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What Are Tires Made Of? (Tire Structure)

What Are Tires Made Of? (Tire Structure)

Dec 29th 2020

According to common consensus, the first true automobile was created in 1885 by Carl Benz, known as the Benz “three-wheeler” to be precise. Although this claim is disputed, as there were other types of automobiles with various methods of motion and styles. Along with the boom of the automobile, the tire industry has also since become one of the most profitable branches of industry. The global automotive tire market was valued at $112.16 billion in 2019, and is projected to reach $154.40 billion by 2027.

Origins

The first synthetic rubbers were invented in the laboratories of Bayer in the 1920s. In 1946, Michelin developed the radial tire method of construction. Michelin had bought the bankrupt Citroën automobile company in 1934, so it was able to fit this new technology immediately. Because of its superiority in handling and fuel economy, use of this technology quickly spread throughout Europe and Asia. In the US, the outdated bias-ply tire construction persisted, until the Ford Motor Company adopted radial tires in the early 1970s, following a 1968 article in an influential American magazine, Consumer Reports, highlighting the superiority of radial construction.

Manufacturing Materials

Many kinds of rubber are used, the most common being styrene-butadiene copolymer. Tire factories start with bulk raw materials such as synthetic rubber, carbon black, and chemicals to produce numerous specialized components that are assembled and cured. Modern tires are made of approximately 20% natural rubber and 25% synthetic rubber, which is a plastic polymer. The rest is made up of metal and other compounds. There are four types of rubber used in the manufacture of tires:

  • Natural rubber
  • Polybutadiene rubber
  • Butyl rubber
  • Styrene-butadiene rubber

Most tire manufacturers today use carbon black or silica, or a combination of both as reinforcing fillers when formulating tire compounds. These ingredients lower the tire’s rolling resistance, reinforce the tire’s grip on the road and even serve as protection from damage.

Fillers

The majority of tire manufacturers today use either carbon black or silica (or a combination thereof) as reinforcing fillers when formulating rubber compounds. They’re useful because they enhance tire grip, resist punctures and give tires lower rolling resistance. Carbon black and silica are also available in different forms, and each one influences a tire’s handling characteristics in different ways. This is handy for researchers who are constantly looking for the right combination to achieve optimal performance for different driving styles, vehicle types and road conditions.

The downside to carbon black and silica is that they’re expensive to produce. As a result, researchers are now experimenting with cellulose fibers, oils and other plant materials as alternative fillers that provide value without sacrificing performance.

  • Cornstarch
  • Dandelions
  • Walnut shells
  • Wood pulp

Over 200 ingredients go into a tire. They play vital roles in safety, fuel efficiency, performance and eco-friendliness. These components fall into five groups:

Natural rubber: the main component of the tread layers

Synthetic rubber: part of the treads of car, van and 4x4 tires

Carbon black and silica: used as a reinforcing agent to improve durability

Metallic and textile reinforcement cables: the "skeleton" of the tire, forming the geometric shape and providing rigidity.

Numerous chemical agents: for unique properties like low rolling resistance or ultra-high grip

Natural rubber is harvested mainly in the form of the latex from the rubber tree. The latex is a sticky, milky colloid drawn off by making incisions in the bark and collecting the fluid in vessels in a process called "tapping". The latex then is refined into rubber that is ready for commercial processing. In major areas, latex is allowed to coagulate in the collection cup. The coagulated lumps are collected and processed into dry forms for sale.

Synthetic rubber is manufactured by utilizing polymers extracted from crude oil. As the technology of rubber manufacture has progressed, more natural materials are being utilized, for example the use of plant oils has become more frequent, as a bid on part of the manufacturers to lower their negative environmental impact, create a more sustainable production model and increase performance of their product. Synthetic rubber offers a different range of physical and chemical properties. Synthetic rubbers are superior to natural rubbers in two major respects: thermal stability and resistance to oils and related compounds. They are more resistant to oxidizing agents for example, such as oxygen and ozone which can have a negative impact on a tire.

Carbon black is a material produced by the incomplete combustion of heavy petroleum products such as FCC tar, coal tar, or ethylene cracking tar. It is mainly used as a reinforcing filler in tires and other rubber products.

Silica is a filler used with or instead of Carbon Black in tread and sidewall compounds. It is widely used in premium tires.

Reinforcement cables: These textiles are polyester cord fabrics, rayon cord fabric, nylon cord fabric, and aramid cord fabric. They are used to make the tire plies in passenger tires. While they serve as the primary reinforcing material in the tire casing and they also help the tire keep its shape in different road conditions which provide added endurance and performance characteristics to the tire.

Tire Construction

A tire consists of bead, bead filler, belts, body ply, inner liner, sidewall and tread.

Bead: Tire bead bundles (usually strands of wire) secure the tire to the wheel. It is the part of the tire that contacts the rim on the wheel. The bead is typically reinforced with steel wire and compounded with high strength, low flexibility rubber.

Bead Filler: is a rubber compound placed above the bead bundle that may be used between the body plies which wrap around the bead to tune ride and handling characteristics.

Belts: Typically, two belts with steel cords laid at opposing angles. Belts provide stability to the tread area of the tire, which contributes to wear, handling and traction.

Body Ply: Most tires have one or two body plies, each typically composed of polyester, rayon, or nylon cords within a rubber layer. Body plies function as the structure of the tire and provide the strength to contain the inflation pressure.

Inner tube liner: is a rubber compound used to retain the inflation pressure inside the tire.

Sidewall: is the part of the tire that bridges between the tread and bead. It is a rubber compound that is reinforced with fabric or steel cords that provide tensile strength and flexibility used to cover the body plies on the sides of the tire, which provides abrasion, scuff and weathering resistance.

Tread: is a thick rubber, or rubber/composite compound formulated to provide an appropriate level of traction that does not wear away easily. The tread rubber compound and tread pattern provides contact with the road and abrasion resistance contributing to traction and treadwear.

Protective Elements

A wide range of additives are used in tire manufacture, in both internal and external components to protect the tire from degradation. These are largely comprised of:

  • Antioxidants: help to keep rubber from the breaking down due to the effect of temperature and oxygen exposure.
  • Antiozonants: are used to impede the effects of exposure to ozone on the surface of the tire
  • Anti-aging agents: various chemicals used to prolong the tire’s service life.

These compounds prolong the life of a tire and help prevent sidewall cracking caused by UV radiation and the presence of ozone. These additives also improve tread wear.