There is provided, in a tire/rim assembly, in which hollow particles are filled in a tire chamber, in order to reform the surface of the hollow particles and to prevent the hollow particles from adhering with each other, in applying coating to the surface of the hollow particles, a method for even distribution of the coating on the surface of the hollow particles and the robust fixing to the surface.In a tire/rim assembly constructed by assembling the tire onto the rim, arranging a number of thermally expandable hollow particles consisting of a continuous phase of a resin and a closed cell(s) in the assembly and filling high-pressure gas exceeding an atmosphere pressure in the tire chamber, at least a part of a surface of the hollow particles has a coating fixed by heating the surface.