of a singular material however it is within the scope of this invention to have the singular insert formed of multiple materials such as that disclosed in u s pat no 6 453 961 other insert configurations as well as other belt carcass bead portion and apex configurations are within the scope of this invention the rationale behind the construction of the modified impermeable inner liner is as follows during experimentation it was determined that the nature of the inner liner has a significant impact on the performance of a tire for a conventional non runflat tire the liner is the fifth largest contributor out of eleven tire components towards rolling resistance characteristics and is the third heaviest component in the tire while for a runflat tire the liner 39 s contribution is not as great it is still greater than the majority of other tire components because of this factor the inventors investigated the effect of the inner liner on a runflat tire tires as described in table 1 were built and tested to determine air permeability characteristics of runflat tires in addition to the inner liner construction described in the table each tire had the following common construction features a single runflat insert in each sidewall an apex two steel cord belts a spiral overlay a tread and a single rayon carcass ply construction construction construction construction 1 2 3 4 inner liner shoulder to bead to bead not present shoulder to construction shoulder shoulder in the toe area insert liner bead to bead not present bead to.