I have the nearly the same experience on my 500, just a hair less. I'm running a tall windshield, weigh 260 lb, and live in the flat lands. Wind resistance (speed) will eat power (fuel)! Do some bicycle riding and you'll intimately understand this. :wink2:If I do a lot of highway riding I tend to be in the high 50's. If I do a mix of both I am at around 60. If I do mostly city driving I get upwards of 65+.
Lowest I have gotten is 55mpg and the highest is 68. Really depends how you ride!