My ebike maxes out around 1400W -- that's an actual measurement made with a power meter -- and the fastest speed I've ever seen is 56km/h (and that was with a t

My ebike maxes out around 1400W -- that's an actual measurement made with a power meter -- and the fastest speed I've ever seen is 56km/h (and that was with a tailwind). And this is with relatively fast tires (not racing tires, but smooth road tires) and a big fairing! Given the same tires and aerodynamics, the difference in top speed between 1400W and 1800W is the cube root of 1800/1400, or 1.087 -- you can go 8.7% faster. That gets you to 61km/h. And I bet your aerodynamics and tires are both worse than mine. So something is out of whack here. My guess is it's a combination of things. Most speedometers in cars read high, many by as much as 10%. So let's say you were really doing 72km/h. Maybe with a full battery you're really getting quite a bit more than 1800W. For my bike to do 72km/h would take at least (72/56)^3 * 1400W = 2800W. It sounds a bit unlikely that you could really get that much, but who knows, it depends on your controller and motor. (You'd think they would have rated it higher, though, if it could really do that.) To really get 80km/h would take over 3800W.