Despite the many thousands of printed words on the subject-and countless training programs and seminars-improper puncture repair techniques are still being practiced: sometimes willfully; sometimes ignorantly. Punctures are the most common form of damage to any pneumatic tire. In most cases it's simply a small hole that lets the air out; usually there is no structural damage to the tire body. Yet misinformation still seems to abound concerning this most common repair.
During my years with Michelin, I was often concerned by the attitudes of many repair people during training workshops. It was not unusual to hear comments such as: ``Yeah, I know that you have shown us how to make a safe, permanent repair, but my boss tells us not to demount flat tires. It takes too much time. Just plug the hole, it will hold air for a while.''
With such mindsets, is it any wonder why we are plagued by lawsuits?
A tire is only as good as the air pressure in it. Without those few pounds of air pressure, a tire can no longer work and becomes a large, useless lump of black rubber. It is not the tire structure that supports the load; it is the compressed air. The air produces a stress on the tire body, and it is its behavior in the casing under this stress that determines the final properties of the tire.
Ever since the earliest days of the pneumatic tire, nails have been a tire's biggest problem. There is still no way in which a sharp nail-like object can be prevented from penetrating the tread or sidewall rubber of a tire.
Nowadays, most nails are at least 20mm (3/4 inch) in length, and new passenger tires are somewhat less than that thickness in the tread area. So you can see that most nails will fully penetrate most new tires.
Some surveys also have shown that as the tread wears down, there many be some increase in punctures. And a wet nail meeting a wet tire is ideal for a puncture, since water is a good rubber lubricant.
A vehicle's rear tires experience about twice as many punctures as do the front tires. Sooner or later, a nail lying on the highway will be disturbed and flipped backwards toward the rear tires-by the tires on a preceding vehicle or by a vehicle's front tires. If the nail happens to catch the tire at just the right angle, it will penetrate the tread or, less frequently, the sidewall.
We must accept the fact that penetrations will occur and the compressed air will escape: sometimes quickly; sometimes slowly.
Most motorists have little practical experience in coping effectively with a punctured tire. They may not be aware of a tire going flat because modern suspension systems are good at isolating the driver from the highway surface. Add power steering and all road sensation is lost.
I've been called upon to examine countless numbers of tires in the past, many of which failed due to bad puncture repairs. You wouldn't believe some of the shoddy workmanship I've seen-some of which caused loss of lives when the repairs failed!
Inspecting a failed tire is much like examining pieces of a puzzle. When you see a particular kind of failure for the first time, it's hard to define. It's more easily diagnosed the second or third time you see it.
Quite often you get a tire torn into many pieces. This presents a three-dimensional jigsaw puzzle, as it is necessary to assemble all the pieces in order to get a clear picture of the order of damage.
This technique was exemplified in the World Trade Center bombing case, when two tire experts were called upon to examine 19 fragments of tires found in the wreckage.
Manuel Zambelas, a senior field engineer for Michelin North America, explained in considerable detail how the make of any tire fragment can easily be determined, as can the reasons for tire failure. ``Whatever you do to a tire, the tire will tell you,'' he said. ``All you have to know is how to read it.''
James Gardner, an engineer for Bridgestone/Firestone Inc., showed the jury how he reconstructed a tire from the pieces of rubber and steel belting found in the rubble. By using the fracture lines of the fragments, the pieces of lettering and tread elements, he was able to figure out what part of the tire the fragments came from.
Even when a tire is shattered into small fragments by a bomb explosion, experts knowledgable about a tire's characteristics and the way it interacts with the vehicle and any of the other tires on the vehicle, can determine exactly what happened to cause failure of the tire and why.
I mention this because if you are tempted to use short-cut methods of repairing, you can be sure that it will be found out if it results in failure.
And tire failures, particularly if they involve personal injury or death, lead to lawsuits-big-buck lawsuits.