The ornamental design for a sidewall of a tire, as shown and described.
FIG. 1 is a right side perspective view of a sidewall of a tire showing our new design;
FIG. 2 is a right side elevation view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a rear view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The portion of the sidewall between the broken lines of uneven length includes the claimed design. The broken lines of even length depict environment and element depicted in broken lines of even length form no part of the claimed design. The rear of the sidewall is not seen during ordinary use and is no part of the claimed design. The sidewall opposite the one depicted, and the tread surface form no part of the claimed design.