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