The ornamental design for a part of tread portion of an automobile tire, as shown and described.
FIG. 1 is a perspective view of part of tread portion of an automobile tire showing my new design, it being understood that the tread pattern repeats uniformly throughout the circumference of the tire;
FIG. 2 is a front elevational view thereof;
FIG. 3 is an enlarged fragmentary front elevational view thereof; and,
FIG. 4 is an enlarged cross-sectional view thereof taken along line 4--4 in FIG. 3.
The portion of the article shown in broken lines is for illustrative purpose only and forms no part of the claimed design.