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Thursday, October 6, 2016

How old is too old part 2

Last week I addressed the topic of tire age. Some are still asking why there isn't a better and clearer age limit on tires in RV use. It may help if there is a better understanding of the complexities of what is involved in making the prediction.

I think that most can understand that the numerous variables involved such as ambient temperature, operating temperature, load, and operating speed all can affect the "life" of a tire. Also there is the obvious variation in the numerous components and assembly practice of each tire itself. All of this adds up to an impossibly complex equation if trying to predict the life of a tire.

While many may understand that if a tire spends its life in Arizona, Texas, Alabama, Louisiana or Florida, it will have a definitely different life span than one that spends its life in New England, even if the load, inflation and speed were magically identical. I do wonder how many have even a passing understanding of the complex nature of manufacturing a tire as seen in THIS animated video. Actual shots of the process are here.  Here is an alternate view of the truck tire process, which would be essentially identical to what is seen in both LT and 22.5" size tires. If you watch only one video, IMO this 3rd one is the best and most informative.

Unlike materials like steel or aluminum, rubber is not a homogeneous material so even minor variations in the raw materials can affect raw material properties and ultimately tire life.

Here is a video showing the basic process of preparing rubber before it is applied to steel or polyester cords. Note these are videos of very low tech methods. Modern equipment is much larger and the process is harder to see as there is much more automation behind closed chamber shields.

The estimates of maximum tire life are based on assumptions of the variability of the tire and the variability of the use of the tire. The estimate must also consider the probability of the variables stacking up and the potential for the severity of the tire failure.

Some companies may feel that no greater than 0.5% probability of failure at 7 years is acceptable IF the tire is always operated in North America, never exceeds its max speed rating or is overloaded for the inflation in the tire. Another company may feel that less than 5% at 12 years is the goal.

It is also important to remember that only after thousands of tires have completed years of service can a company know if it made the correct calculations. I do not know of any company that is not constantly working to lower the failure rate or extend the usage time while at the same time trying to meet customer demands for better wear, fuel economy, traction, ride and lower cost, and the order of priority for these and other variables the customer wants in their tires.

While compromising safety is never a consideration, the rank order of the dozens of performance characteristics can have an effect on tire life.

Here is a challenge with hypothetical information. Would all RV owners be happier if they were told that the maximum age of tires was 8 years   BUT it would be illegal to operate on a tire older than 8 years or operate without a load, temperature and pressure monitor and recording system "black box" system and tire warranty would only be good 4 of the 8 year life?  Oh ya, the "black box" monitor system would add $500 to the initial cost of the RV and there would be a required annual fee of $75?

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  1. After see the first post, I am looking for this second, it is wonderful to understand the rubber manufacturing process. It is great to see that video!
    But I see the employees do not have the face mask to protect their lung, they must work in the lack of safety condition.
    Thanks for the article!

  2. Some videos are old so safety wasn't as much of an issue. Today when particulate and other chemicals are used various safety equipment is worn. I am not aware of issues with particulat matter or fumes in today's processes as those items were removed from tire plants in 60's and 70's.


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