1. A tire design method comprising the steps of: (a) deciding an initial layout of one pitch unit of a tire tread pattern; (b) creating a finite element model of a tire by developing the one pitch unit of the initial layout into a plurality of pitches in the circumferential direction of the tire; (c) calculating an evaluation index for each element through a structural analysis using the finite element model of the initial layout; (d) integrating calculated evaluation indices into one pitch unit for each element associated with the indices, classifying the elements according to the magnitudes of the integrated evaluation indices to determine a plurality of classes to which elements subject to removal belong, and selecting elements to be removed from each of classes thus determined; (e) selecting elements to be added from among the elements which have been removed; (f) obtaining a layout of the current generation through the removal and addition of elements at the steps (d) and (e) to create a finite element model of a tire by developing one pitch unit of the layout into a plurality of pitches in the circumferential direction of the tire; (g) calculating an evaluation index for each element through a structural analysis using the finite element model of the layout of the current generation; and (h) determining convergence of an objective function from the calculated evaluation indices, updating the layout to the layout of the current generation and returning to the step (d) when it is determined that convergence has not occurred, and deciding a tire tread pattern using the layout of the current generation as an optimum when it is determined that convergence has occurred.