The study investigates the planar vibration modeling of a radial tire with a large flat ratio for a heavy load vehicle. A proposed tire model with a flexible belt on an elastic analytical stiffness foundation is investigated via the theoretical modeling，experimental modal analysis and the parameters identification. The Euler beam model specifically assesses the circumferential vibration of the flexible belt，moreover the influence of the inflation is discussed. The analytical multi-stiffness function of a large section ratio sidewall is derived by combining the membrane feature caused by inflation pressure and the structural deformation caused by sidewall curvature. Additionally，the parametric identification of the proposed tire model is discussed. The experimental and the theoretical results indicate the following：（1）the bending characteristic of the belt within 0~180 Hz can be featured with the flexible belt on an elastic analytical stiffness foundation tire model；（2）the multi-stiffness function of the curved sidewall assesses the pre-tension membrane feature and structural deformation，which is related to the inflation pressure，structural curvature and material properties；（3）the inflation pressure affects the pre-tension force of the belt and the pre-tension membrane feature of the sidewall.