A runflat system for a motor vehicle, comprising a non-standard one-piece rim having at least a first peripheral cavity or drop center to enable a tire to be mounted on the rim, and a runflat device for mounting on the rim inside the tire, said device being constituted by a rigid ring split into at least two circularly arcuate elements or sectors, wherein the rim has at least one second peripheral cavity which is separated from the first cavity by an intermediate peripheral ridge, wherein each sector of the ring has a radially inner portion for being received in the second cavity of the rim, and wherein the system also comprises means for fixing the sectors in the second cavity of the rim.