It has a lot to do with how high the engine revs, rear sprocket size, the levelness of your surroundings, hills consume much more gas, the greater the speed, less mpg. And the weight of the ride, which you already mention. I weigh 180 and have a 40T sprocket and live in a fairly level place, with some hills. I ride to the local stores and other places about a 5 mile round trip. I get around 65 to 70 mpg. I rarely go over 30mph.