The invention relates to a multistrip insert, usually comprising three strips side-by-side, for a pneumatic tire, said insert being composed at least in part of a closed cell resilient material constructed and dimensioned to fit ring-like about a wheel rim within the tire. The insert normally fills less than the whole internal cross-sectional volume of the tire but can support the tire against total collapse when deflated. In use, should the tire become deflated, the insert expands to fill or substantially so the internal volume of the tire due to the increase in temperature caused by the increased flexing of the tire and insert. The consequent return to or towards the normal operative tire shape results in the tire subsequently running at or near normal running temperature.