The radial tire was tested by the tire comprehensive testing machine to analyze the stiffness characteristics and grounding characteristics of the tire under different tire pressure and vertical load. The results show that the stiffness of different directions changes when the tire pressure increases. The longitudinal stiffness increases slightly and the torsional stiffness increases when the vertical load increases. As the vertical load increases, the tread impression changes from the ellipse to the approximately rectangle, and the area of the tread impression is slightly increased. As the tire pressure increases, the area of the tread impression is significantly reduced.