This paper proposes the design of a novel weighted-rotor energy harvester, which oscillates due to the periodic change of the tangential component of gravity, to harvest kinetic energy from a rotating wheel. Unlike traditional energy-harvesting devices, which have a fixed natural frequency, when the speed of the car increases, the centripetal acceleration of the rotating wheel also increases the rotor's natural frequency of oscillation. By employing a suitably-designed weight, the natural frequency of the rotor can match with the rotating frequency of the wheel at any speed, and the rotor oscillates at a large angle and angular velocity to generate a large amount of power. The models of power generation were derived by using Faraday's law of induction and Lorentz force law, which were followed by the numerical simulation performed to verify the correctness with experiments. The output voltage and power have been discussed considering the constant and accelerating plate rotation speed. When a 550 ohm resistor connected in series, the average output power is 399 to 535 micro-Watts at plate rotation speed from 300 to 500 rpm and is possible to be the power source for TPMS.