Tire Components: What Makes Up A Tire

The automotive tire is an assembly of numerous components that are built up on a drum and then cured in a press under heat and pressure. Typical components used in tire assembly are listed below:

Inner Liner

The inner liner is an extruded rubber sheet compounded with additives that result in low air permeability. The inner liner assures that the tire will hold high-pressure air inside, without the air gradually diffusing through the rubber structure.

Body Ply

The inner liner is an extruded rubber sheet compounded with additives that result in low air permeability. The inner liner assures that the tire will hold high-pressure air inside, without the air gradually diffusing through the rubber structure.

Sidewall

Sidewalls are non-reinforced extruded profiles with additives to give the sides of the tire good abrasion resistance and environmental resistance. Additives used in sidewall compounds include antioxidants and antiozonants. Sidewall extrusions are nonsymmetrical and provide a thick rubber area to enable molding of raised letters and sidewall ornamentation.

Beads

Beads are bands of high tensile-strength steel wire encased in a rubber compound. Bead wire is coated with special alloys of bronze or brass. Coatings protect the steel from corrosion. Copper in the alloy and sulfur in the rubber cross-link to produce copper sulfide, which improves bonding of the bead to the rubber. Beads are inflexible and inelastic, and provide the mechanical strength to fit the tire to the wheel. Bead rubber includes additives to maximize strength and toughness.

Apex

The apex is a triangular extruded profile that mates against the bead. The apex provides a cushion between the rigid bead and the flexible inner liner and body ply assembly. Alternatively called "filler".

Belt Package

Belts are calendered sheets consisting of a layer of rubber, a layer of closely spaced steel cords, and a second layer of rubber. The steel cords are oriented radially in radial tire construction, and at opposing angles in bias tire construction. Belts give the tire strength and dent resistance while allowing it to remain flexible. Passenger tires are usually made with two or three belts.

Tread

The tread is a thick extruded profile that surrounds the tire carcass. Tread compounds include additives to impart wear resistance and traction in addition to environmental resistance. Tread compound development is an exercise in compromise, as hard compounds have long wear characteristics but poor traction whereas soft compounds have good traction but poor wear characteristics.

Cushion Gum

Many higher-performing tires include an extruded component between the belt package and the tread to isolate the tread from mechanical wear from the steel belts.

Various other components

Tire construction methods vary somewhat in the number and type of components, as well as the compound formulations for each component, according to the tire use and price point. Tire makers continuously introduce new materials and construction methods in order to achieve higher performance at lower cost.