Earlier quoted context omitted.
1800 watts isn't nearly enough to do 80km/h. Maybe 60km/h, tops. Power goes as the cube of speed, so 80 takes more than 4 times as much power as 60. Of course, your speedometer could be lying to you.
We tested it with a car and another motorbike. It can only do that on a full charge and the bike shakes a bit too much for comfort. But traffic in Saigon rarely goes above 30km/h anyways. When I have free charge of the road, I average about 55km/h.
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.