A system for air injection into tires, comprising a rotary air chamber secured to a hub cap wherein the rotary air chamber is configured to inject air into at least one tire when tire pressure drops below a first adjustable preset value and to release air from the at least one tire when tire pressure rises above a second adjustable preset value, an air shaft extending through the hub cap and into the rotary air chamber, an air line attached to the air shaft, and ball bearings affixed between the air shaft and the hub cap. A bracket can be fastened to the hub cap such that the rotary air chamber is fastened to the bracket. The hub cap and air shaft are fastened to the axle such that an air line extends from inside the axle through the air shaft to the rotary air chamber.