Is tuning permitted?

No, tuning is not permitted.
Using a tuning kit or manipulating your Bosch eBike system in any other way will risk invalidating your warranty and guarantee entitlements for the Bosch eBike system and other bike components. Moreover, improper use of the system generally reduces the service life and you risk damaging the drive unit and the bike itself. You may also endanger your safety and the safety of other road users as well as incurring high personal liability costs and even criminal prosecution as a result of accidents attributed to tuning. Bosch eBike Systems therefore asks that all riders and providers refrain from tuning eBikes.