The ornamental design for a diskwheelcover, as shown and described.
FIG. 1 is a perspective view of a disk wheel cover showing my new design;
FIG. 2 is a front elevational view thereof; and,
FIG. 3 is a partial (elemental) enlarged view thereof.
The broken line showing of the rear portion of the disk wheel cover in FIG. 1 is included for the purpose of illustrating environment and forms no part of the claimed design. The dash dot line on either side of the spoke segment of the disk wheel cover in FIG. 3 is for the purpose of illustrating the boundary of the claimed design and forms no part thereof.