Thank you for getting back to us and providing the requested information yesterday regarding your eBike.
Based on the current information given, this particular GEN4 Performance Line Speed drive unit is only designed for 28 mph and cannot be reprogramed to a 20 mph configuration.
Bosch designs and supports OE manufacturers with drive units to meet class 1 and 3 requirements set by local and federal laws.
The bicycle manufactures will equip their eBikes according to their specific needs and set their parameter requirement based on the model.
As mentioned above we cannot change the software within the GEN4 Speed Line drive unit to 20mph, however there is the possibility to make changes using the new Premium Function Nyon custom riding modes. I believe your current bike is equipped with the Kiox from what I saw on the Cannondale website.
For this to be possible, you would have to upgrade to the new Nyon display head unit (to be installed by a certified Bosch dealer) and download our eBike Connect App to your phone, unless you have this already, then there is no need to download.
If you have the app go to More → Shop, to purchase Nyon Premium Function.
The Premium Function allows you to set custom ride modes within the system to change motor support as well as speed. This will allow you to go from 28mph to 20mph. The App will be able show the setting if stopped. Unfortunately your bike will still be labeled a Class 3 bike.
We hope this was helpful and if you have any other question regarding the Nyon display or the eBike Connect App and Premium Function Nyon custom riding modes you can go to the provided link below for Nyon. You can also contact your local Bosch certified eBike dealer for any question you might have and reach out to us as well.
https://www.bosch-ebike.com/us/products/nyon
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