I rented a car several years ago that had the mpg reading while you drive, and an average. I slightly over-inflated the tires and if going 38 mph, It would show ~60 mpg. (I never drove enough at that speed to do a true test, but a few years later, when I owned a car with that feature, it only over estimated by about 2 mpg). What was interesting was how much difference a rough road and smooth road made; a few miles per gallon less on a rough paved surface.
I rented a car several years ago that had the mpg reading while you drive, and an average. I slightly over-inflated the tires and if going 38 mph, It would show ~60 mpg. (I never drove enough at that speed to do a true test, but a few years later, when I owned a car with that feature, it only over estimated by about 2 mpg). What was interesting was how much difference a rough road and smooth road made; a few miles per gallon less on a rough paved surface.