the indicator lights are located on your Junction A box. This box is typically strapped under your handlebar stem, tucked inside your handlebar bar-end, or built into the down tube of your frame.
Look at the red and green LEDs on the Junction A box after double-clicking your shifter:
Red and green lights stay solid for 2 seconds: Manual Mode
Red and green lights flash twice simultaneously: Shift Mode 1 (Semi-Synchro)
Red and green lights flash three times simultaneously: Shift Mode 2 (Full Synchro)
How to Change Modes
12-Speed Di2 Systems
Use the function button located directly on the rear derailleur body next to the charging port.
Double-press the button on the rear derailleur quickly.
The LED will flash blue to show your new mode:
Flashing Blue (2 times): You have switched to Semi-Synchro Mode.
Flashing Blue (3 times): You have switched to Full Synchro Mode.
Solid Blue (for 2 seconds): You have switched back to Manual Mode.
Keep double-pressing the button to cycle through these three settings until you reach your preferred choice.
11-Speed Di2 Systems
User the button is located on your Junction A box (found under your stem, inside your handlebar bar-end, or built into the frame frame tube).
Double-press the button on the Junction A box quickly.
The red and green LEDs will flash to show your new mode:
Flashing Red/Green (2 times): You have switched to Shift Mode 1 (Default: Semi-Synchro).
Flashing Red/Green (3 times): You have switched to Shift Mode 2 (Default: Full Synchro).
Solid Red/Green (for 2 seconds): You have switched back to Manual Mode.
Keep double-pressing the button to cycle through the options.
Pro-tip for customising modes
By default, Mode 1 is Semi-Synchro and Mode 2 is Full Synchro. However, you can completely re-program these modes using the official Shimano E-TUBE PROJECT app.
For example, you can change Mode 1 to drop 3 gears instead of 2, or turn both Mode 1 and Mode 2 into different styles of Semi-Synchro shifting.
We hope this explains how Shimano Di2 works and when to use them. If you still have questions or problems with your derailleurs or shifters, please give us a call or bring your bike in.
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