The average driver rarely thinks about tires except when it's time to buy new ones -- and then generally only in terms of what the price tag will be for replacing them. Driving enthusiasts, on the other hand, are aware of the role tires play in vehicle performance. Tires are -- almost literally -- what put the driver in touch with the road. Having a set of tires that is suitably matched to your vehicle and your driving style can make a real difference in terms of safety as well as your driving experience. Tire anatomy Tires have been around since the mid-1800s, and the earliest tires were made of solid rubber. Today nearly all tires today are radial tires -- a term that refers to the way the tire is constructed. Until recently tires were available in a variety of different constructions, including bias-ply and bias-belted. Radial tires have now pretty much replaced other varieties since their technological design offers better safety and handling, particularly at highway-driving speeds. They enable better steering and grip the road more solidly, particularly when cornering or driving on curvy roads. They also last much longer than the older styles. Although bias tires generally had a useful life expectancy of 20,000 miles or less, modern steel-belted radial tires, if properly inflated and maintained, may last for 100,000 miles or more. All modern tires have a number of elements in common. When selecting and purchasing tires, it's helpful to know a little about how they are made. The bead is a hoop of wire that runs around the inside perimeter of the tire and serves to hold the tire onto the rim of the wheel and give it extra strength (shown in cross-section, figure A). The casing is the inner body or foundation, which allows the tire to keep its proper shape when inflated. The casing (figure B) is located beneath the sidewalls and the tread and is constructed of cords. In a belted-bias tire, the cords are constructed so that they run at an angle in relation to the bead, while the cords on radial tires run straight around the tire -- perpendicular to the bead. The belts are also made of cords coated with rubber and are located beneath the tread (figure C). The materials making up the belts are another distinction between older, belted-bias tires and steel-belted radials. The earliest belts were constructed of cords made from cotton. Stronger materials such as fiberglass, nylon and polyester were later substituted for bias tires. Today nearly all tires have belts made from steel. The specific type of tire, as well as the price, is determined to a large extent by the manner in which the belts are constructed. The tread is the portion of the outer surface of the tire that actually makes contact with the road (figure D). The tread design is what provides traction and grip, allowing the vehicle to hold to the road under various driving conditions -- even under extreme conditions such as cornering at high speeds or driving on wet pavement. Since the tread is quite literally "where the rubber meets the road," it's the part of the tire that's likely to wear out soonest. Tread wear begins as soon as you start driving on a tire and is unavoidable. There are measures you can take, however, to make sure that the tread wears evenly and to help maximize the useful life of your tire. Maintaining proper tire inflation, wheel alignment and wheel balance are among the most important measures in properly caring for tires and ensuring a long tread-life. Note: A diagram of tire construction may be viewed with  Evolution of tire technology Although practically all new cars come with technologically advanced steel-belted radial tires, there are manufacturers who continue to make older-style and reproduction tires, chiefly for use on antique and classic vehicles. Taking a look at some of these reproduction tires in comparison to modern tires provides a general overview of how tires have evolved over the years. The first pneumatic tires (figure E) appeared in the 1890s. "Pneumatic" refers to the fact that the tire has a tube and is inflated with air, rather than being constructed of solid rubber. These early tires lacked the bead that modern tires use to hold onto the wheel. Instead, the inner perimeter of the rubber tire had a groove that held onto the wheel by what was known as a clincher rim. In the 1920s the tires were made so that they were slightly taller and more durable to accommodate higher speeds. It was during this period that cords were used in tire construction for the first time. The 1950s saw the manufacture of the first tubeless tires as well as the first appearance of fine grooves in the tire treads known as sipes (figure F). Siping contributes significantly to the tire to maintain traction even on wet pavement. Belted "wide oval" tires first appeared in the 1960s. Though they don't look wide by today's standards, they were a good bit wider than the tires made during the '50s (figure G). The current evolution of tires seems to be moving in the direction of wider treads and lower-profile tires that fit on wider wheel-rims. Some rims now measure 18 or 19 inches in diameter. In addition, there's a widening array of specialty tires available, including performance, ultra-high-performance, off-road, all-weather and snow tires.
RESOURCES :
Auto Repair for Dummies
Author: Deanna Sclar
ISBN: 0764550896
Tires, Suspension and Handling
ISBN: 1560918314
Author: John C. Dixon
(Society of Automotive Engineers
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