Have never got 50 mpg on any of my Harleys when I did a mileage check over an extended trip.
Have friends that say they get 50-60 mpg on their Harleys, no idea if really they do or not. Know of one guy who will hit the kill switch going down a big hill to "save gas". Never cared that much about it myself, that seems strange/odd to me.
Depends on riding style, road geography (flat vs hilly), wind/ no wind, speed, etc. From experience the "mpg" calculators on most all vehicles are inaccurate. Fill up, figure miles since last fill up, and take the average mpg over 5-10 multiple fill ups is how I would check, back when I cared to check.