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 .