A pneumatic tire and vehicle wheel assembly, the wheel being of the split-rim type without a tire mounting well in the base portion of the rim. A support member is provided extending radially fr0m the base portion of the rim to contact and support the tread region of the tire when the tire is wholly or partially deflated. The support member is preferably of L-section so as to have a cantilever flange to contact the tire and is preferably heat-conductive. A lubricant is preferably included in the tire cavity which will be between the tire and support member when the former contacts the latter. The support member is preferably adjacent one of the bead seats of the rim to serve the secondary purpose of retaining the tire bead on said seat. The support member may be an integral, radially outer part of the wheel disc or a separate, annular component surrounding the base portion of the rim.