When I was ten years old or so, I rode a heavy steel single speed coaster brake Schwinn bike with big fat tires and had the mock gas tank in the frame (similar to Pee Wee Herman's bike). It had a round mechanical speedometer attached and when sprinting, it would register 40-45 mph. At ten years old, I didn't know better and believed it. Now I realize that I was probably doing 10-12 mph. I guess with the right speedometer you can think you can do anything.