Motorcycles use chain drive and a clutch. Isn't a bicycle with a chain driven engine just a cheap motorcycle? No offence intended, I'm new here, but I avoided using a chain drive on mine and stuck with the rubber wheel on the tire. There's all types and kinds of motorized bicycles, I know, I'm not against how you make the pto work. To me the only requirement is that it will get you up a steep incline (hill) without pedaling. In my area if you have a chain drive you're going to get stopped for driving a motorcycle without the proper paperwork. They leave you alone if it's rubber to rubber pto.