I find it disgusting my Goldwing weighing in at around 800 pounds gets lower fuel mileage than my 3300 pound TDI Jetta. I have managed 53.6 mpg U.S. out of that Jetta running 65mph before though.
Best fuel mileage on my Goldwing was about 47 mpg running about 45-55 mph, I average about 39 mpg..
Fuel summary of ~4500 mile 11 day trip.
3 bikes - '07 DL650, '03 VTX1800, '04 GL1800
We did not ride easy.
avg fuel mileage on the trip for each bike -
50 mpg DL650
44 mpg GL1800
40 mpg VTX1800
The all time avgs for each bike are slightly higher.
On a couple 150 - 175 mile stretches at 70+ mph with a headwind, the goldwing got slightly better fuel mileage than the 650 - 40 vs 39. The VTX 36.