Rubber index calculating method of a tire, apparatus, and program

To precisely calculate the rubber index of a tire. A rubber index calculating device (12) measures, by a frictional energy measuring device (14), frictional energies of a tire in plural tire input conditions applied to the tire on the basis of the shear force and the slippage of a tire contact patch, measures, by the frictional energy measuring device (14), frictional energies of a sample of the same material as the tire in sample input conditions that have been set on the basis of the frictional energies of the tire in the tire input conditions that were measured, and sets a measurement conditions for measuring amounts of wear of the sample on the basis of the frictional energies of the tire in the tire input conditions that were measured and the frictional energies of the sample in the tire input conditions that were measured, measures, by an amount of wear measuring device (16), the amounts of wear of the sample in the measurement conditions that were set, and calculates the rubber index of the tire on the basis of the frictional energies and the amounts of wear of the sample that were measured.