Hi,Matt! I think if you read the ad carefully on the Carr precision,or maybe it's another one I've read,that the 300mpg is contingent upon how much you pedal to assist that engine.If I'm wrong on this,I apologize.Also,one thing I've heard about bikes that you motorize is that they're the devil to get stopped when traveling at 30mph+.That's a safety mod. you might want to think about doing also.BYE!