Runflat insert for tires and materials therefor

A runflat insert for enabling a vehicle to run on a deflated tire, mounted in an assembly comprising a pneumatic tire and a wheel rim, said insert being mounted inside the air cavity of the tire and secured to the wheel rim, said insert comprising:

• a) an elastomeric outer contacting portion for contacting the interior surface of the tire during deflated operation of the tire,
• b) a reinforced annular band disposed radially inward of said outer contacting portion, wherein said band comprises an elastomeric shear layer, at least a first membrane adhered to the radially inward extent of said elastomeric shear layer and at least a second membrane adhered to the radially outward extent of said elastomeric shear layer,
• c) at least one sidewall portion extending radially inward from said contacting portion for connecting said annular band to a base member fitted around the wheel rim for securing said insert to the rim, and
• d) at least one carcass layer adhered to said annular band, and said carcass layer extending radially inward from said annular band and anchored in said base member, wherein the shear layer comprises an elastomeric composition having a metal salt of a carboxylic acid, and wherein the carboxylic acid is selected from the group consisting of unsaturated carboxylic acids.