The disclosure is generally directed to a wheel-mounted, centrifugally activated, air compressor that will automatically inflate an inflatable vehicle tire back to the proper pressure level when small under-inflation situations occur (e.g., the occurrence of small-to-medium air leaks in a tire). Moreover, the device can be easily attach or fitted into the design of a steel or aluminum wheel, or fitted into a hubcap without modifying the standard design of the wheel-hub assembly. The wheel-mounted device includes a mounting base, cylinder assemblies, and spring-biased centrifugal arms, and is designed to convert changes in the centrifugal force felt by the centrifugal arms as wheel rotation accelerates or decelerates/stops into varying force exerted on positive-displacement pistons. This in turn actuates positive-displacement pumping action at the cylinder assemblies, each of which can provide a short burst of pressurized air into the charging line connected into the associated tire with each compressive stroke.