45 kph flat out, if you try to go faster you are fighting the motor. But practically you're going to top out at about 40 kph on the Bosch system, using a Stromer or a Klever s-pedelec you will be able to maintain that 45 kph a lot longer. But 38 is plenty for me, it's still a bike and the little bit of extra speed does not weigh up against the risks.