Tires

Tire - New and Used Tires and Repair

Tire
A covering mounted on the rim of a wheel that serves as a cushion and surface for traction. Tires are used on road vehicles, tractors, aircraft and spacecraft landing gear, factory and warehouse machinery, and on a variety of other vehicles, including shopping carts and baby carriages. Tires are made of chemically treated rubber and fabric. Those for indoor use are generally solid rubber with a smooth surface, while those used outdoors are pneumatic, or hollow and filled with pressurized air, and have a traction pattern cut into the surface. This article deals primarily with pneumatic tires.
The main parts of the pneumatic tire are the tread, the body, and the beads. The tread is a thick pad of rubber into which grooves are cut to form cleats or ridges. The tread provides traction to move and stop a vehicle and to prevent skidding and sliding while a vehicle is in motion. Tractor and snow tires have especially deep grooves that enable the tire to move through soft earth or deep snow.
The body gives the tire its strength and form. It consists of layers of fabric permeated with rubber. The fabric in most passenger-vehicle tire bodies is polyester. Each fabric layer is called a ply, and the strength of a tire is sometimes described by the number of plies in its body. Most automobile tires have two plies.
The beads of a tire are the two bands that hold the tire to its wheel. They are located along the tire's inner edges and are made up of strands of wire surrounded by rubber and covered with fabric.
Pneumatic tires are made in a variety of sizes. The size is usually indicated by a code such as P205/75R14. The letter P identifies the tire as a passenger-car tire. The number 205 is the width of the tire measured in millimeters. The number 75 is the tire's height-to-width, or aspect, ratio. This tire has sidewalls that are 75 percent as high as the tire is wide. The letter R stands for radial, which is a design type, and 14 means that the tire will fit a rim 14 in (36 cm) in diameter. A P205/75R14 tire would be used on a medium-sized car. A large car might use a P225/75R15 tire, and a compact car might use a P155/80R13 tire.
Tires are made of both natural and synthetic rubber; chemicals, such as carbon black, oils, and waxes, which are added to strengthen the rubber; and fabric, which may be nylon, polyester, or steel fabric. Each part of a tire requires its own mix of chemicals and rubber.
When a tire is manufactured, raw rubber and chemicals are blended in large mixers with two steel-toothed paddle wheels that turn against each other. The rubber is heated and kneaded to a gummy consistency. The mixture is then removed from the mixers and fed through a pelletizer, which extrudes small rubber pellets.
Meanwhile, fabric is dipped in latex and subjected to a stabilization treatment. The rubber pellets are again kneaded to a hot, gummy texture. Then the rubber is molded into a thin coating, which is pressed into each side of the fabric. The coated fabric is cut into lengths to make one layer, or ply, of the inner body of the tire.
Rubber is also applied to high-tensile bronze-coated steel wire. Several strands of the rubber-coated wire are wound into a hoop and then sewn with nylon cord to form each of the two tire beads. Another batch of rubber is fed into an extruder, which forces soft rubber through a die or opening to create a covering that has the basic shape of the tread and sidewall.
The fabric, beads, and covering are combined on a tire-building machine. A tire builder applies layers of fabric to a revolving drum to form the inner core of the tire. The builder then places a wire bead around each end of the drum, turns the fabric up to cover the beads, and finally wraps the rubber covering around the other parts.
The tire parts are then fused together in a tire press, which contains an aluminum mold with the outline of the tread design and sidewall lettering. As the press closes on the tire, a rubber bladder inflates and forces the tire, whose outside is still soft rubber, into the mold. After curing, the tire is automatically ejected onto a conveyor belt to be inspected, balanced, and trimmed.
In conventional bias-ply construction, the threads, or cords, of the fabric ply lie at an angle to the tread line of the tire. In radial tires, the cords run straight across. Radial tires also have fiberglass or steel belts between the plies and the tread. A bias-belted tire combines these features and has both angled cords and a belt. This arrangement strengthens the sidewalls and increases the tire's load-carrying capacity.
Wheel rims were traditionally protected by metal bands. The use of rubber wheels was not feasible until 1839, when American inventor Charles Goodyear discovered the process of vulcanization, which made rubber stronger, more elastic, and less sticky. In 1845 the first pneumatic tire was patented by Scottish inventor Robert W. Thomson. Hundreds of different tire designs using leather, rubber, and other materials were soon patented. The tire industry did not flourish, however, until pneumatic rubber tires were refined and patented in 1888 by British inventor John Boyd Dunlop.
In 1895 the Hartford Rubber Works made the first pneumatic tires in the United States. This company later became part of the United States Rubber Company, now called Uniroyal. Leading tire manufacturing firms produce about 300 million tires per year worldwide for trucks, buses, and automobiles. Many of the manufacturers are based in Akron, Ohio.