Can anyone tell me how much fuel Harley's 5 gallon tank really holds? I routinely run mine down to where reserve says I have 20-30 miles left with the fuel gauge on empty and then can only put in 3.5 to 3.7 gallons before reaching the 'full' point in the fill tube which may be 2 inches below the fuel cap. This, with the bike on the side stand - just a typical fill up. Is 5 gallons an absolutely full, running over the brim, fill-up? I have a distinct feeling that when I think I have a full tank of gas I really have less than 5 gallons. Just curious about the 'truth in advertising' vs. real world fill-ups.