what's the mpg? if you have to ask that question it is not for you. I know - 146mph into a 10mph headwind, 3500' elevation, flat road surface, girlfriend on the back, light luggage, cruise control on = 11.2mpg
Those big motors dont need to work very hard at normal cruising speeds. I think that that is why they can potentially get good mileage if you are easy on the throttle. I would not worry about the mileage nearly as much as I would worry about the rear tire. I could see myself smoking the rear tire 1st thru 3rd gear a lot and hoping to get 3000 to 4000 miles out of a tire.We have injected 124"ers that clients have reported back to us that they are north of 50 mpg, under normal riding conditions.