Tutorial: Retrofitting Shimano Di2 Gearing to an Ebike with Bosch Smart System

Electronic gear shifting is becoming increasingly common on ebikes, especially on the more expensive models. However, if your ebike currently has mechanical derailleur gears, you don’t necessarily need to look for a new ebike. After all, you can switch from a mechanical derailleur to an electronic Di2 gear system from Shimano on an existing ebike. And it’s not as complicated as you might think. Using a KTM Macina Cross featuring a Bosch Performance Line CX as an example, this tutorial shows you how to switch over.

1. Shimano Di2 and Bosch: Which motors are compatible?
2. Automatic mode with Shimano Di2 also available with the first Bosch Smart System motors?
3. Starting point for retrofitting Shimano Di2 to the Bosch Smart System
4. Connecting the rear derailleur to the ebike system
5. Connecting the rear derailleur to the shift lever
6. Specifying the rear derailleur in the Shimano E-Tube Project app
7. Mounting the rear derailleur
8. Fine-tuning the rear derailleur
9. Selecting the cadence and preferred automatic mode
10. Retrofit kits for switching to Shimano Di2

1. Shimano Di2 and Bosch: Which motors are compatible?

Basically, all ebikes equipped with a Bosch e-drive of the third development stage, i.e., Smart System, are compatible with Shimano Di2 electronic shifting systems. The only restrictions apply to ebike systems with the following motors:

• Bosch Performance Line PX
• Bosch Performance Line, Gen 5
• Bosch Performance Line, Gen 3
• Bosch Active Line
• Bosch Active Line Plus

These five motors are designed in such a way that the chainring cannot rotate independently of the motor. Fortunately, this does not mean that none of the automatic modes of Shimano’s electronic gear systems can be used. However, they cannot implement the Rollshift function.

Speed pedelecs are a special case. Their motor, the Bosch Performance Line Speed, generally does not support any of Shimano’s automatic modes for derailleur gears.

2. Automatic mode with Shimano Di2 also available with first Bosch Smart System motors?

For a long time, it was believed that electronic shifting with a Shimano derailleur was not possible on older motors with the Bosch Smart System. We wanted to find out for sure, so we dug out a 2022 KTM Macina Cross CX with a mechanical derailleur. It was equipped with a fourth-generation Bosch Performance Line CX, i.e., from the first model year with Bosch Smart System. And lo and behold, the conversion to a Shimano Di2 was completely successful. After the change, all three automatic modes M, M+, and A could be used on this ebike.

3. Starting point for retrofitting Shimano Di2 to the Bosch Smart System

As already mentioned briefly, this tutorial refers to the conversion of a KTM Macina Cross 720, which already has some kilometers on the clock. In addition to one of the first Bosch Performance Line CX motors from the Smart System, the original equipment from 2021 includes the following shifting components:

• rear derailleur: Shimano Deore RD-M4120-10 SGS shadow
• shift lever: Shimano Deore SL-M4100-10 display
• cassette: Shimano Deore CS-M4100-10 / 11-42
• chain: KMC e10 EPT e-bike

Those familiar with Shimano’s nomenclature will recognize from the cassette designation that this model features ten sprockets and Hyperglide technology. However, Shimano’s electronic Di2 groupsets only feature Hyperglide in their 12-speed cassettes. Therefore, in this example, we have opted for the Shimano Cues Di2 groupset with the more robust Linkglide standard. The chain has also been replaced. As a result, the following components and parts have been used in the conversion:

• new Di2 rear derailleur: Shimano RD-U8050-GS
• matching shift lever: Shimano SW-EN605-R
• new cassette: Shimano CS-LG400-10 / 11-43
• new chain: Shimano CN-LG500
• Shimano connection cable: length 1 m

4. Connecting the rear derailleur to the ebike system

You can check whether the rear derailleur can be successfully connected to the ebike system right at the start of assembly. This way, you can make sure everything is working properly before you start the installation and avoid discovering that something is wrong when you are already in the middle of the conversion.

