A variable outer diameter wheel includes a generally cylindrical pipe or drum having four equally spaced penetrating holes or receiving parts in the cylindrical wall, a diaphragm sealing member corresponding to each of the penetrating holes and fitted to the pipe support, and sliders forming a wheel peripheral face so that the sliders can smoothly slide in the penetrating holes. The sliders are pushed or activated and moved outward from the pipe in a direction so the wheel outer diameter is enlarged by compressed air supplied through a passage and a hole provided in an axle which support the wheel. Exhausting the compressed air causes the wheel outer diameter to decrease and restores the wheel to its original size. Variable outer diameter wheels permit safe operation of vehicles on frozen, snow-clad or irregular surfaced roads.