Heat-expandable microspheres and hollow fine particles and method for producing the same as well as tire/rim assembly

A tire/rim assembly, characterized in that a tire is assembled onto a rim and a great number of hollow fine particles are arranged in a tire compartment defined by the tire and the rim, and further a high pressure gas exceeding the atmospheric pressure is filled in the tire compartment,

• wherein the hollow fine particles each consist of an outer shell made of a thermoplastic resin obtained by polymerizing a monomer component in the presence of a polymerization initiator, and a foaming agent encapsulated in the outer shell and having a boiling point not higher than a softening point of the thermoplastic resin,
• the polymerization initiator comprises a peroxydicarbonate as an essential component,
• the foaming agent comprises a fluorine-containing compound having an ether structure and a carbon number of 2-10 and containing no chlorine atom and bromine atom, and
• a pressure in a hollow portion is not lower than the atmospheric pressure.