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|The Modern Tire
Compiled by Ali A. Karim (Jeddah, KSA)
|History and Evolution
A modern tire contains up to 50 basic raw materials, from carbon black to zinc oxide, 15 synthetic rubber combinations, man-made fibers, and high-strength alloy steels. The material must be strong enough to support cornering, acceleration, and braking loads, yet supple enough to absorb bumps. The manufacturing process that converts all these raw materials into a modern tire is just one step short of pure magic. It wasnt always that way; Fred Flintstones "tire" was nothing but a chunk off the old stone wall.
The first real breakthrough was the invention of the pneumatic tire, which dates to Robert William Thomsons English patent of 1845. That patents description of the function of a pneumatic tire still applies. It reads in part: "the application of elastic bearings around the tires of the wheels of carriages a hollow belt composed of some air or water tight material inflating it with air whereby the wheels will, in every part of their revolution, present a cushion of air to the ground."
The first pneumatic tires were built for bicycles. Things got better, of course, and in 1896, a Leon Bollee automobile was offered with Michelin pneumatic tires as original equipment (OE) - the first vehicle so fitted.
Early in tire development and through the 30s, the cords used in tire construction were generally cotton-based. In 1937, Michelin introduced a revolutionary truck tire called the Metallic, whose four plies of steel cord replaced as many as 10 plies of cotton. This truck tire was the beginning of steel-belt construction and changed the industry.
In the 50s, Michelin introduced the first passenger car radial, the Michelin X. Many refused to ride in a car equipped with the X tire because it looked under-inflated, but the little Michelin with the bulge in the sidewall turned out to be the forerunner of a superior breed of tire. The radial revolution had begun in the earnest. Passenger car tires are almost universally radial construction now, and the range of tires available is staggering.Technical Aspects
Technology has now progressed to the point where tire and car engineers collaborate to tune tire and car to work in unison. This makes it imperative for the car owner to understand that changing to different tires is not as simple as it appears. An improper choice can negatively affect vehicle performance and, worst case, even safety.
Ultra-high-performance tires have made enormous strides in traction (grip)and stability, but like most other things, tire design is the art of compromise. Traction on dry pavement requires the maximum amount of rubber in contact with the pavement. A thin tread reduces heat buildup at high speeds, which allows the tires to live at sustained high speeds. On a wet surface, however, a tire without tread has all the stability of the stock market. Street tires have tread patterns, sacrificing ultimate traction for wet stability. Such compromises exist in all areas of tire design. Lower aspect ratios (ratio of the height of the tires cross section, to its width) increase response, steering feel, and stability, but degrade ride comfort. Softer, stickier rubber compounds can increase traction dramatically, but wear much faster. Stiffer sidewalls increase steering precision and feel, but transmit excessive road shock to the vehicle. Radial construction allows the contact patch to maintain a better grip on the road surface, compared to less compliant, belted tires, and so on. Every parameter settled on by the tire engineer requires at least two compromises in other areas.
Tires designed for low-traction (wet) conditions have diametrically
opposite requirements. They need deep tread grooves to channel the water away from the
contact patch, high-void ratio (ratio of tread to grooves) to cut through the water and
down to the pavement, and high aspect ratios to increase ground clearance. The long, thin
contact patch also reduces the tendency for the tire to aquaplane (a dangerous phenomenon
where the tire water-skis, losing all traction). In addition to the High Performance
and Luxury tires, new tread designs and rubber compounding techniques have helped in
the development of All Season tires which are good on wet as well as on dry
roads, and even manage acceptable performance on the snow. These new generation all-season
tires have had a lot of energy expended on making sure theyre not noisy. Tires make noise
in two ways: a low frequency noise from the tire striking the road and a high frequency
sound from the air being squeezed out of the tread spaces as the tire compresses, rolling
over the surface.
At tire replacement time, an owner faces a bewildering array of choices, and getting good product information isnt always easy. The simplest solution is to stay with the same brand and size as supplied by the manufacturer. These tires have good all-round capabilities, but arent outstanding at one task. If an owner is willing to give a little on some tire parameters, he can gain significantly on others to better tailor the tire to his exact needs. Those willing to explore the cornucopia of tires available can increase cornering power, directional stability, braking potential, wet traction, and durability, while altering a cars appearance dramatically. But dont rush out with wallet in hand just yet there are some definite pitfalls. The engineers who designed your car took many factors into consideration when specifying original-equipment (OE) tires, from both size and capability standpoints. Changing tire / wheel size has a ripple effect that can hurt many areas of performance, and in some instances actually may be dangerous. It is recommended that any tire / wheel upgrades be done with the help of a competent shop that thoroughly understands all the ramifications of the changes and guarantees its work. The upgrade does not have to be for handling or styling reasons many people upgrade tires to increase load-carrying capacity; obtain better traction in mud, snow, or ice; or just for safety reasons. Tire Code Nomenclature
Todays tires have typical designations on their side-wall which can be understood as follows:
Section Width / Aspect Ratio, Rim Diameter, Load Index, Speed Symbol
for example: 205 / 60 R13 85 H
205 : Section Width (measured in millimeters)
60 : Aspect Ratio (ratio of the height of the tires cross section, to its width)
R13 : Rim Diameter (measured in inches)
85 : Load Index (Service Description, refer to Load Index table)
H : Speed Symbol (Service Description, refer to Speed Symbol table)
Load Index Table:
Note: Consult tire manufacturer for maximum speed.Final Word
The remaining question of brand (and model) selection is possibly the most difficult of all. Wading through the tire manufacturers claims is a formidable task, made more difficult by the glowing terminology that makes even the most miserable rim-protector sound like an Indy 500 pole-sitter. The bottom line is to treat tire buying as you would a new-car or other major purchase. Do research before starting. Know what brands and sizes are in your price range. Get out there, examine the tires, check their availability, and compare prices. Ask questions and try to get the manufacturers brochures. The more informed you are, the more satisfied you are going to be with your purchase. The right set of tires can make a tremendous amount of difference in your car.
Source : Motor Trend - Performance Car Buyers Guide
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