A semi-pneumatic tire assembly including a tire casing 22 and a lining 26 is provided. The lining 26 includes a contoured inward surface 30 defining an inflation chamber 18 about an associated wheel rim. The tire assembly is formed by injecting a curable, lining-forming material 96 into a cavity 57 defmed between the tire casing 22 and a molding member 50. The molding member 50 includes a contoured outer surface 54 which molds the inward surface of the lining 26. The molding member 50 may be an inflatable airbag 100 retained in the tire assembly during service. Alternately, the molding member 50 may be a solid core 114 which is removed prior to mounting the tire casing 22 and lining 26 on the associated rim.