To do this, first connect the motor to the corresponding Shimano connection cable and the Di2 rear derailleur. First, unscrew the motor cover from the ebike. This will give you access to the various ports on the ebike motor. The connection cable is designed to fit into the yellow high-power port (HPP). If the slot on your ebike is already occupied—for example, by an ABS or a front headlight that requires two connections—you can use a Bosch Component Connector for the Smart System to create new HPPs on your ebike.

With the Di2 rear derailleur now connected, switch on your ebike to pair the rear derailleur with the system. To do this, first connect your ebike to the Bosch eBike Flow app. In the ebike settings and components menu, you can add the rear derailleur via the “Miscellaneous” tab. As soon as the pairing attempt starts, press the button on your rear derailleur for about two seconds until the small LED there lights up blue. The rear derailleur is now in pairing mode. If everything works smoothly, the eBike Flow app will recognize the rear derailleur and suggest pairing it. Confirm the request and after a few seconds the new rear derailleur will be connected to the Bosch drive. It will then appear in the component list for your ebike in the app.

Tip if pairing fails

If no connection is established between the rear derailleur and the ebike system, this may mean that the rear derailleur has already been connected to another ebike. In this case, simply delete the rear derailleur from the component list of the ebike in question. Then reset it to the factory settings on this ebike. To do this, press the button on the derailleur for eight seconds while it is connected to the ebike. The light will then flash green and red alternately. Then quickly release the button. After a final flash of the LED, it should be reset. Pairing with the new ebike should now work as described above.

5. Connecting the rear derailleur to the shift lever

To connect the rear derailleur to the shift lever, you need the Shimano E-Tube Project app. You don’t necessarily need to be logged into the app to start this step. You can skip this and press the large plus sign that appears on the welcome screen. Then press the pairing button on the rear derailleur for two seconds until it lights up blue. The app should then recognize the rear derailleur. A few seconds later, a message will appear telling you that you can register it. You can skip the prompt asking if you want to change the passkey if you wish. Changing it would provide additional security for access to the rear derailleur.

Next, the app will ask for a shift lever for the derailleur. The connection is made using the QR code. Press any of the three buttons on the shift lever to activate it. You can then scan the QR code on the back of the trigger and the rest of the pairing process will run automatically. If you want, you can now give the rear derailleur a special name in the app and save it together with a picture.

If you still have the rear derailleur connected to the ebike at this point, you can already test the shifting. Pressing one of the shift buttons should move the rear derailleur.

6. Specifying the rear derailleur in the Shimano E-Tube Project app

For derailleurs that are compatible with multiple cassettes, you can use Shimano’s E-Tube Project app to set which cassette is installed on the ebike. You will find the derailleur among the components connected to the ebike. Click on it and select the appropriate cassette gradation under “Cassette.” The system needs this information to execute the shifting processes cleanly and to position the rear derailleur correctly.

When you switch off your ebike, reactivate it, and the correct gear display appears, you know that the entire pairing process has been successful.

7. Mounting the rear derailleur

To mount the Di2 rear derailleur, we recommend switching off the ebike completely. It is also best to remove the battery. Your ebike is now completely de-energized, easier to move on a mounting stand, and you can access all cables and wires more quickly.

First, remove the old derailleur cable. Start at the shift lever. On the KTM model, the derailleur cable is routed throughout the ebike with a corresponding housing. This can remain in the frame. It will prove to be extremely useful in a moment.

Then remove the rear wheel. If you also want to replace the cassette during the conversion, now is the right time to do so. Please note that the cassette must match the freewheel of the rear wheel. Shimano offers two standards for freewheels: HG and Microspline. HG is suitable for cassettes with nine, ten, and eleven sprockets, while Microspline is suitable for twelve sprockets. If you want to be on the safe side, it is best to replace a cassette with one that has the same number of sprockets.

