my bosch mid drive bike has enough resistance with 1.5" tires. it feels like a slug with no power but that could just be me. I think the fat tires are just cheaper and easier to do and you can get away with less bike sizes and and the tires take care of some of the harshness on a cheap bike. I get a kick out of this guy who looks about 6' perched on top of one of the 20" folders got to make bike handling worse. but he also goes through red lights so there is that.