The metal part of a tire that holds the tire in place is called the rim. The rim is the outer edge of the wheel and is typically U-shaped, with the center being deeper than around the edges. It is designed to support the bead of the tire and is made of the same metal or alloy as the rest of the wheel, with the addition of a Teflon covering for increased protection. The rims primary role is to support and seal the tire to the wheel, maintaining the air inside the tubeless tire by ensuring an appropriate fit. The entire metal portion that holds the tire is the wheel, which connects to the hub of an automobile through an axle.