If you need to exceed 30 mph, then you need to get a scooter or motorcycle and not a motor assisted bicycle "MAB". I feel we should be good stewards for our transportation and hobbyist alike and we really need to be careful when riding . Making or souping up a bicycle to go 40 plus mph will get you trouble and will set a bad example for others that do have a bicycle with motor assist. If you want to go 40 or 50 mph, you really need to get a scooter or motorcycle. Those are common attributes for scooters and motorcycles. The Axiom here is that any bicycle with motor assist that can go 40 plus mph is just not a good thing as it violates federal law for bicycles with motor assist to still be defined as a bicycle. From what I read, less than 49cc and 30mph on level ground under power is the rule. Most bicycle engine kits can go 30mph right out of the box and is plenty fast. Typically faster than traffic in the city, way faster than traffic in rush hour. Enjoy the ride...