To shorten the computing time when forecasting tire performance.

In this tire performance forecasting method, tires and rims provided in wheels are divided into a plurality of fine elements to form a rim model 20 and a tire model 30. The rim model 20 and the tire model 30 are arranged so that a rim side fitting surface Sr and a bead part side fitting surface Sb face to each other and that the rim side fitting surface Sr and the bead part side fitting surface Sb are arranged with the predetermined space in the radial direction of the rim model 20 or the tire model 30. After adjusting positions of the bead part side fitting surface Sb of the tire model 30 and the rim side fitting surface Sr of the rim model 20 in the radial direction, bead parts 31 and 32 of the tire model 30 are fitted in the rim model 20.