A hub electric motor unit for a motor-driven or motor-assisted vehicle, the vehicle comprising a frame, a wheel having a hub and a wheel rim connected to the hub by a plurality of spokes; the hub electric motor unit comprising a shaft connectable to the frame of the vehicle, a stator unit mounted on the hub shaft, a rotor disposed around and coaxially with the hub shaft; a hub shell rotatably mounted on the hub shaft, wherein the hub shell comprises two cap members axially disposed on respective sides of the rotor; wherein each cap member comprises a connecting part for connecting a respective subset of the spokes.