Unfortunately, a great many untrained people are repairing tires these days, and the different types of operations and methods they use are astonishing. Training programs rarely reach many retreading outlets. This is due, in part, to the sheer number of retread plants in operation, but also because their labor turnover rate tends to be high. With improper tire repairs the No. 1 cause of tire failure, it's easy to determine where the problem lies.
Originally, the majority of tire ``punctures'' were caused by structural failure of the casing due to inadequate design or weak cord bodies. This type of failure is rare these days, and ``punctures,'' which normally cause a slow loss of air pressure, are nearly all the result of penetrations by sharp objects.
There is no practical way of preventing a hard, sharp object from penetrating a tire, especially when it is lubricated by rainwater, mud or snow. The presence of layers of cord reinforcement under the tread, including the steel belts, merely guide the penetrating object more effectively through to the air chamber.
Modern tubeless tires can absorb nails, and at times it is possible to continue driving with some safety because the inflation pressure diminishes gradually.
But the worst thing about getting a puncture is not the inconvenience of having to stop and take care of the problem, it's the damage that can be caused to the tire if you don't stop in time.
Driving with an underinflated tire can be a dangerous practice. At highway speeds and under full load, each revolution of the wheel distorts the tire and causes overheating.
Temperatures can reach 212 degrees Fahrenheit and cause internal deterioration that may not be visible externally, and which certainly cannot be rectified with an on-the-wheel repair.
Once the puncture has been located and the extent of damage assessed, the question arises as to whether it is worthwhile repairing the tire or whether it should be replaced with a new one.
I simply cannot understand the continuing widespread use of on-the-wheel repairs and wonder why the tire makers don't make a strong effort to advise against the use of on-the-wheel methods.
Is it because the industry spends too much on customer persuasion and not enough on consumer education?
It should be stressed over and over that on-the-wheel repairs are only a temporary, get-you-home method that doesn't allow internal examination of the damaged tire.
Such examinations are important, as there is no such thing as a standard puncture hole. Punctures can be caused by sharp objects that cut their way into a tire, blunt objects that tear their way into a tire, or sharp nails that usually make nice round holes.
Tubeless tires naturally compress around a puncturing object for a period, and at least partially seal around small objects of regular cross-sectional shape.
Subsequent movement and rasping action by the penetrating object tend to destroy the compressive effect and increase the size of the penetration. Air will seep between the plies and separation sets in-with subsequent failure of the tire.
An on-the-wheel repair with string or other such material may seal air in the casing, but it may not adequately seal the inner liner. Air pressure will seep into the cord body and lead to separations and excessive heat.
Some years ago I was involved in a series of tests for a variety of on-the-wheel repair products. Failures occurred after several thousand miles of service.
The excess material in string-type repairs wore through the inner liner and exposed the radial plies. Some of the other, more solid products caused splitting between the radial cords.
Others allowed moisture to penetrate the casing and cause rusting of the steel cords and degradation of the textile cords.
None of these methods were deemed to be satisfactory for permanent repairs.
With the widespread use of ``mini-spares,'' most motorists will opt to drop off their punctured tire to be repaired by the local service station because it is convenient and the repairman is thought to have repair know-how.
Yet we all know that the average motorist has little or no idea of what a proper tire repair is. That's why they get suckered into on-the-wheel repairs.
With these thoughts in mind, and despite the high cost of tires these days, more and more tire technicians are advising the purchase of a replacement tire-especially when it is not known how long a tire has been losing air while subjected to today's increased highway speeds and higher horsepower engines.
Why many repair shops fail to follow common sense regarding tire repairs is puzzling. But there seems to be complete disregard for the fact that we are an extremely litigious society. A lawsuit can wipe out a business if injury or death results from the failure of such temporary repair methods.
Our objective should be not to ``patch'' a tire but to permanently repair the damaged area. We should never lose sight of the fact that people's lives depend on our workmanship.