Originally Posted by
SlowerOne
The larger you can get both the spur gear and the pinion, the more efficient the drive. Large spur/pinion combinations allow more teeth to be in contact, so sharing the load and reducing the angles of approach and departure of the teeth. This is also what you see as Jason's 'freewheel' effect - it is a smoother mesh so it will roll better.
So lemme see if I got this right. If the larger gears roll better, then the car will maintain more momentum off power, requiring less throttle and energy to get back up to speed. Is this where the efficiency comes from?