What You Should Know About Tires
DID you realize that the only contact your car has with the ground are the tires? Not only do they serve to soften your ride; they are vital in braking and in steering the car. But what if the tires are faulty?
Then traffic accidents may result; in fact, a large percentage of auto accidents are attributed to faulty tires. When you consider that hundreds of traffic deaths occur every day throughout the world, you can see how vital your tires are. What do you know about them and their care?
The chief tire ingredient is rubber, most of which today is synthetically made. In the United States about 60 percent of all rubber used goes into tires and tubes. However, the rubber in tires has various additives, basic ones of which are as follows:
Sulfur, to help vulcanize or cure the rubber. Carbon black, to add strength and toughness in resisting abrasion. Oils and tars, to make the rubber workable and to assist in mixing and blending it. Antioxidants and antiozonants, to help resist the harmful effects of sunlight and ozone, and thus give the tire longer life.
A modern tire also contains fabric, usually rayon or nylon. The compounded rubber is worked into the fabric between large rollers, producing rubberized fabric. If a tire were made of rubber alone, it would not be able to withstand the tremendous pressures and heat generated at high road speeds. It would distort and collapse.
Therefore the carcass, or body of the tire, is constructed of one layer after another of rubberized fabric. Each layer is called a ply. A two-ply tire thus has two fabric layers, a four-ply tire has four layers. The rubber tread is afterward applied.
The tread is the part of the tire that contacts the road. Its pattern is designed as a result of careful scientific studies. The tread must grip the road when cornering and braking, even in wet weather.
If you look at the tread of a tire you will notice that it has fairly wide grooves running the length of the tread; it also has smaller cuts called sipes running at an angle between these grooves. This design is particularly effective in wet weather. The sipes act like tiny wipers, wiping the water from the road into the bigger grooves, where it can drain away.
Different Designs and Retreads
There are two basic tire designs. The bias or cross ply, and the radial ply. The bias is the most familiar in the United States, whereas radials have been standard in Europe for fifteen years, and are increasing in popularity in America. The major difference between the two, as the name suggests, is in the way the plies are situated.
The fabric layers of the bias-ply tire are set diagonally to the tread and crosswise to each other. In the belted bias-ply tire a belt of material, usually fiber glass, is added under the tread. This belt gives improved handling and traction, and provides longer tire wear because it prevents the tread from squirming on the road. Of the 1970 American cars, 85 percent were equipped with these new belted bias-ply tires, whereas two years before only a few were.
In the radial-ply tire the layers of fabric run at right angles to the tread. Then an additional belt made of fabric or steel fits like a hoop around the tire, under the tread, giving the tread rigidity. The entire tread width is therefore in contact with the road at all times, resulting in less tread wear.
A retread is a worn tire that has had a new tread vulcanized onto it. The process starts with a careful inspection of the tire to make sure fabric body is not damaged. The tire is then taken to a buffing machine to remove all old tread, leaving the carcass intact. The carcass is next sprayed with a rubber solution. A machine then applies a slab of tread rubber, bonding it to the old carcass. Finally the tire is put into a mold and cured for about an hour. This is a less expensive way of getting a reasonably good tire.
The most important service you can give your tires is proper inflation. This will extend their life, saving you money, as well as increasing their safety. Your car owner’s manual will give the recommended inflation pressure.
Underinflation is one of the major causes of short tire life. When a tire is underinflated this causes excessive flexing, which creates heat and weakens the tire. Studies have revealed that a tire that carries eighteen pounds of air pressure, but which should have twenty-five pounds, will last only half of its normal life! If a person has been running his tires underinflated, the tread will be worn down toward the edges more than in the middle. On the other hand, more tread wear in the middle than toward the edges shows the tire has been overinflated.
It is important to check air pressure regularly; even the weather affects it. A tire will lose about one pound of pressure for every ten degrees drop in temperature Fahrenheit. It may be unwise to trust the gauge of the air pump at service stations; they are often inaccurate. A small tire-pressure gauge is inexpensive, and can be kept in your glove compartment.
Tires should be checked when they are cold, that is, before you have traveled more than a mile. This is because tire pressure will rise during running. A tire that is underinflated when cold may register above the recommended pressure when hot. But never ‘bleed’ air from tires when they are hot, for then they will be below the proper pressure when cool.
Proper tire care also includes carefulness in parking—not bumping into curbs. This can fracture fabric plies. Running over large stones or debris can do the same. Sustained high-speed driving, jackrabbit starts, fast cornering and hard braking all result in rapid tire wear.
It is wise, too, periodically to examine each tire for cuts or other damage that may lead to failure. Also check for stones, nails or other ‘foreign’ bodies that may be embedded in the treads. If neglected they may work through the rubber and cause a puncture.
Tires are a very important part of your car. And caring well for them, not only will save you money, but may save your life.