The present invention is a system which improves the installation and provides a seal between tubeless tires and the rims of the wheels upon which they are mounted. A pliant sealing member or ring (10) is placed over the base (21) or rim of the wheel The ring has an opening to match the valve opening (27) of the rim. A special valve stem sleeve (15) may be provided to enhance the sealing of the valve stem. The invention features a stretch zone (19) which allows universal fit for a range of wheel sizes and also accommodates the drop center (24) of wheels. A method of casting the ring (10) is disclosed which includes the design of a mold (40) and the production of twin rings which are cut when completed to form two separate rings (10). The sealing ring (10) may be made of vinyl having a durometer rating of between 50-75 and a thickness of 0.5-1.0 mm.