Rubber is naturally white, so why are car tires black? According to Bridgestone, a Japanese manufacturing company, this wasn’t always the case. Car tyres used to be white but the addition of carbon black has become routine because it improves durability.
Carbon black is almost (97 percent) pure carbon. It is created during a process of incomplete combustion, which is when there is not enough oxygen present to produce the normal products of combustion (water and carbon dioxide), of petroleum products under controlled conditions. It looks like small black pellets or fine black powder, and can be added to rubber, plastic and printing ink as well as tires. According to the International Carbon Black Association, some 18 billion pounds (8.1 million metric tons) of the stuff is produced each year.
By adding carbon black, manufacturers can make tires more resistant to heat and abrasion, and more tough overall. The material is also able to protect the tire from UV light and ozone, which can cause additional deterioration. In short, carbon black boosts the lifespan of the tire. According to Goodyear Motors, tires that do not contain carbon black are unlikely to last 5,000 miles (8,000 kilometers) and this would require most drivers to replace their tires once or twice a year.
The inclusion of carbon black also makes the rubber compounds found in tires more electrically conductive. This offers an escape path for the static charge that could otherwise build up and could cause an electric shock. Another, more aesthetic benefit to adding carbon black is that it can make it easier to keep your tires clean – or, perhaps more accurately, hide discoloration and dirt they might pick up on the road.
Just as tires were not always black, they were not always made out of rubber. According to the magazine Road & Track, early tires were made of wood and warped in a strip of iron. But while these early tires may have been sufficient for the horse drawn carts of the nineteenth century, twentieth-century motors required something sturdier. While some early examples – such as Robert Thomson’s rubber tube wrapped in leather – did not last the long haul, John Boyd Dunlop’s pneumatic tire was patented in 1888 and has become the standard still in use today.
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