An auxiliary wheel is to be paired with a main wheel of a vehicle, while the main wheel remains on the vehicle. The auxiliary wheel includes a disk having a wheel rim, as well as a tire mounted on the wheel rim. In order to securely mount the auxiliary wheel on the main wheel, a bolt is insertable through a hole in the disk of the auxiliary wheel, the hole being eccentric with respect to the rotational center of the auxiliary wheel. An arcuate guide slot is formed in the auxiliary wheel disk, the guide slot forming an arc of a circle centered on the hole. A threaded rod fits into the slot and can be threaded into the main wheel, and tightened when the centers of the main and auxiliary wheels become concentric after mounting.