Run-flat tire and method of making same

A run-flat pneumatic radial tire having a casing with a tread portion in the crown thereof, sidwalls extending from said crown on either side to annular bead portions on the inner periphery on each side of said tire, said beads being adapted to mount said tire on the rim of a wheel, tensioned annular belt means in said tire crown radially inwardly of said tread portion, a resilient annular compression element of high strength material comprising a helical coil, the coils of which are adjacent one another in a stressed condition, bonded, as an added stage in the course of building the tire or as a retrofit operation on an existing radial tire, inside said casing on the inside surface of the crown thereof radially inwardly of said tread portion, said sidewalls having therein a multiplicity of closely spaced substantially radial spoke-like reinforcing elements cooperating with said compression element, said radial elements having freedom of shear with respect to one another and being connected to said beads and extending therefrom to at least the crown region of said tire, and wherein inflation means inflated inside said helical compression element prior to the bonding thereof to a pressure approximately twice the normal operating pressure of said tire has been used to prestress said helical compression element to cause the coils thereof to have relative movement with respect to one another whereby the circumferences of said compression element and said inside surface of said tire crown are expanded to greater than their normal diameter at normal operating pressure so that a prestress is transmitted to said belt means, said prestress being locked in when said compression element is bonded, wherein said tensioned annular belt means act as a supplemental structure with said stressed compression element to increase the load-capability thereof in the run-flat condition of said tire.