A spare tire body for the tire cavity of run-flat tires comprises: a plurality of circumferentially arranged combining blocks each being a hollow member that has two lateral sides each with a through hole, a bottom, two lengthwise ends on the bottom diagonally formed with projecting portions, and a top formed as an engaging valley; and either a) a C-shaped lining piece and two C-shaped holding pieces or b) a C-shaped lining piece or c) two C-shaped holding pieces or d) a C-shaped lining piece and one C-shaped holding piece. A connecting assembly of two pairs of fine tuning members, an adjusting member, a pressing bolt, a pressing screw bolt, and two reinforcing plates may be provided.