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 fragmentary enlarged view showing the details of 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.
The broken lines showing portions of the tire tread, the inner bead, sidewall, and peripheral boundary between the claimed tread and the sidewall are for the purpose of illustrating environment and form no part of the claim.