I've been experimenting with the mileage on my '07 Royal Star. I use 93 octane, synthetic oil, and I have K&N air filters. I get 38 - 42 mpg at 65 - 70 mph. If I slow down and really take my time on the flat roads of Florida not exceeding 55mph. I get 52-53 mpg. I can not believe the difference. However it is difficult fighting the urge to roll on the throttle. That is half the fun. But if you are not in a hurry and want to enjoy the ride..... slow down and see for yourself.