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Monday, May 6, 2013

Defective tire or incorrect diagnosis?

I have been following a thread on a forum for an iconic RV. The company makes trailers that are all silver, but I won't name names. A few of those posts insist the tires are defective because first they failed and second because the owner didn't want to admit the possibility of some external cause as they want to find someone to blame. They will insist that there's "not a scratch on the sidewalls anywhere, and they have never hit a curb or anything else with them."  But somehow two tires failed after 9,000 miles.

The tire pictured here with a very obvious failure was identified as "Defective" by engineers at a large car company. I will cover the real reason in the next post.

I thought this would be a good opportunity to discuss the realities of tire failures and possible defective tires.

While tires are built individually, the various components are made in batches. Depending on the component these batches may be used in 100 to many thousands of tires. So let’s discuss how a "defective" tire might be made.

If it's a design defect then we should see the failure occur in a large percentage of the tires that are manufactured to that specification. Given that in regular production it is not unusual to see 10,000 to 1,000,000 tires made to a given specification it should be easy to see thousands or tens of thousands of identical failures.

A specification identifies which type of rubber is to be used for each of the 15 to 20 different components as well as the type of steel, polyester or nylon to be used. Now it is actually pretty unusual to have a design go into production that results in tires that will fall apart in service. Dozens if not hundreds of tires made to a new specification are tested before a specification is released to production. Additional testing is done by the producing plant to "qualify" the plant to make a specific tire. Even after a spec is released at a plant, modern quality control methods dictate spot checks of production tires. If you research tire recalls over the past few decades you will find that they are not tire design related but either service related or occur in relatively small batches of tires where there was human error in the producing plant on a single batch or two of component rubber not being made to spec.

Another thing that is basically true about tires made with an off-spec material is that they have a very high failure rate, very early in life, sometimes approaching 100 percent. Also the condition of the tires will be essentially identical. You will not see some tires throw a tread off while others have sidewall bulges. Sidewall bulges would all be of approximately the same size and location. If the error was, say, something like the wrong rubber used for the sidewall then I would expect almost all tires made with the wrong compound to suffer the same fate at about the same number of miles and that this failure would be early in life.

Next time I will show some examples of failures that were improperly diagnosed as “defective tires” by tire dealers and engineers working for the auto companies. The tire above is but one example.

3 comments:

  1. It's always the tires fault. I know you LOOKED at your tires yesterday and they seemed fine. Last week as we were getting ready to leave camp I glanced at my tires and one just didn"t look quite right. I took out the pressure guage and lo and behold I had just 32# in one and 70 in three. They hardly looked differant. 2 nails in one tire. I know, defective tires. Not armor plated enough.

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  2. The big question is... When did the tires pick up the nails and when did the air start leaking? I am sure it must have been 5' before you pulled into your driveway after your last trip so you never put even 12" of travel distance at any pressure less than 65 psi.

    At least that is what many people seem to think happens. I wonder how many people know that even at zero mph there is a minimum inflation required in tires when loaded.

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  3. Please consider that it may not be the tires at all. Our experience was that the manufacturer put on wheels and tires that were too small for the trailer. Since the mfg. sent us upgrades on all tires and wheels, we have not had a problem. We went through 13-15 tires in less than five years before we got the mfg. to admit what the problem was. Also, trailer owners...have you checked your frames lately. Frames that are too lightweight for the trailer specs are also a place where even the best of mfgs. cut costs.

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