The research into vibration characteristics of a loaded and rolling tire is essential for the prediction of spindle forces. There are tire vibration characteristics one of which is the first natural frequency of a loaded and rolling tire is lower than that of an unrolling tire. The vibration characteristics, for a loaded and rolling tire, are affected by the effect of rotation, restrictions of the vibration due to road contact, and the behavior of rubber dependent on amplitude strain. The consideration of the degradation of natural frequency is therefore necessary in the tire model for prediction of spindle forces.This paper describes an identification method for the tire equivalent stiffness of a tire model focused on vertical spindle forces. The first mode is dominant in vertical spindle forces.First, the natural frequencies in rolling and unrolling tires are identified by operational impact test. Second, the tire vibration model, based on the cylindrical shell theory, is built up. The basic equation, including the effect of rotation, is derived from the thin rotating cylindrical shell model. Consequently, it is found that the effect of rotation and restrictions of the vibration have no effect on the first mode. The results present vibration characteristics of a rolling tire estimate based on an unrolling tire.