On an RV forum I saw some posts about tire failures:
There were some posts that mentioned the RV total weight capacity or Gross Vehicle Weight Rating (GVWR). Others were mentioning the total of the tow vehicle plus the RV trailer or Gross Combined Weight Rating (GCWR). Others were talking about tire load capacity.
One person responded with: “You need to pay more attention to just what acronyms are telling you. GCWR has nothing to do with tire inflation pressures. The tow vehicle and towed vehicle are individual vehicles and answer to their own standards and regulations.
“Maybe you should ask Roger why, during his working years with tires, the interply sheer problem was never corrected. (Interjecting a fear factor for attention purposes might be Roger’s goal.)
“Tire tread separations are a fact that trailer haulers must respect. Fooling around with RV trailer tire inflation pressures by using less than what the vehicle manufacturer has recommended is, IMO, counter productive.”
My response regarding interply shear
Since I was mentioned in the forum post along with the suggestion I might be spreading fear, I felt the need to reply, as follows:
Sorry, but fear is not and has never been my intent. I covered interply shear and how I discovered that it was different for multi-axle trailers than it is in motor vehicles in my blog post of Nov. 20, 2013, when I did the first of multiple posts on Interply Shear as it pertains to multi-axle trailers.
The fact is that Interply Shear is well known in the tire industry but not the unique forces imparted on multi-axle trailers. It was pure chance that I noticed the irregular path taken by a trailer doing a 180° U turn on freshly smoothed gravel (picture in the Feb. 22, 2018 post). That was my Ah-Ha moment.
While I was retired by the time I first saw the gravel path, I still had friends that worked with the high power Finite Element and vehicle simulation software and called in a couple favors. I asked them to run a simulation of a truck pulling a tandem-axle trailer through a series of “S” curves. All 8 tires were identical with the same load and inflation so we could end up with a comparison of trailer effects on tire belts vs. the normal interply forces found in all radial tires in motor vehicle applications.
Interesting discovery regarding internal shear forces
What we discovered after the overnight computer run was that in simple S turns, the belts on a multi-axle trailer were developing 24% higher internal shear forces than the tires on the truck pulling the trailer.
This goes a long way in explaining why tires in multi-axle applications have much shorter life and significantly higher failure rate than do tires in car or truck applications.
So, you see, science and facts can be used to point out why blindly following 50-year-old design decisions and regulations that are the foundation for the current ST tire regulations can be significantly improved upon.
Have a tire question? Ask Roger on his new RV Tires Forum here. It’s hosted by RVtravel.com and moderated by Roger. He’ll be happy to help you.