Abstract: An electric motor operated wheel that contains the electric motor, the batteries and battery carrier, and controller in an area between the rim and hub of the wheel. These components are enclosed by a rotatable disk that spaces the rim from the hub and integrally connects them and a fixed cover disk disposed on the opposite side. The construction is such that the axial width of the wheel driving components is not substantially greater than the width of one of the hub and the rim. The electric motor drives the wheel through a flexible transmitter transmission, including a tensioning mechanism that maintains a tension on the driving belt that is related to the driving load.