By Roger Marble
Are RV trailer tires exempt from the physical laws of the universe? What is so special about RV trailers that would make people think they are free from scientific principles and physical realities?
On an internet forum for owners of a well-known RV trailer company, there was a discussion on what the correct or proper inflation and load capacity was for tires on the company’s trailers. I jumped in with the following observations.
Tires list the maximum load they are rated to support and they also list the minimum cold inflation needed to achieve that load capacity. This dichotomy of “The Maximum is the Minimum” was covered in my blog on RV Tire Safety.
I really do not understand why people seem so afraid of running more than the minimum cold inflation needed to support the actual load.
I am in the process of working through the “Rule Making” documents from DOT when they set the minimum margins on inflation for cars, SUVs and trucks equipped with TPMS. It is noted that RVs were specifically excluded from this rule making. Could that be because the RV companies didn’t want to see any increase in costs even if it meant the product would have fewer failures?
No, that couldn’t be. No corporation would ever shave costs if the safety of the product might be compromised – would they?
The MINIMUM cold inflation a tire should have would be the level needed to support the actual tire load. They also established that the normal cold inflation should be at least 25% higher than the MINIMUM. Their objective was to minimize tire failures that might result in damage or injury. The DOT knows that tire pressure increases with temperature (2% per 10 F), and tire engineers know and design, and even depend on, this physical fact.
For some reason people feel it’s OK to have zero margin in their RV trailer tires. It wasn’t until 2017 that RVIA (RV Industry Association) started to specify a small 10% margin. Some people argue that the RVIA is not a real requirement as it isn’t a legal requirement. For RVs built before 2017, many RV trailers have certification stickers that specify ZERO margin or essentially zero margin as the tire capacity that was to be considered acceptable.
With the above as guidelines, I have to wonder why people continue to complain about having tire failures. You are making the conscious decision to ignore established engineering recommendations and safety margin guidelines. So, again, just what is so special about RV trailers that would make you think they are exempt from scientific principles and physical realities?
Have a tire question? Sign up for Roger Marble’s new Facebook Group: RV tire news, information and discussion, moderated by Roger. He’ll be happy to help you.
Read more from Roger Marble on his blog at RVtiresafety.net or on RVtravel.com.
##RVT983
I have issues with the outfits who sells and install tires. More often than not all they are really interested in is selling tires. I have yet to run into a tire shop than can weigh a rig. What is even worst the information they give you on how to take care of your tires is non existant at best. The motorhome manufactures are just as bad. I have found that the tires they put on the rigs are just enough to support the rig while it is empty. Load it up and then it becomes over loaded or is running at the max weight at all times. There is no safety margin. I have always try to stay on top of the tire inflation before I set out on a trip. Yet I have had tires blow out and come apart in which they do damage. I still remember one time I pick up the tread and took it and the tire to a shop to try to find out just what the hell happen. The only answer I could get from these jokers is “I DON’T KNOW” But they were more than happy to sell me a new tire.
Goodyear Tire Company recommends trailer tires be inflated to the maximum pressure stamped on the sidewall because they need stiff sidewalls to prevent heat buildup.
In my 24 year career as a military aircraft mechanic I learned alot about tire inflation. I refer folks to Roger when they need expert knowledge correction. I enjoy his articles.
I have never inflated trailer tires to the trailer manufacturer recommended pressures as I believe their recommendations are based on UVW and not GVW. Most people are traveling closer to GVW+. There is something in the female genes that says they MUST take everything they have at home and have the same in the RV. When we traded up to a larger 5th wheel I decided to weigh every thing I removed from the old one. Using the bathroom scale I removed 1073 lbs of which a 28 lb toolbox of mine was included, also a full set of cast iron cookware from the little cornbread baking skillet up to a 12” cast iron skillet. When we brought the new one home I used the same procedure in the loading process. We managed to get by with a 433 lb reduction. She didn’t like having to cut down her collection of cast iron skillets to a small one and a large one but perseverance finally won.
Bob, The RV mfg is required to select a tire size and specify inflation that can support 100% of the GAWR not the “dry weight or Unloaded vehicle weight. Your RV has a “Certification label” that is supposed to clearly state the GAWR for each axle and the complete tire size, including the Load Range. It is also supposed to have the MFG recommended cold inflation needed to support the GAWR. If you don’t have a sticker, you should contact the dealer/MFG and point out the violation of Federal regulation. Here is an older post from my blog on Certification Labels.
https://www.rvtiresafety.net/2011/05/certification-label-otherwise-known-as.html
(It looks like I need to do an update as the current label may look a little different than the examples in my post from 2011.)
Safe travels and thanks for reading.
After your reply I went out and checked, according to the owners manual cold inflation pressure is 65PSI. I checked the tire sidewall and maximum inflation pressure is 65PSI. Apparently the manufacturer hasn’t put any margin for safety into my tires.