[Dirt_McGert]

Drag (wind resistance) plays a large part in fuel economy - the more drag, the more fuel you need to keep operating at a certain speed. Weight plays a large role too. However, so does engine size and engine speed (RPM.)

"One last thought, the N250 produces maximum torque at about 8,500 RPM. Someone may want to clarify, but I believe this is the most efficient operating speed of the motor. If you gear your bike to cruise at 8,500 RPM you'd be maximizing your fuel efficiency to a certain degree."

Hmmmmmm... It may be producing maximum power and torque at 8,500RPM, but the engine is also guzzling fuel to keep the crankshaft spinning that fast. It'd be like keeping the throttle maxed all the time in 2nd gear going 25mph on your bike or in 1st gear in your car. The engine speed wouldn't be matching road speed - you don't need that much power and torque that 1st or 2nd gear would give if you're travelling say 40mph.