I've done some research on this forum and some people claim that their HT bikes randomly kick into "turbo" mode and give them a super-boost while riding. One guy claimed he hit 40mph. I hit 40mph on my bike, that wasn't even fully broken in, on flat ground. It has 29" wheels, but I may honestly thinking that the engines they make recently are a little bit better than the first kits. Now that it's broken in it still does 40-45 on 25:1 gas mix, no upgrades. I've also had zero problems with that engine. I just don't like the manual clutch, the sprocket adapter, my Walmart bike... that build I did with an HT was really just a $200 experiment to tell me "Hey, this is really fun and addicting. And legal if you build it right". So now I'm selling that bike and building a custom 79cc predator bike. But I did notice on my sketchy rides of this bike that it was much faster than most I heard about on this forum. I used three methods to test speed. A gps, a bicycle speedo, and a car following behind.