Even with a small tank I can get 120-130 mpg. One way to do this with your bike is....carry a 1 gall. can of gas with you on a trial run, go all the way on a full tank, check the mileage when you need to switch on reserve, continue til you run completely out of gas (check mileage again). Refuel with gas from can to take you to gas station. This way you´ll know precisely what your own bike will do.