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 fragmentary enlarged front view showing the details of the tread portion thereof; and,
FIG. 8 is section view taken along line 8-8 in FIG. 7.
In the drawings, the broken lines defining the sidewall, inner bead and the part of the shoulder tread groove that intrudes into the sidewall depict environmental subject matter that forms no part of the claimed design.