Abstract: The present invention is primarily for providing traction for the tires of automotive vehicles in particular on snow and ice surfaces. The tire generally comprises pairs of deep and shallow channels in close proximity with each other around said tire to extend transversely from the side walls thereof toward a tread portion, said pairs being uniformly spaced at intervals around the periphery of said tire. The tire of the invention includes traction units which are always recessed in the deep channels to provide no traction, and when the traction units are disposed in the shallow channels, they provide effective traction. In addition, the invention comprises a device for converting from one type of tire to another and also a mechanism having a pneumatic bumper for protecting a supporting unit and a shifting unit from breakage when a tire is punctured.