The ornamental design for a tire tread shoulder, as shown and described.
FIG. 1 is a side perspective view of a tire tread shoulder showing our new design, it being understood that the pattern is repeated throughout the circumference of the tire, the opposite side being the same as that shown;
FIG. 2 is a side elevational view thereof, the opposite side being identical thereto;
FIG. 3 is a front elevational view and the opposite side being the same as that shown;
FIG. 4 is an enlarged fragmentary side elevational view thereof;
FIG. 5 is an enlarged fragmentary view thereof; and,
FIG. 6 is an enlarged fragmentary view thereof.
The regular dash lines are included for the purpose of illustrating portions of the tire tread shoulder that form no part of the claimed design. The bold dot-dash-dot lines represent boundaries of the claimed design.