A Soft Ride—Long Sought, Now Possible
By “Awake!” correspondent in Trinidad
SEVERAL thousand years ago, in the Mesopotamian valley, wheeled carts were used to transport goods and people. The well-made solid wooden wheels consisted of thick planks fastened together, and they were thicker at the hub than at the rim. Some even had metal rims or were studded with copper nails. Can you imagine the kind of ride you would have had on such a cart? Every stone or rough spot a wheel would pass over would be transferred to the passenger as a jarring jolt. This was a far cry from a soft ride.
About the middle of the second millennium B.C.E., military men decided that wheels could be used to an advantage in battle. Hence, crude and, later, very effective chariots appeared on the field of battle in areas where there were plains on which to maneuver. These chariot wheels soon were very well constructed. They usually had spokes—four, six or eight—and were complete with rims of metal or leather, or were nail studded. As a chariot was generally very light, a pair of galloping horses could get its riders over the ground at a fairly rapid rate. In such a chariot charge, every bit of uneven ground must have been bone-shaking.
Passenger Transportation Grows
Aside from being used to some extent for passenger transportation, the military chariot remained popular for centuries. In fact, it was during the days of the Roman Empire that its use as a military weapon lost favor, and it became restricted largely to the circus and races. During this time, wheeled vehicles for passenger service became more and more plentiful. The fine road system of the empire had much to do with this.
An early form of the modern type of wagon appeared in Denmark. The remains of one of these vehicles, known as the Dejbjerg wagon, has been found. Even crude wooden roller bearings were used in the hubs of this wagon.
Other peoples also made their contribution toward improving the wheel. To produce a better wheel, the Scandinavians used heat to bend the wooden rims or fellies. The Chinese seem to have been first in making a dished wheel. Hungary contributed toward the development of the coach, which made its appearance during the latter part of the Middle Ages. Nevertheless, a soft, comfortable ride still was a long way off.
Modern Improvement Comes
The 19th century, however, saw many developments that led to a softer, more comfortable ride. Some experimenting had been done with suspending the body of a vehicle by chains or by leather belts to take some of the jolting out of the ride. At the beginning of the century, steel springs were invented and applied to the various types of wheeled wagons and carriages of the day. A little later came the invention of macadam roads, which went a long way in making possible a more comfortable ride. But the really big breakthrough came in 1839, when Charles Goodyear accidentally, by the introduction of sulphur, changed raw rubber into an elastic material. This process, known as vulcanization, opened the way for putting a tire of rubber on the rims of wheels, making possible a softer and quieter ride.
By 1845, the Englishman Robert William Thomson patented a pneumatic tire to be used on the English brougham. It had an outer cover and a rubber inner tube. A set of these “Aerial Wheels” would last about 1,200 miles (1,900 kilometers) on a brougham. The public, however, was not ready for this tire and preferred to get along with solid-rubber tires. This situation continued on for some 40 years, until John Boyd Dunlop invented a pneumatic bicycle tire in 1888-89.
It was about this time that the automobile began to appear. A pneumatic tire was just what was needed to suit the growing development and popularity of this “horseless carriage.” Early tires were like bicycle tires, being just a single tube of canvas coated inside and out with rubber. They were not very durable, as the square-woven fabric caused a lot of friction and rapid deterioration. Clincher tires appeared in 1892 and were used for many years on some autos. These carried a high pressure. About 1900 this pressure usually was about 65 pounds (29 kilograms). The tires were small and so did not contribute much toward a soft ride. Nor did they last long, only about 2,000 miles (3,200 kilometers) at first. By 1920, this had increased to about 10,000 miles (16,000 kilometers). Then came the steel-spoked and disk wheels that were smaller in diameter and had tires with a bigger cross section and much less pressure. The “balloon” tires from the early 1930’s onward did last longer and were much more comfortable. By 1957 a tire could last as long as 35,000 miles (56,000 kilometers) under favorable conditions.
How Tires Are Made
Have you ever wondered how a modern tire is made? My opportunity to find out came when the manager of the Dunlop factory in southern Trinidad arranged for me to tour their plant. A parting suggestion over the telephone was: “Be sure to wear some old clothes.”
Entering the plant with my guide, I at once realized why the old clothes were suggested. Instead of there being a shining array of machinery, everything had a dingy, black appearance. Why was this? Well, a principal component of a tire is carbon black—and is it black! It is a fine powder that penetrates everything that is not closed off.
