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;
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 view showing the details of the tread portion thereof;
FIG. 8 is an end view taken along the line 7-7 in FIG. 7; and,
FIG. 9 is an end view taken along the line 8-8 in FIG. 7.
In the drawing figures, the broken lines defining the sidewall, inner bead and the peripheral boundary between the claimed tire tread and the sidewall depict environmental subject matter that forms no part of the claimed design.