Embodiments of the present disclosure are directed to a rotor assembly for use in a radial flux electric motor assembly having core magnets rotatable relative to end magnets such that the torque constant of the rotor assembly varies. The plurality of end magnets is positioned over the core magnets when the rotor assembly is at rest and the rotor assembly has a first torque constant at rest. The plurality of end magnets can rotate relative to the core magnets upon application of torque to the rotor assembly.