The ornamental design for a sidewallportion of an automobile tire, as shown and described.
FIG. 1 is a perspective of a sidewall portion of an automobile tire;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a top plan view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a fragmentary enlarged view showing the details of the sidewall portion defined by cross-section by lines A-A, B-B, C-C and D-D in FIG. 2 thereof; and,
FIG. 7 is an end view taken along line E-E in FIG. 6 thereof.
The broken line showing of the tire is included for the purpose of illustrating environment and forms no part of the claimed design.