I run a 125 cc 2 stroke KTM dirt bike on the street. It is capable of over 140kph maximum speeds and sustained 120kph depending on sprocketing. You cannot just put the highest ratio on and expect good performance. Typically you have to experiment to have the maximum power arrive at the highest achievable speed. Any higher ratio lowers maximum speed and kills 1st gear performance. The 2 strokes especially are very susceptible to carb jetting. My initial highway fuel mileage was only 27-35mpg(imp) with the stock jetting. The 2 stroke would not my first choice for fuel mileage, but does prove you can still ride a small displacement bike on today's streets. Current fuel mileage is only about 55mpg(imp) maximum.
