In Switzerland, the law authorizes you to ride a converted bike without registration (yellow moped plate) up to 500w motor power, and 25km/h assistance (this does not concern the authorized limit at which you can ride, you must respect the law on road traffic in all cases).
If you exceed the assistance limit of 25km/h or 500w motor power, you can only use your bike on private property.
If you wish to ride your bike on a public road with a motor exceeding 500w or 25km/h, you must have your bike inspected by the motor vehicle department of your canton of residence. Before making such a purchase, please contact the motor vehicle department of your canton of residence for further information.
Here you'll find a list of permitted regulations for electric bicycles.
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German: Download memento