Why Are Tires Made Of Rubber?

‍What Is the First Thing to Know about Rubber Tires?

Rubber tires are not made solely from natural rubber. Most tires that are sold on the market today come from the use of synthetic rubbers and chemical polymers. These materials have often resulted from scientific advances that have progressed throughout the past century since the advent of the automobile. While some of these discoveries have been birthed out of necessity (as in helping war efforts), the development of various compounds has steadily improved the modern tire's safety, durability, and longevity. As consumer demand expands and the pressure to find a renewable source for tire composition increases, rubber (both natural and synthetic) will play a vital role.

What Are The Compounds Found in Tires?

While rubber is a primary ingredient, over 200 chemical compounds go into the formation of tires, and several essential components of most tires are worth noting.

Natural Rubber

One of the primary components is natural rubber, harvested from plantations in Southeast Asia, Indonesia, and some parts of Latin America. The export of rubber is a significant source of revenue for the less developed countries, like Thailand, which is the leading exporter of rubber globally. These nations export over 20 billion dollars of rubber a year, and their national economies depend on it.

Natural rubber comes from a rubber tree through “tapping.” in much the same way as the syrup from a maple tree. After cutting into the bark, the rubber tree’s soft and milky substance flows from the tree into a container. These containers of pure syrup endure a refining process into the rubber that can be quickly shipped and sold on the market.

In the early days of the automobile, wooden tires were thought to be too cumbersome and inefficient. The rubber seemed to be the best substance to provide flexibility for an increased car or truckload. There were many problems, including how quickly a rubber tube would burst. In addition, rubber tended to crack and wear down when exposed to heat.

Carbon Black

Manufacturers had to find a way to ensure that tires wouldn’t pop every time the horseless carriage rolled over a tiny bump (which often happened in the early days of the automobile). By the early 1900s, scientists were experimenting with various compound substances for the budding auto industry. They discovered that combining rubber with natural substances could help strengthen rubber’s durability and lengthen its life. They searched for a cheap source of filler and found an abundant supply of charcoal to use.

Charcoal Black was discovered in 1904 by British engineers who surmised that introducing hydrocarbons from ash (primarily the charcoal from burnt wood) could provide helpful stability to rubber. These carbons (also used in black ink) were mixed with rubber and exponentially increased toughness and prevented oxidation when exposed to the sun. Using the ash as a filler increased the thickness of the tire, which also lengthened its longevity. The black pigment of the compound formed the color we know tires to be today, replacing the white pigment tires manufacturers were using. While carbon black has evolved with modern advances in chemistry, it still has a prominent role in manufacturing.

Silica

Silica is a quartz-like substance found in sand and other natural sources. In the 1990s, Michelin scientists found that adding this gritty substance to rubber could improve its flexibility and reduce the tire's resistance, aiding fuel consumption. The fact that sand was readily available made it a good choice for use, but extracting silica requires expenditures of great heat. Unfortunately, the energy used in the process does not help the environment. Currently, tire manufacturers are looking for cheaper and more viable ways of harvesting silica, including obtaining it from natural renewable sources like rice husks.

Oil/Petroleum

The advent of WWII forced the need for a durable, long-lasting tire. Rubber was in short supply due to the Axis controlling most of the world's rubber supply. Scientists needed to develop a way of synthesizing rubber from other sources to support the war effort. Their research discovered that synthetic polymers made from petroleum could work as a substitute for original rubber. While at the time, the secret formula played a role reserved for military purposes, after the war, industries began to use these polymers to mass-produce almost everything.

According to the US Tire Manufacturers Association, it takes about 7 gallons of oil to produce the synthetic rubber needed for every tire made in the US. (With an average of 2.5 billion units being made every year, that is a lot of oil). The oil binds with other chemical compounds to make the substance pliable, especially at lower temperatures. This flexibility is necessary to aid in forming the shape and tread depth of the tire. It is a relatively low-cost option that tire companies have relied on for decades.

While continued use of petroleum-based products means depleting the planet's resources, tire companies are having great success using different oils, such as soybean oil. These oils are cheaper to produce and provide an excellent source of sustainability.

Metals, Glass and Textiles

You might have noticed that tiny wires are visible from the surface when a tire loses its tread. Most tire companies use small pieces of metal wire and glass fiber to help reinforce the tire's integrity and minimize blowouts and punctures. Metal was introduced to strengthen the rim of the tire in the 1930s.

In 1967, the first PolyGlass tire was manufactured, using thin strands of latex-covered glass fibers to make up a tire’s cord. When first introduced, the two-ply tire (a layer of synthetic rubber and another made from glass fiber cord) doubled the fuel efficiency of other best-selling tires. In addition, the tire performed much better in skid control, which improved the tire's safety on wet pavements.

While it can be very upsetting to see wires protruding from the rubber, using these materials is one of the best ways to strengthen the durability and help a tire keep its shape.

Today, the search for compounds centers around finding sustainable sources of materials that are less expensive to produce while protecting the environment for future generations. The future of rubber looks bright as some of the best minds in the world work to improve the product until the day an automobile is invented that doesn’t use tires at all.