Abstract: Mechanical characteristics of run-flat tire under zero-pressure conditions are the basis of improving the driving performance of tire and realizing the stability control of vehicle blowout. Insert supporting run flat tire (ISRFT) is a typical safety tire based on pneumatic tire structure. As this type of safety tire has the advantages of simple structure, convenient disassembly and good zero pressure bearing capacity, it has become a new type of safety tire with great development prospect. With the improvement of vehicle performance, the performance of insert supporting run flat tire is also put forward higher requirements. The traditional insert structure is made of heavy materials such as metal and rubber, which has the problems of heat generation, shoulder cracking and so on. It can not meet the requirements of heavy load, high mobility and long-distance driving. Mechanical characteristics of inserts supporting run-flat tire is investigated in order to improve driving performance under zero pressure. Based on the tests of zero pressure load characteristics, lateral mechanical characteristics and tire grounding characteristics, the law of mechanical characteristics parameters of inserts supporting run-flat tire under different loads was studied. The mechanical characteristics parameters under zero pressure and rated tire pressure were comparatively analyzed. In addition, combined with the damage form of zero pressure driving failure, the mechanical characteristics of tire were analyzed. The results showed that the radial stiffness of the inserts supporting run-flat tire was approximately linear after the pressure loss, and the radial stiffness increased significantly after the insert takes part in the load-bearing. When there was no obvious sideslip, the lateral stiffness increases and the lateral adhesion decreases. When the load reached a certain value, the area of the tire's grounding footprint basically remained unchanged. In the center of shoulder and crown of tire, stress concentration appeared. At this time, the tread warpage was serious, and the uniformity of the ground pressure distribution was poor. When the load was less than 6 000 N, the tire mainly depended on the structural load of the sidewall, and its radial stiffness was 84.76% lower than that under the rated tire pressure condition. When the load was more than 6 000 N, the tire mainly depended on the insert, and the radial stiffness of the tire increased significantly, which was 283.34% higher than that under the rated tire pressure condition. The lateral stiffness characteristic curve consisted of the zone without obvious side slip, transition zone and obvious slip zone under zero pressure. In the region without obvious side slip, the relationship between lateral force and lateral displacement was approximately linear, while in the region of transition and obvious side slip, it was nonlinear. The average lateral stiffness of the tire without obvious sideslip area was 9.92% higher than that of the tire with rated tire pressure. The warpage of tire tread and the variation of uniformity of ground pressure distribution were more significant than those under rated tire pressure condition. When the load increases to 9 800 N, the length, width and area of the grounding footprint remained unchanged. The shoulder on both sides and the crown corresponding to the contact of the insert became the main bearing area of the tire.