I've kept diligent track of my 544T's fuel economy for years. Some of those years included roadtrips. Some of those roadtrips included segments where I arrive at a gas station with a known address (and fully warmed up), and drive directly to another gas station with a known address, with absolutely no stops or detours. I have at least three such segments in my records, all in different places, all of which show mileage on GoogleMaps to be 3.9-4.0% higher than what my odometer read for the same segment. Call it 4% since maps don't show fractions of a mile. All three segments were with 225/50R17 tires (25.9" OD, which is 2% bigger than stock 235/45R17 or 25.4").

Calculated and not including odo error, my lowest tank was 12.7mpg, which was mostly short trips in the coldest winter in that locale since the 70's. Next-lowest was 18.7. Highest was 23.5. Ignoring the winter tank, the mean is 21.5. Factoring in that 4%, it comes to a mean of 22.36.

Anyone else?