I hit 28 mph on my Dax 70cc with a 40 tooth sprocket. I'm currently running 26 x 2.125 knobby tires. I'm planning to get some smaller hybrid style tires to hopefully reduce some drag. Other than this, the engine starts to vibrate quite a bit at 25 mph or more so I try to maintain a higher average speed rather than a top speed. By maintaining at least 20 mph, you can get places!