Old shift cable housing as an important tool

Next, open the chain and remove it. You can then remove the rear derailleur. To do this, loosen the screw on the rear derailleur and pull it completely out of the ebike. Now pull the Shimano connection cable from the motor to the rear derailleur through the frame of the ebike. You can make this step easier by using the remaining shift cable housing. Pull it from the handlebars through the frame so that it only extends from the motor to the exit point on the chainstay. Attach the Di2 connection cable to the end of the housing that is close to the motor using heat-shrink tubing. Now carefully pull the shift cable housing out of the frame at the end of the chainstay. At the same time, the connection cable will be skillfully fed into the frame.

The rest of the assembly is very straightforward. Mount the new Di2 rear derailleur on the ebike and plug in the Shimano connection cable. Once the rear wheel with the new cassette has been installed, you need to decide whether to continue with the new or the old chain. It is generally recommended to replace the chain at the same time as the cassette. If you know the required chain length, you can shorten the chain before installation. If you are unsure, it is best to work with the original length first. You can also shorten it when you try out the first gear changes with the new setup.

At this point, you can now plug the connection cable into the HPP of the ebike motor. After screwing on the motor cover, inserting the battery, and mounting the shift lever on the handlebars, your ebike is ready for its first tests. So switch on the ebike system and perform a few gear changes.

8. Fine-tuning the rear derailleur

To get the most out of electronic shifting, the rear derailleur must be adjusted precisely. Start by adjusting the upper and lower limit screws on the rear derailleur. The L-bolt prevents the chain from falling off the cassette when shifting beyond the largest sprocket. By adjusting the H-bolt, you can ensure that it does not get wedged between the cassette and the frame at the lower limit beyond the smallest sprocket.

Now for screw number three on the rear derailleur, the B-bolt. This regulates the distance between the top pulley and the largest sprocket on the cassette. The technical term for this is chain wrap. A mark on the back of some rear derailleurs helps you find the right distance.

To perfect the whole thing, open the Shimano E-Tube Project app again. Press and hold the mode button on the rear derailleur until the LED lights up yellow. This puts it in fine adjustment mode. You can now use the shift lever to move the rear derailleur to the left or right in millimeter and micrometer increments. Keep doing this until the chain runs smoothly and almost silently and the cassette can be shifted up and down easily.

9. Selecting the cadence and preferred automatic mode

You can set your preferred cadence in the Bosch eBike Flow app or directly on the ebike display. On the Bosch Purion 200, for example, press and hold the menu button. Use the right arrow key to access the cadence setting and select the desired value. Bosch has chosen to divide the settings into increments of five. The selected cadence serves as the basis for the Bosch system’s automatic mode.

You can select the exact automatic mode you want to use using the selection button on the Purion 200. In mode M for manual, you do all the shifting yourself. You get a little assistance in mode M+. Basically, you do all the shifting yourself in this mode too. The system only takes over when you are coasting. Thanks to the Rollshift function, the chainring continues to turn automatically and shifts to the gear ratio that best suits your current speed. In automatic mode A, everything is not only electronic, but also automatic. Depending on the stored cadence, the system automatically selects the appropriate gear ratio. It doesn’t matter whether you are riding uphill, downhill, on flat terrain, into a headwind, with a tailwind, or whatever.

10. Retrofit kits for switching to Shimano Di2

Meanwhile, there are numerous rear derailleurs, shift levers, cassettes, and other components available in Shimano’s Di2 universe. Keeping track of them all is not always easy. To make your selection a little easier, Ebike24 offers pre-assembled retrofit kits. Once you know which Di2 groupset you want to switch to—Cues, Deore, Deore XT, or Deore XTR—whether you want ten, eleven, or twelve gears, and whether you prefer a Linkglide or Hyperglide system, you can head in the right direction. The product description for each set also includes information on which cassettes the set is compatible with.

Pictures: Elektrofahrrad24 GmbH; Shimano Europe B.V.