im thinking unless you made it real long and low then it might just to wheelies and flip over backwards.. and if it didnt... well then you need more power
secondly im 99% sure that you will need downforce, firstly to stop the car/bike get airborne over jumps and secondly so it can go around the corners faster.. and its difficult to get good downforce on a bike...
thirdly dosent a bike technically break the rule where the body must have some kind of "cockpit" area???