Unfortunately, there's no one rule for the location of the motor on an electric bike. The position can change the feel of the ride and the maintenance requirements. Ideally, however, you want the weight balanced across the whole frame. Front-drive is best for city riders spending the most time on flat, smooth surfaces. On the other hand, rear-drive is suitable for mountain bikers, so the weight is at the back, allowing maximum maneuverability of the front wheel.