A run-flat insert or safety roller for inflatable tires comprising a plurality of arcuate members which, when clamped in end to end relation circumferentially envelop the wheel or rim in a manner to rotate therewith in normal operation but to slip circumferentially thereof when riding on a deflated tire, is provided with circumferentially engageable lock means permitting partial assemblage of the insert within a tire in advance of mounting the tire on a wheel or rim and completion of said insert assemblage, to circumferentially envelop said wheel or rim, by application of radially opposed forces to outer surfaces of the mounted but uninflated tire.The circumferentially engageable lock means enables the run-flat insert to be clamped to the rim by novel procedures compatible with existing automatic tire mounting equipment of automotive assembly lines. Strategically located apertures adjacent ends of the arcuate members, and receiving leverage members extending perpendicularly to the plane of the arcuate members permit the tire bead to be pried to the side, thereby providing access to the joint, to provide manual closing of said lock means when desired.