How Car Tires are Made

            Each year, over 200 million car tires are sold in the United States, accounting for $20 billion in consumer spending. The lifespan of a passenger tire has increased over time, and most are replaced after 3 to 5 years due to normal wear (“Tire and Passenger Vehicle Fuel Economy,” 1-3). As it stands, car tires are pneumatic, meaning that they hold pressurized air inside them. Car tires used to have inner tubes to form a seal with the wheel but have been designed so that the inner tube is no longer necessary (“Tire,” par. 4-8). Tire companies continue to invest in research and design in order to improve on current tire designs in order to make them less expensive, more fuel efficient, and safer. 

Materials and Production

            The main materials involved in the production of car tires are rubber—both natural and synthetic—as well as carbon black and sulfur. The materials are delivered in bulk, by railcar, to the plant where the tires are manufactured (par. 33). The first step in the tire manufacturing process is the mixing of all raw materials in order to form the tire rubber compound. The batch is repeatedly heated and pressurized to soften it and ensure an even distribution. The rubber is then squeezed into sheets. The rubber sheets are cut into specific parts of the tire. A skilled assembler pieces together the parts of the tire around a rotating metal drum. At this stage, the tire is known as a “green tire,” as it has yet to be finished. It is then cured, or enclosed in a metal mold with an inflatable bladder and then heated, in order to ensure its precise shape and capability. The tire is then tested to ensure it will operate safely and efficiently for the consumer. Any tires that do not conform to a certain standard are rejected. 

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Natural Rubber

            Natural rubber is produced by the tree Hevea brasiliensis. The tree is tapped in order to collect the latex milk it produces. This latex milk is what is shipped to the tire production companies. It later undergoes a process called vulcanization, where rubber is heated with sulfur. This gives it qualities that are more desirable for tires, such as increased elasticity, heat resistance and weather resistance (“Vulcanization,” par. 3-5).

            Before the turn of the 20th century, most natural rubber used in the United States came from rubber trees in Brazil. As cars became more prevalent, Brazil could not keep pace with the need for rubber, and prices rose. Eventually, Hevea brasiliensis seeds were smuggled out of Brazil to southeast Asia (Blaettler, par. 4-6). Currently, most of the rubber used to produce car tires comes from southeast Asia.

            Natural rubber’s production and use does not come without any ecological or social price tags. The mass growing of rubber trees has driven prices down to historically low levels, making it hard for latex producers to make a living off of their work. Like many other manufacturing industries, the natural rubber industry has been proven to utilize poor working conditions, discriminative practices, and even child labor. If not handled correctly, the chemicals involved with growing and producing natural rubber can be dangerous to humans (“About Rubber,” par. 1-5). A way to avoid these conflicts would be for tire manufactures to only buy latex milk from companies that treat their employees ethically. It does not appear that any prominent tire companies have made any statements regarding the treatment of natural rubber company employees. 

Synthetic Rubber

            The production of synthetic rubber begins with the refinement of hydrocarbons such as coal and oil. The refinement process produces the byproduct, Naphtha. Naphtha is also used to produce gasoline and plastics. Naphtha is combined with natural gas in order to produce monomers. Monomers bind molecules together in order to form more complex polymers. There are a few common types of synthetic rubber used in tire production, including nitrile rubber (NBR), butyl rubber (IIR), and styrene-butadiene rubber (SBR). Various chemicals are utilized in order to form chains of polymers. Many chains of these polymers come together to form the synthetic rubber as it is commonly known (“Synthetic Rubber Manufacturing Process,” par. 1-4). Like natural rubber, synthetic rubber also undergoes the vulcanization process. 

            Although natural rubber poses ethical problems, the production of synthetic rubber also comes with some unavoidable issues. The biggest of which is the unavoidable use of fossil fuels such as oil and coal. The use and overuse of fossil fuels has led to increased air and water pollution and has perpetuated the changing of the climate (Denchak, par. 4-7). Because current methods of tire production require synthetic rubber, the use of fossil fuels is unavoidable. There are several companies that are researching alternative ways of forming the NBR, IIR, and SBR polymers in mass quantities suitable for current tire production methods. 

Carbon Black

            Carbon black is produced by burning crude oil or natural gas with a small amount oxygen. This causes incomplete combustion, resulting in a fine soot that is necessary for tires to be made. Carbon black is required in quantities large enough that it is commonly stored in silos on the site of the tire production plant after it is shipped in by railcar (“Tire,” par. 5). Carbon black is used as a reinforcing agent in tires. Without carbon black, tires would lack the structural integrity they currently have (“Carbon Black,” par 1-3). Like synthetic rubber, the environmental problems of fossil fuel use are associated with the production of carbon black. However, there is currently no alternative to the use of carbon black. Also, like synthetic rubber, the negatives associated with the burning of fossil fuels must be accepted. There is currently no more environmentally sound way of producing carbon black. 

Sulfur

Sulfur is a naturally occurring element that is necessary for the production of car tires. It is an additive that is added to the natural and synthetic rubber at the tire production plant. It occurs naturally in the environment and is even the thirteenth most abundant element in the earth’s crust. Only around 2% of the world’s sulfur is obtained through mining. The other 98% is recovered as a byproduct of oil and gas production. In the production of tires, not a lot of sulfur is used. Sulfur is absorbed naturally by plants through their roots (“Learn More About Sulfur,” par. 1-8). The commercial production of sulfur also involves the burning of fossil fuels. Because tires do not use significant amounts of sulfur, it would be possible for the tire industry to switch to using only naturally found sulfur instead. However, sulfur is primarily used for the production of sulfuric acid. Thus, the tire industry switching away from commercial sulfur would not end the practice entirely. Most commercial sulfur used in the production of tires is made in the United States. It is then shipped by train, in a solid state, to the tire production plants to be stored before use. 

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Overview

            The production of tires is relatively ethical in nature. Although there are issues with the sourcing of natural rubber and the use of fossil fuels, most other large commercial industries employ even worse tactics. None of the materials used in the production of tires are rare or endangered. The biggest threat is if fossil fuels become scarcer or if their use is prohibited in efforts to prevent climate change. If that were to happen, the production of tires as it currently stands would not be able to continue. All of the materials needed for car tires are shipped, typically by train, to the tire production plants. From there, they are assembled by skilled workers. Many tire production plants are located in the United States. This means they are subject to United States labor laws, and employees are paid a fair wage and work under safe conditions. 

Implications 

            Like any other product, using and producing car tires has implications on the surrounding world. The main implication of buying and selling car tires is the impact it has on the environment. This is primarily due to the fact that three out of the four main raw materials involved in producing tires--synthetic rubber, carbon black, and sulfur--all require burning or otherwise using fossil fuels. However, tires are optimized for fuel efficiency. Thus, they are being designed to cut down on the amount of gasoline used to fuel America's cars. Although the use of fossil fuels is necessary for the production of tires, the total amount of fossil fuels used is being minimized.  

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