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 front view showing the details of the 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 defining the sidewall, inner bead and the peripheral boundary between the tire tread and sidewall are for the purpose of illustrating environment and form no part of the claimed design.