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 according to my design;
FIG. 2 is another perspective view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a plane view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a left side view thereof;
FIG. 7 is a rear view thereof; and,
FIG. 8 is a fragmentary enlarged view showing the details of the tread portion thereof.
In the drawings the broken lines defining the sidewall, inner bead 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.