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 according to my new design;
FIG. 2 is a front view thereof;
FIG. 3 is a top view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a rear view thereof;
FIG. 7 is a fragmentary enlarged front view showing the details of the tread portion thereof;
FIG. 8 is a section view taken along line 8-8 in FIG. 7; and,
FIG. 9 is a section view taken along line 9-9 in FIG. 7.
Broken lines in the drawing figures are used to show portions of the tire that are not claimed, and thus form no part of the claimed invention. The dot dash line shows a border between claimed and unclaimed subject matter.