A wheel (10) comprising means for providing one or more protrusions in a ground-engaging surface of the wheel. In some embodiments, the wheel comprises a first hub (18), a tire (12) mounted on the first hub (18), a second hub (20) rotatable with respect to the first hub (18), and means for deforming the tire in a generally radial direction in response to relative rotation between the first (18) and second hubs (20). The invention also provides a wheel cover (110) comprising an outer surface having one or more protrusions and, when the cover is fitted to a wheel, the outer surface of the cover (110) provides the ground-engaging surface (114) of the wheel. The wheel (10) and wheel cover (110) of the invention are particularly suited for use with prams and similar vehicles in order to impart a rocking motion to the pram during use.