The ornamental design for a single-wheeled motor vehicle with auxiliary wheel, as shown and described.
FIG. 1 is a front view of a single-wheeled motor vehicle with auxiliary wheel;
FIG. 2 is a rear view thereof;
FIG. 3 is a top plan view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a front perspective view thereof as seen from the right side thereof; and,
FIG. 6 is a rear perspective view thereof as seen from a left side thereof.
The broken lines in the drawings illustrate portions of the single-wheeled motor vehicle with auxiliary wheel that forms no part of the claimed design.