As I passed by large piles of various tire components, it appeared that I was in a large chemistry shop instead of a tire factory. The guide explained that many different chemicals are used in making a modern tire and that these chemicals are varied in amount and kind to produce the type of tire suited to perform well under the road conditions that a driver is likely to encounter. Some tires use much natural rubber. This is because natural rubber dissipates heat better than do synthetics and in severe cold also stands up better than do synthetics. However, since its introduction in the 1930’s by the Germans and in the United States by DuPont, synthetic rubber has been used in ever-increasing amounts. For this plant, sulphur comes from England, carbon black from Venezuela and natural rubber from Malaysia, while synthetic rubber comes from the Netherlands. Rayon and nylon cord may come from Japan, Germany or England. So, making tires here is really an international project.
The first step in making a tire is to mix all the polymers and other compounds or chemicals in a huge mixing machine called a Banbury mixer. A sample of the mix is tested in the laboratory to determine whether it has the characteristics desired for the particular type of tire being manufactured. A rubber can be produced that will grip very well on a wet road but may not do well on a dry road. It may have high rolling resistance and not wear well. So a compromise must be made. Most roads are wet some of the time and dry at other times. The mix must result in a tire that gives reasonably good service on a variety of road surfaces. Many different mixes are produced by this machine. Now the material is fed through an extruder to make the tread and sidewalls of the tire. Again what makes the tread may be different in composition from the sidewall in order to meet the different situations encountered as the tire revolves and also to withstand sun and weather conditions.
Over there is a complicated piece of machinery. What does it do? Fabric is being fed into the machine to produce the plies that make up the carcass of the tire. Rayon cords are used in many tires, as are cords made of nylon and, more recently, polyester. Why is it that the cords running lengthwise (the warp of the fabric) are so much thicker and more numerous than those running crosswise? Well, that is to prevent heat buildup from friction when the tire is revolving. This machine coats the plies with rubber and cuts them so that they will form a crisscross pattern in making up the casing. This is the oldest and most common type of tire in use today. If you were to cut such a tire in two and strip back its tread, you would see these angled plies. These are the cheapest and the easiest tires to manufacture. They perform well and last for many miles but do not do as well as a more recent type that has become very popular in many countries.
A short distance away a workman is making cross-ply tires. The plies are put on layer by layer, with rubber solution being added between each ply. Why only two plies on passenger-car tires when we used to have four or six? The more plies, the more friction and the quicker the tire casing deteriorates. Besides, modern cords are much stronger than the old cotton cords of former years. The cooler a tire runs, the longer it lasts. The plies are wrapped around the wire hoops called the bead, and some chafer strips are added to give more strength where the tire fits the rim of the wheel. Now the tread is bonded to the casing, and the tire is complete. Complete? Why, it looks like a little barrel, anything but a tire! Oh, yes, it must go into a mold to be shaped and cured.
Heat and pressure complete the making of the tire. After a curing time in the huge molds, out comes a brand-new tire. Notice the tread. There are many designs for various purposes. In the early 1930’s, a tread of round knobs appeared, to be used for driving in the rurals off the highways. To a large degree, it did away with the need for chains. Later came treads with large lugs (to be used in snow), and then tungsten studs were inserted into the tread to make driving on the ice safer. In Trinidad we have neither ice nor snow, and so treads are smoother and give a softer, more silent ride. There are large grooves running around the tire, with many small slits or sipes running crosswise. These are to drain off water and give the tire better traction and cornering ability. You will do well to choose a tread to suit your driving needs, perhaps a winter and a summer set of tires in some climates. Remember, heavy treads make noise on a highway or an expressway and do not stand up well at continuous high speed.
Now, we see another type of tire being made, and the demand for it is increasing. It is the radial tire, so named because its plies run at right angles to the circumference of the tire. The radial tire is very flexible in the sidewalls but rigid in the tread due to its casing and a belt of several cross-plies underneath the tread. Because of this characteristic, it is a safer tire under most driving conditions, and it usually outlasts the cross-ply by many thousands of miles. The radial tire is more difficult to manufacture and so is more expensive. Nevertheless, there is an increasing demand for it.
A third type of tire is the belted cross-ply that is not made in this plant. A hybrid between the cross-ply and the radial, it is popular in the United States and other countries. The belted Polyglas tire has a casing of polyester cords and two belts of fiber glass. And, of course, there are the popular steel-belted tires.
After manufacture, tires are checked for roundness, balance and other requirements. Most tires with brand names will give good service if used for the purpose for which they were made.
As is evident from this tour, man has come a long way in making it possible for all of us to enjoy a soft ride. But whether it will be a safe ride largely depends on the drivers. Hence, for a safe ride, a person should buy tires to suit his driving needs and should drive to suit the tires he buys. Additionally, excessive speed, drugs, drunkenness and carelessness must be avoided.
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Fabric or Rubber