ok 1st there is no Motor that can be both a drive motor and a generator. They just don't build them like that. 2nd If you put a 250watt non-geared motor on the generator wheel you would still not get enough power out of the generator motor to power the drive motor. To much loss in drag, load, hills, Wind and your weight. No free lunch here.

Now if you put a Gas generator of say 1000 watts at 110v AC. then you could power the hub motor and/or charge the battery. The weight and size of the AC generator will not fit a reg bike frame. But you could get around 180 miles per gallon if you could. One guy on here did just that on a powered 4 wheel bike/car thing.