A method for making a polyurethane elastomer tire fill composition wherein a mixture of a) a low functionality (2.0-2.3) 4,4'-diphenylmethane diisocyanate, such as a carboiimide-modified (2.0 functionality) 4,4'-diphenylmethane diisocyanate and b) a nonreactive diluent, such as an oil extender, is mixed with a polyol, such as polypropylene oxide triol. The reaction mixture is inserted into a tire casing under pressure and cured therein to form an essentially void-free tire filler. The tire fill composition maintains pressure within the tire during use and has excellent physical and thermal properties. No prepolymer step is necessary in the method.