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Friday, August 13, 2021

Consumer Reports on RV tires. Helpful or fear mongering?

In my opinion.....

I had someone point out that the Sept issue of CR had a couple of pages on RV Tires and wondered if I could offer my opinion.  I do not subscribe to CR, as I have been less than impressed with some previous articles over the years. But I went to the local library and borrowed a copy.

I just finished the six-page article and will start off by saying my opinion of CR and their information on tires has not changed. "Danger on wheels" might give some the impression that this expose is based on a broad investigation into tires in RV application, when in fact almost the the entire article is on a single line of Goodyear tires that was in production 20 years ago. The G159. There is a lot of information on lawsuits and lawyers, but I found no hard data on tire durability or test data or failure analysis from CR.

While I have no personal knowledge of the G159 or any specific failures of the subject tire I was disappointed that the only warning CR provided was that tires should be removed from RV service "at 10 years old from date of the manufacturer".

As an engineer, I would prefer to set aside claims and innuendos and focus on facts and data. CR did offer what they called "9 Tips for safer RV travel". Of these only three even mention tires. One is the recommendation to replace tires that are 10 years old. Readers of RVTravel.com and of my RVTireSafety blog already know that 10 years is the MAXIMUM tire age with shorter usage time often recommended. Some are as short as 3 years in certain applications.

The article did point out that "about 40,000 G159s" were placed in RV service and that 72 RVs suffered tire failures. Given that 22.5" wheel size would suggest Class-A usage with a normal 6 tires per RV those numbers suggest over 6,000 "sets" of G159 were applied and possibly as few as 1.2% of RVs suffered tire failure.  No mention was made of how many of the 72 failures were the result of under-inflation, overloading, puncture, or impact. I too often see that any tire failure is blamed on the tire yet very few of those claim include any forensic inspection or identification of the mystery "defect".

A second recommendation from CR was to invest in Tire Pressure Monitor System. I completely agree that every RV should be equipped with a properly programed TPMS. They said that "The better systems involve fitting a sensor inside the tire." I wonder what testing CR did to arrive at that suggestion. Where is their data that supports the notion that internal to a tire somehow performs better than the more normal external, valve stem mounted sensors? I have never heard of CR doing any long term, direct comparison testing and evaluation of the different TPMS application as I have been doing for the last three years.

It is a bit of a stretch to suggest that "balance the weight in your RV" to reduce tire wear is a strong safety recommendation. They do suggest that the weight in the RV should be based on the capacity of the RV but no specific mention of confirming that no individual tire should be measured to confirm its loading. They didn't even educate their readers on how to know the weight limit on their tires.

Is there a technical problem with the GY G159? I do not know and the CR article only uses inference and suggestions that the ire was "related" to or "associated" accidents but I saw no evidence of what the claimed "defect" might be or if there even is one in the G159. There is a small mention that some owners might have lowered the tire inflation but no mention if that act resulted in tires being overloaded.

In my opinion, CR might get a few additional sales of their magazine but the article certainly did not offer any insight into how to prevent tire failures in RV use or into the importance of never overloading or under-inflating tires.

##RVT1013


Friday, August 6, 2021

Should I run ST tires on my trailer or can I use LT type?

 When it comes time to replace your tires on your RV trailer you may have a few options. Sometimes you may also be confronted with a limited supply problem that limits your selection. What can you do? What are your options?

Now I am assuming you have followed the general instructions to get your RV on a truck scale and as a minimum confirmed the load on each axle when the trailer is loaded to its heaviest. I have numerous posts in this blog on scale weights and how to calculate and estimate the load on the heaviest individual tire

So knowing you need a tire that can support at least 115% (125% is better) of your measured or calculated heaviest load you are ready to start shopping.

I had one reader express some concern about what he called "Sidewall Shear" forces and thought a stiff sidewall would be a better selection. I have no idea how he was going to measure the inflated sidewall stiffness and pointed out that un-inflated sidewall stiffness was not a reliable predictor of the inflated stiffness.

Here is what I told him:

I would not worry about "sidewall shear" as the real culprit for belt forces is Interply Shear at the steel belt edges which can lead to a belt separation.
Sidewall failures, which some confuse with "blowout" is the result of running at highway speeds with significant (40% to 60% or more air pressure loss).

THIS post shows the forces that cause belt Interply Shear. Don't be mislead and think its the sidewalls that are being overloaded. It's not.

You can get warned about the Sidewall Run Low Flex with the use of a TPMS that is properly programmed to alarm as soon as air pressure drops below the level needed to support the measured load on your tires. This comes from scale measurement and consultation of tire Load & Inflation tables.

Belt separations develop over hundreds to thousands of miles. A TPMS will not warn of impending belt separation BUT sometimes it is possible to "see" indications of possible or probable belt separation with a close visual inspection to check for run-out. Either Radial or lateral. I posted a link to a video on a "Free Spin" inspection in THIS blog post.

The GY Endurance tires I have inspected included Nylon or Aramid belt cap in addition to the 2 steel belts. If you find an LT type tire that can support 115% or better of the scale load on your heaviest tire that might be an acceptable alternative if it also has Nylon or Aramit cap belt.  LT tires have to pass more difficult DOT testing than ST type tires so that should give us the confidence to use those tires in RV applications.

Finally, you need to limit your MAX operating speed to 75 mph with LT type tires and to 65 with ST type tires. Even though some ST type tires have a "Speed Symbol" letter that implies speeds higher than 65 we need to remember that the test for those speeds is only 30 minutes and in reality the Speed Symbol is really just an indication of high heat resistence. The load capacity of ST type tires is based on a formula that specifice 65 mph as the max operational speed.

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##RVT1012