Abstract: The invention pertains to apparatus for inflating tubeless tires, particularly of large sizes, wherein the tire is quickly inflated, and a variety of wheel widths may be readily accommodated. A wheel and uninflated tire are located within the path of movement of an inflation head which includes an annular wheel rim seal ring which is brought into sealing engagement with the wheel rim. Thereafter, a tire sidewall engaging seal ring also mounted upon the inflation head compresses the tire sidewall under the influence of an expansible air bag motor to displace the tire bead from a sealing relationship with the wheel flange, and the sidewall engaging ring forms an annular compressed air receiving chamber with the wheel rim ring permitting compressed air to enter the tire throughout the displaced tire bead periphery.