The ornamental design for a tread portion of an automobile tire, as shown and described.
FIG. 1 is a perspective view of the tread portion of an automobile tire showing my new design, it being understood that the pattern repeats uniformly throughout the circumference of the tread;
FIG. 2 is a front view thereof;
FIG. 3 is a top view thereof;
FIG. 4 is a right side view thereof; the opposite side being identical thereto;
FIG. 5 is a fragmentary enlarged front view showing the details of the tread portion thereof;
FIG. 6 is a section view taken along line 6-6 in FIG. 5; and,
FIG. 7 is a section view taken along line 7-7 in FIG. 5.
Broken lines are used to show portions of the tire that are not being claimed, and thus form no part of the claimed invention.