Tires are made of layers of rubber, polyester and steel. Plies, which hold a tire's structure, are typically made of polyester cords encased in rubber. Belts made of steel wires wrap around the tire's core. The braided-steel bead and chaffer portion sits against the wheel.
The sidewall is a layer of thick rubber, and the rubber tread area constitutes the visible portion of the tire. Grooves and sipes, the small breaks in the tread, split the tread into separate blocks to remove water efficiently. The rubber shoulder is the rounded area where the tire's tread joins its sidewall. Once tires are constructed, they are inserted into a heated pressing machine, which creates the tread and melts the tire layers together. The process allows tires to return to their original shape after flexing.