A tip for Radwagon version 3 (26 inch tires). Please retighten all spokes after one year. For me after 2.5 years with the rear wheel: one spoke is missing completely, the other was still attached to the engine. Since there are large luggage bags hanging on both sides, this was stupidly overlooked. Driving got rocky. Replacement is available on Ebay. There are providers here who offer the length of 165 mm. It costs 36 pieces under 19 euros without tax (as of 2021).
The thread of the spoke has a length of 10mm. For better assembly, the thread can be shortened with a hacksaw. First screw on a threaded nut so that the thread with the nut is formed again after sawing.
Important - this length is only valid for version 3. The wheel of version 4 is smaller, please make sure that the length is correct.

(The text was translated with Google Translator)

Version 3 is the best for me. The motor consists only of coils and magnets, so there is no wear and tear on plastic gears in the motor! Due to the large engine power, insurance is mandatory in Germany. Only costs around € 25 a year.