Parts of a Tire: A Complete Guide

Parts of a Tire

There are a lot of different parts that compose a tire. A tire has beads, bead filler, cord body, liner, plies, tread, sidewall, and more.

Casing

The casing, also referred to as the carcass, is the interior of the tire. The casing will provide a cushion and contains the air that allows the tire to function correctly. It works in a simliar manner as a traditional inner tube. The casing does not refer to the air that it contains, only the parts of the tire.

Beads

Tire beads hold the tire to the wheel’s rim which is the outer part of the wheel’s edge. The beads will be made of steel wires woven into a rubber band. These wires are coated with another metal like bronze or copper. The tire beads are there to prevent the tire from sliding out of place while it is in motion.

Bead Filler

The bead filler is a compound with the consistency of rubber that is inside of the beads. The purpose of the bead filler is to give stability to the sidewall and the area at and around the tire beads. The bead filler is stiff and dense and will help the performance of the tires.

Bead Reinforcement

The bead reinforcement is made of a synthetic fiber that creates a cabling. Usually, the bead reinforcement will be composed of nylon or aramid. The bead reinforcement will enhance the directional stability of the tire. It will also help with handling and steering response.

Bead Apex

The bead apex is a wedge of synthetic rubber that offers a stabilization component to the beads of the tire. The bead apex works towards the same ends that the bead reinforcement does. However, the bead apex will also give the driver more comfort when steering the vehicle.

Bead Core

The bead core is made out of steel wire that is embedded in rubber. The core will make sure that the tire will hold firm to the rim of the wheel.

Radial Cord Body

The radial cord body will provide strength to the tire. It will also transfer forces that impact the tread to the wheel. Body plies make up the cord body and consist of fabric cords coated in rubber. The body plies can be made of different fabrics including polyester, rayon, and nylon.

Bias ply tires, often also referred to as cross-ply tires, are tires that contain cords that run diagonally between the beads. The cords will have an angle of somewhere between 30 and 40 degrees. Each additional ply will be at a different angle in order to create a crossing pattern underneath the tread. These tires offer a smooth ride, even on rough or uneven driving surfaces. However, they do not have as much traction or control available at higher speeds and have more drag or rolling resistance than other tire constructions.

Belted bias tires are similar to bias ply tires. The difference is that belted bias tires have the addition of steel or fiberglass belts. These will help to increase the stiffness of the tread and reduce the rolling resistance.

Radial tires are made up of parallel cords that are perpendicular to the centerline of the tread. These cords will also have stabilizer belts made of steel wire or other strong cord materials. These are placed on top of the perpendicular cords. Radial tires have reduced rolling resistance and great handling. They also tend to have a long tread life. They are not as good for rough driving surfaces if you are driving slowly. A ride with radial tires is generally more rough as well.

Inner Liner

The inner liner is a compound that is bonded to the cord body. Even under pressure, this rubber compound will hold air and works in a similar way as an inner tube. Most modern tires do not have inner tubes. The inner liner works with the beads and the bead filler to hold air inside the walls of the tire.

Belt Plies

The belt plies are the layers of cord that are underneath the treading. The belt plies will provide strength to the tire tread and also improve fuel efficiency, traction, lifespan, and durability. In addition, they will help the tire keep its shape and provide directional stability. It also reduces rolling resistance. The most commonly used material for belt plies is steel.

Sidewall

The side of the tire from the bead to the tread is called the sidewall. The sidewall protects the cord body as well. The sidewall contains imprinted information about the tire including the tire size, load index, and speed rating. The sidewall is also designed to resist damage.

Tread

The tread is the part of the tire that touches the surface of the road. The tread is made for performance and different tread designs offer different amounts of handling, traction, wear, resistance, and fuel economy.

The tread is made of a combination of synthetic and natural rubbers. Quality tread is important for safe driving. The places in between the tread ribs are called grooves. These grooves dispel excess water.

The part of the tread that is in contact with the driving surface the most is called the cap. This provides the traction and grip as well as resistance to wear and handling and directional stability. In addition, sipes are special types of treads that are located within the regular tire tread. The tire sipes will give you improved traction on imperfect road conditions.

Underneath the cap is the base. The base will reduce rolling resistance. It will also prevent excessive damage to the casing which is the internal structure of the tire. The shoulder is the outer edge of the tread. The shoulder is used as a transition from the tread cap to the tire’s sidewall.

Jointless Cap Plies

The jointless cap plies are directly underneath the tread of the tire. The cap plies will allow the tire to withstand higher speeds. They are made of a single rubber coated cord of nylon. This cord will go around the entire circumference of the tire from one end to the other and will never overlap.

Valve Stem

The valve stem is composed of three main parts: the body, the core, and the cap. In addition, newer cars also have a sensor located at the end of the valve stem that will alert the user if the tire pressure is too low. The valve core is the sealing part of the valve stem. The valve core prevents air loss from the tire. The valve core is tightened into the valve body to ensure that air does not seep through and forms a good seal.

The valve cap may also prevent air loss because it has a rubber seal inside of it. However, the main purpose of the valve cap is to prevent dirt and other debris from entering into the valve stem. If debris does get into the valve core, it could cause corrosion. Moisture can also find its way into the valve stem. If this happens and that moisture freezes, then you could wind up with a flat tire or gradual air loss.

Cars that were made in or after 2007 will come with a Tire Pressure Monitoring System or TPMS. This system will monitor the air pressure within the tire and alert the user if the pressure gets too low or even if the pressure is higher than it should be.