The ornamental design for a tread portion of an automobile tire, as shown and described.
FIG. 1 is a front view of a tread portion of an automobile tire;
FIG. 2 is a perspective view thereof;
FIG. 3 is a left side view thereof;
FIG. 4 is a fragmentary enlarged view showing the details of the tread portion thereof;
FIG. 5 is an end view taken along line 5-5 in FIG. 4; and,
FIG. 6 is an end view taken along line 6-6 in FIG. 4.
In the drawings, the broken lines defining the sidewall, inner bead, and the shoulder tread blocks on either side of the front face of the design depict environmental subject matter that forms no part of the claimed design.