I expect you may have noticed, and perhaps even been concerned about, the amount of tire debris that litters our nation's highways. I take a keen interest in these remains of failed tires, as tire problems have been my bread and butter for many years-and those problems become all too common in the warmer months. Driving home from New York's Kennedy airport the other day, I had just pulled alongside a large truck, when I heard a loud bang and my car was peppered with bits of rubber. This was not a surprise since I had been smelling hot rubber for some distance.
Even though the tire was an original tread tire, I assumed a retread would be blamed. That's been an ongoing problem, as too many motorists are of the opinion that retreads are the culprit. They believe retreads don't stand up to today's service conditions.
I had just returned from traveling more than 2,000 miles in the United Kingdom and Ireland, where I could count the amount of tire debris on one hand. So it was shocking to see enough tire debris on my 90-minute drive home to fill a small pickup truck. Why should this be? Why such a big difference between Europe and the U.S.?
One reason may be that economic pressures in our country have forced many tire users to economize by cutting back on maintenance-and tires are a high maintenance item.
It is not all that unusual to find trucks in Europe equipped with inflation monitoring devices to warn of low tire pressures. They also use larger-sized tires.
In a number of instances, I noticed areas along motorways and turnpikes where inflation can be checked and corrected. Obviously, the European user devotes more attention to proper inflation and maintenance.
Sorting through roadside tire debris is a dirty job at best, and it's one I've done often. Of course, you will find remains of retreads there, but not a disproportionate amount. And perhaps even more important, the retread rubber is still firmly affixed to the section.
Even if retreading did not exist, I believe there would be just about the same amount of rubber on the road.
So what is the cause? I'm afraid it is our old enemy: heat-heat caused by underinflation/overload.
The rubber-to-steel-cord bond seems vulnerable to the effects of heat, and the results are always the same: separations, tensile loss, chafing and often a burst.
Most tires don't fail because they are defective or punctured by a sharp object on the highway. They fail because they don't have the right amount of air in them.
The main function of the tire body is to support the load to be carried while at the same time providing adequate riding comfort. In order to do this, the casing must have ample resistance to fretting fatigue, and good, permanent adhesion to rubber.
When applied to a steel cord casing, ``fretting'' is a term used to signify the wearing away of metal from individual filaments during service. It is caused by mutual friction under high contact pressure. The result is that the filament section in the fretting areas is diminished with a resultant reduction of tensile strength.
When a tire is punctured and runs without air pressure, the steel cords may become crimped due to the weight of the vehicle on the flat tire. The load is transferred from the rim to the distorted innerface of the tire bead/lower sidewall to the inner surface of the casing beneath the tread, thus crimping the cords.
Also, with rubber rubbing on rubber, high frictional levels develop, and the low thermal conductivity of rubber contains the heat within the tire.
Surveys have shown that 23 percent of punctures have been present more than 60 miles before they were detected-and traveling 200 miles before a puncture is detected is not unheard of. Fifty percent of deflations were discovered when the vehicle was stationary. Thus it should be quite obvious that by the time a tire is removed for repairing, the body cords may have suffered damage.
Tensile tests on steel cord removed from radial casings after their first tread life indicate that the upper and lower sidewall areas are those most subject to reductions in tensile strength.
These, then, are the areas that require special attention when examining radial tires prior to retreading or repair. Also, adhesion breakdown is concentrated mostly in these areas as well.
Lately, much attention has been focused on the so-called ``zipper'' failures in radial truck tires. Some have opined that the product is at fault; that the steel cords do not have enough flexing resistance for today's needs. If this is so, why are such failures are far less common in Europe? With worldwide distribution, the products are the same, with the same construction.
A puncture, or new puncture repair, can usually be found in tires with these ``zipper'' failures. This confirms the fact that the tires were run underinflated or flat for some time before reinflation.
Even though the modern radial tire is the best ever produced, it still needs proper care and attention during its service life.
Let's not be too quick to blame the product before a proper analysis of use.