AUTOMOTIVE
What’s Inside a Tire?
A look at the structure of a modern car tire and how its makeup is tailored to its purpose.
By Graham Heeps | Illustration by Guilherme Henrique
Most modern automobile tires are black rubber and donut-shaped (the technical term is a “toroid”). But like any consumer product, a car tire is the sum of its parts. And depending on the purpose and price of the tire — and on the technology available to the company making it — those components can vary considerably in each product. Let’s take a closer look at what’s inside.
Bead At the tire’s innermost edge, rubber-wrapped bead wire reinforces the structure, enabling the tire to keep its shape and stay securely on the rim as it rolls.
Carcass
Think of this as the skeleton of the tire — it carries the weight. The carcass consists of multiple layers or plies of nylon or rayon cords, arranged radially across the tire from bead to bead — hence “radial tire." Around this, reinforcing materials and rubber compounds are moulded. Sidewall
Different rubber compounds and reinforcing materials are used strategically in a tire for specific performance objectives. In the sidewall — literally the side of the tire, between the bead and the tread — flexibility and durability are the priorities, so robust natural rubber is commonly used. During manufacturing, all the uncured or “green” rubber compounds in the tire are moulded in a heated press to create their final form and properties. Markings engraved in the mould are transferred to the sidewall during curing, which is when heat and pressure are applied to the tire in the mould. This process creates the tread pattern and sidewall marking (which indicates where and when the tire was made, as well as its manufacturer, model and size).
“The size and distribution of the tread pattern elements control highway noise; this is especially noticeable in EVs.”
Belt
This unsung hero, hidden under the tread, reinforces and stabilizes the tire. The belt package typically contains two or more diagonally arranged steel-cord layers.
Tread
The tire’s most distinctive element is formed from a mix of synthetic and natural rubbers, along with reinforcing fillers like silica or carbon black, and other ingredients. The tread formulation (and even how the ingredients are mixed) works in conjunction with the tread pattern to dictate how the tire grips and wears. For example, the size and distribution of the tread pattern elements control highway noise; this is especially noticeable in EVs. Meanwhile, winter treads have many more sipes (small, wavy slits) and are made of a more pliable compound than all-season tires. These small variables allow each type of tire to perform as required, so it’s a good idea to talk to your mechanic about the kind of driving you do most. AMA
Bead At the tire’s innermost edge, rubber-wrapped bead wire reinforces the structure, enabling the tire to keep its shape and stay securely on the rim as it rolls.
Carcass
Think of this as the skeleton of the tire — it carries the weight. The carcass consists of multiple layers or plies of nylon or rayon cords, arranged radially across the tire, from bead to bead (hence “radial tire.”) Around this, reinforcing materials and rubber compounds are moulded.
Sidewall
Different rubber compounds and reinforcing materials are used strategically in a tire for specific performance objectives. In the sidewall — literally the side of the tire, between the bead and the tread — flexibility and durability are the priorities, so robust natural rubber is commonly used. During manufacturing, all the uncured or “green” rubber compounds in the tire are moulded in a heated press to create their final form and properties. Markings engraved in the mould are transferred to the sidewall during curing, which is when heat and pressure are applied to the tire in the mould. This process creates the tread pattern and sidewall marking (which indicates where and when the tire was made, as well as its manufacturer, model and size).
Belt
This unsung hero, hidden under the tread, reinforces and stabilizes the tire. The belt package typically contains two or more diagonally arranged steel-cord layers.
Tread
The tire’s most distinctive element is formed from a mix of synthetic and natural rubbers, along with reinforcing fillers like silica or carbon black, and other ingredients. The tread formulation (and even how the ingredients are mixed) works in conjunction with the tread pattern to dictate how the tire grips and wears. For example, the size and distribution of the tread pattern elements control highway noise; this is especially noticeable in EVs. Meanwhile, winter tread have man more sipes (small, wavy slits) and are made of a more pliable compound than all-season tires. These small variables allow each type of tire to perform as required, so it’s a good idea to talk to your mechanic about the kind of driving you do most. AMA