Hi there! I'm brand new to this forum, but I have first hand experience with riding a motorcycle thinking that I would get better fuel economy.
At best my 2001 1.0L Triumph Speed Triple got 40MPG. I crashed it once breaking my Right Arm, and the MCL and ACL in my right knee. It ran through a set of tires every 3000miles. Plus it had no cargo room at all. But it was a lot of "fun"!
I sold it and bought a 1999 Chevy Metro 1.0L. I'm now getting 44MPG. I can go to the store and get a couple bags of groceries and I can drive in the winter. Not much "fun" though.