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 our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a right side view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a rear view thereof;
FIG. 6 is a fragmentary enlarged front view surrounded by line 6-6 in FIG. 2; and,
FIG. 7 is a sectional view taken along line 7-7 in FIG. 6.
In the drawings, the broken lines defining portions of the tread, 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.