Methods of forming a tire 4 directly on a wheel in which the wheel has a conduit which runs between its hub and rim. A mold is placed over the wheel in order to form a cavity between an inner surface of the mold and the wheel's rim. Liquid materials to form the tire 4 are injected into the cavity via the conduit and the wheel spun to distribute the materials throughout the cavity, which materials solidify to form the tire 4 attached to the wheel. The method includes the step of placing a hub cap 6 over a face of the wheel prior to placing the mold and sealing the hub cap 6 to the wheel during the molding process. The tire 4 may have a substantially hollow interior 50 which may include a flexible web 18 sealed within the rim of the wheel by the hub cap 6.