Runflat tire

Runflat tires are generally made by including a stiff insert in the sidewall thereof. This insert should be as stiff as possible to help support the weight of the vehicle to which the tire is mounted in situations where there is a loss of air pressure. However, the material used in making the insert should also exhibit low hysteresis and must be processable. This highly beneficial combination of properties is attained by utilizing the compositions of this invention in making inserts of runflat tires. This invention discloses a runflat tire which is comprised of a generally toroidal-shaped carcass with an outer circumferential tread, two spaced beads, at least one ply extending from bead to bead and sidewalls extending radially from and connecting said tread to said beads; wherein said tread is adapted to be ground contacting, wherein said sidewalls contain at least one insert radially inward from said ply and wherein the insert is comprised of (1) a cured polydiene rubber that is coupled with a Group IVa metal selected from the group consisting of tin, lead, germanium and silicon, (2) from about 30 phr to about 130 phr of a filler and (3) from 0.1 phr to 5 phr of a fatty acid. The insert will generally extend radially inward from under the outer circumferential tread toward the bead to which the sidewall extends. It is normally preferred for the cured polydiene rubber to be coupled with tin.