The topic of tire pressure seems to never die.
I just ran across a post from an enthusiast in Europe who has the “hobby”(??) of worrying about tire temperature and pressure.
He started out a few years ago by developing his own Load and Pressure formula, which is fine if that is what he finds interesting. But he then published the results of this new equation.
Now, if someone wants to play around with the established worldwide tire industry standards, that is up to them. The problem I have is that it is hard enough to educate RV owners on the importance of using the established tables. We do not need to add confusion from an individual, no matter how well intended, who is not a tire engineer. Even with my 40+ years of experience in tire design and testing on tires used on trucks, passenger cars, and Indy cars, I rely on the industry-published standards tables like this:
I also confirm with similar standards from Europe and Japan when necessary.
Yes, there are companies and people that do not understand tires and they think there is some “magic” temperature, when the major tire companies ALL agree with TRA, ETRTO and JATMA (in picture above) that ambient is the only correct reference temperature.
In the U.S. there is a very large tire retailer, Tire Rack, that focuses on high-performance tires but also sells regular tires. For years they said that pressure increases by 1% for each rise of temperature of 10 F. After I contacted them a few years ago and sent them a link to my RVTireSafety.net blog, they corrected their information to the much more accurate 2% for each 10 F.
There is a relationship between tire temperature and pressure
While there definitely is a relationship between tire temperature and pressure, most people have been led to believe that their TPMS is reporting the temperature of their tire. This is just misleading information. The problem with being concerned with tire temperature readings from TPMS is that the temperature reported by TPMS is actually the temperature of the metal wheel which is conducting heat from the metal hub and brakes. If a TPMS warns of high temperature, it usually means there is a mechanical problem with wheel bearings or brakes.
If there were a problem with an increase in the temperature of the tire structure it would show up with an increase in pressure long before there would be a meaningful increase in the temperature reading.
RE tire pressure increase: If the cold pressure has been set correctly, i.e., based on measured tire loading, and the cold pressure is set to no lower than the pressure for that load in the tables, there should not be a pressure increase of more than about 20% unless you are speeding, i.e., higher than 65 to 75 mph for tires in RV usage. I have found that if people run 10% more than the minimum pressure specified in the tables for their measured load, they will only see the pressure rise of 10 to 15%. Not everyone can run that +10% pressure because they would exceed the max wheel psi. These folks will need to reduce their tire loads.
Check out my Blog www.RVTireSafety.Net
Have a tire question? Ask Roger on his RV Tires Forum here. It’s hosted by RVtravel.com and moderated by Roger. He’ll be happy to help you.
Read more from Roger Marble on RVtravel.com.
We use a infrared thermometer for tire temps. It is amazing how much heat they absorb on a hot day in the desert. We do use your +10% air pressure recommendation religiously.
I imagine not many folks carry such charts/books to go by even if they check their own tire inflation pressures. Nine times out of ten or more often, if a person inflates tires to listed sidewall pressures cold, they will be fine if they have not exceeded the weight rating of each axle or at least exceed the GVWR. They might endure a harsher ride from a tire inflated higher than need be or optimum. And while tire inflation pressure might not be what everyone monitors constantly, tires often tend to be found lower than ideal chart/decal or sidewall pressures when checked. Heat can increase tire pressure, but tires almost always slowly lose their air. No tire should ever be installed on a rim rated at less than maximum sidewall tire pressure. Which can happen when a trailer owner goes from a load range “B” tire to a load range “D” tire. Keep axles, springs, wheels and tires all compatible with each other.
I met and talked with Roger at an FMCA event. It was memorable. He didn’t change my thinking about anything, but he did convince me that there are many that have the basics wrong. That is a campaign I am still waging. Every RV event should have people asking how owners determined the pressure that their tires should have. Those that say they use the maximum on the tire side wall should get hit with a (soft) hammer. This is a remarkable common answer. Those that say that they had the coach weighed and referred to the tire table should get a chit for free beer.
I’d never heard of a percentage increase but in my 60 years of driving it was always “For every 10 degrees of F increase in outside temperature it meant 1 PSI increase in tire pressure”. It pretty much works out the same for a tire pressure of 50 PSI, where a 2% increase would be 1 PSI. For an 80 PSI tire pressure 2% would mean 1.6 PSI increase.
Your initial complaint is what I see as a huge problem with this internet “information highway” – so many (can we make a contest of how many exactly?) of the new generation of RVers think it’s perfectly fine to query their peers in FB chat groups, take the best answer and run with it. Oh sometimes not the best answer, but taking the answer that fits their idea best.
Then, there are those who are self-proclaimed “experts” because they live full-time in the RV or because they’ve had a lot of blowouts (but don’t take responsibility because, “China bombs”!).
I feel like the Geico commercial “we know a thing or two because we’ve seen a thing or two” – some take that as license to share their “knowledge” even though it’s only based on their experience not always fact.
Yea…I think thats Farmers Insurance, not Geico.
He probably got his tire education from another internet “authority”.
Just wondering, any easy way to find out the wheels ability to handle a max tire pressure before blowing the connection?
my Tires pressures are based on your industry charts. Sorry that I missed your talk at Perry.
Very busy managing a parking team, helping get everyone sited.
Some cast aluminum wheels do have a “Max psi” rating marked on the back side. I do not recall seeing many steel wheels with their max psi rating. The best is if you can find the supplier of that wheel but that can be difficult to impossible. I can only suggest that you look at the psi number on your RV Certification label. If you have a tire inflation number of xxx Psi 80 on any of your tires, then the safest thing to do is to figure that that “xxx” is the “max” rating unless you can get numbers, in writing from the RV MFG or wheel Mfg.
Our Chevy P30 RV with 19.5 x6″ steel wheels has 100 psi embossed in them. Always worth a look see during a tire rotation. We also use that time to inspect the rim and tire for damage. We clean them as time permits.
Tom, Sorry you could not make it at Perry. I am giving 3 seminars on tires at Gillette FMCA Convention Aug 23 – 26
Good day Tom/Roger: I have a 1964 Class A with steel wheels manufactured and engraved, “Firestone ZT”. I found a Tire and Rim specification sheet which indicates these coded wheels are rated for 2,780 lbs and max. pressure of 95 psi. I am not sure if this is cold Inflation pressure or the maximum pressure regardless of ambient or tire temp!