“The Rest of the Story” - Attention to details.

 Many of us have heard that phrase used as a preface to additional facts that sometimes do not make it into a story as widely published, but once the additional information is explained we learn that we do not always get all the important information  the first time around.

What brings this up was an item in an RV magazine I stumbled upon when cleaning out some old boxes of stuff. This is from Nov 2008 but the facts and information are still important today. The author is one of that small group of RV “experts” that make a living providing information on the Internet on just about all things RV. Sometimes they are answering questions about refrigerators, then they might be answering a question on holding tanks or plumbing. From my point of view it seems that they are quite knowledgeable about most topics but sometimes there are important details related to tires that don't always make it into their posts on tires.

The owner of a 5th wheel trailer had purchased a set of tires and offered that the tire store inflated the tires to 85 psi which was the “maximum” as molded onto the tire sidewall. The owner said he had heard that using the maximum inflation from the tire as the standard pressure was advisable and wanted to know the “rule of thumb” for the proper inflation.

He also wanted to know if he needed to reduce the tire pressure when he traveled to 8,000 ft elevations.

The “expert” correctly replied that the inflation on the tire was the minimum required to carry the load on the tire, he continued with the recommendation that tire loads be measured on a truck scale and then the inflation set based on Load & Inflation tables. There was no mention of ensuring that there was at least a 10% margin between the tire Load Capacity and the actual load on the tire. This recommendation to a trailer owner would address some of the unique side loading (Interply Shear) seen on multi-axle trailers which is significantly different than that seen on motorized RVs.

While I advocate that trailer owners get their rig weighed so they can confirm they are not overloading any individual tire, as it is not unusual for one tire or axle to be 500 to 1,000Ibs away from a theoretical 50/50 weight balance. I do strongly suggest that all multi-axle trailers run the inflation shown on the tire, which in most cases is the inflation shown on the RV placard as provided by the RV manufacturer. This will help reduce the side force  overload seen by trailers but not by motorhomes.

The expert did correctly advise that while the tire pressure will change with elevation, but said that unless the owner was checking his inflation daily, "as recommended", it was not necessary to adjust inflation when traveling to high elevations.

When I originally read this reply I was concerned and did send a letter to the expert pointing out the missed opportunity to educate RV owners about the importance of setting proper inflation, and that a stronger statement on more frequent or constant inflation checks by using a tire pressure monitoring system ( TPMS) was needed.

I do not consider daily inflation checks sufficient, especially for towables as too often the driver of the tow vehicle has no idea a tire is loosing air till it is too late to save the tire and there has been a "blowout" from a puncture or leaking valve which could cause thousands of dollars worth of damage to the RV. I also would not imply that when traveling to high elevations it isn't necessary to adjust your inflation whenever the inflation is checked.

As you can see the general RV expert provided mostly correct information, but he left out some considerations that I, as a tire engineer, do believe to be very important.

 

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