I have tracked my mileage since I purchased my 2012 RT-S SM5 new last year. I posted a mileage chart for all my fill-ups (up to that time) online.
CLICK HERE TO SEE ALL OF MY MILEAGE
Maybe I was naive, but I didn't even think to ask about mileage before I bought my Spyder. My 1994 Goldwing was around 40+ with a 1500cc engine. I just assumed the Spyder would be better. But as other posters have said, 30/31 miles per gallon is pretty standard.
Yes, you will get someone saying, "I took a ride yesterday and I got 38 mpg" or something similar, but that is baloney. On a tank as small as 6 gallons, a small variation in how much gas you add to fill-up can make a tremendous difference. Go to fuelly.com and register and track all of your fill-ups. Only over time, can you learn your true average gas mileage.
HUGE differences in a single fill-up is probably based upon the tank not being filled properly. To be honest, if I try to fill the tank to quickly, the pump shuts off BEFORE it is properly filled.
I usually fill my tank when it is on empty and it probably still has a gallon+ in the tank if you believe the 6 gallon capacity.
Look at my chart - it will tell you the true story over time.
CLICK HERE TO SEE ANOTHER THREAD ABOUT GAS MILEAGE