With all my crazy add ons and mods, I get 12-14ish around town, 17ish on the highway. I would guess OEM tires, lose the roof rack (that costs me a solid mpg), neutral when at lights (thanks Rif for that one, think how much you have to hold the brake when sitting, all that energy is gone while in neutral) windows down at low speeds, ac at higher speeds, etc...I got 21 mpg on my trip with her when I drove from Columbus, Oh to Charleston, SC. That was bone stock with bad wheel bearings, bad ac compressor bearings, no exhaust.
That is why we have a brand new ford fusion for running around town, my wife's trooper RS does much better on mpg around town, but about the same on the highway.
Good luck with the mpg, those motorized bikes are nice, my parents have some for their RV.