The ornamental design for a spare tirecover, as shown and described.
FIG. 1 is a front elevation view of a spare tire cover
FIG. 2 is a left side perspective view of a spare tire cover
FIG. 3 is a right side perspective view of a spare tire cover
FIG. 4 is a top plan view of a spare tire cover
FIG. 5 is a bottom plan view of a spare tire cover; and,
FIG. 6 is a rear plan view of a spare tire cover.
The broken lines showing of the tire wheel rim is included for the purpose of illustrating environmental subject matter and forms no part of the claimed design.