Car tires are made of vulcanized rubber, a material that was first invented in 1844, though it was not used for tires until a later time. In 1937, the first synthetic rubber tire was invented by Goodrich and was made of a patented substance called Chemigum. Tire treads are made of a hard rubber called poly(styrene-butadiene-styrene) or SBS rubber. This rubber is a hard elastomer and is used for products that require durability. Polysterene is a tough, hard plastic and gives SBS its durability while Polybutadiene is a rubbery material that gives SBS its rubber-like qualities. Thus SBS, the rubber used in making car tires, has qualities of both rubber and plastic. The inner tube of the tire is made of Polyisoprene. Polyisoprene is the only rubber that is gas impermeable and will not allow air to escape. This means the tire will not go flat quickly as opposed to a balloon which loses much of its air in just a few days.
Parts of a car tire
A car tire is made up of a number of different parts. The tread of a tire is made of a mix of synthetic and natural rubber. It is the part with the markings and is usually the first part of a tire that a person sees. It is important that the tread be made of a strong, durable substance
Body plies are strong cords that run perpendicular to the tire treads and give strength to the tire. These can be made either of wire or fiberglass fabric. Usually they are made of steel. A typical car tire has two body plies as opposed to airplane tires, which have 30 or more plies.
The sidewall protects body plies and keeps air from escaping the tire.
Cap plies contain an extra layer of polyester fabric and add strength to the inner components of the tire. Not all tires have cap plies, but they play an important role in holding together tires that are used for high speeds.
A curb guard is extra rubber ribbing that runs around the sidewall of a tire. It protects the side of the tire and the wheel face from damage that may occur from hitting a curb.
A very important part of a car tire is the valve system. This is made up of an external piece of tubing that connects to the air tube inside the tire. It is used to measure air pressure inside the tire.
The bead is the base part of the tire that sits against the rim. It is made of thick steal and is coated with rubber to prevent damage to the tire from the rim and from the force used in tire mounting machines.
Formation of a tire
The various parts of a tire are assembled in a tire building machine. This machine makes sure everything is in the correct place and forms the tire into proper shape and size. After coming out of the machine, the tire has its shape, but is called a green tire as it has no markings or tread patterns. The tire is then placed in a curing machine, which vulcanizes the tire. The curing machine functions something like a waffle iron and is used to mold in markings and traction patterns. It uses heat to bond all parts of the tire together. Finally the tire undergoes a few finishing touches and is inspected.
