In a recent RV forum there was a question on tire inflation on Class A RVs. I advised, as I always do, that with knowledge of the tire size and actual measured load, I would check the published Load & Inflation tables and let him know.
While the poster did not provide the information I requested, he did ask a different question:
In your expert opinion, am I better off running 105 in front and 100 in back, per chart, or 110 all around in this heat?
The minimum inflation for an application is based on the tire size and the measured load it is supposed to carry. The Certification label states the GAWR, which is the most a tire should carry and the inflation needed to support that load. This is a DOT requirement. So the correct answer to your question on what inflation to run requires that I know the measured load on the tire and tire size or the inflation numbers on your Certification label.
Thanks. My main question is from a tire guy: What is the most over the minimum PSI without damaging the tire? I truly appreciate this site and all people in it.
My final reply to him was:
Tires can tolerate 100° F ambient and 65 mph all day long as long as the “cold” pressure is set no lower than the Minimum published in industry data books. I recommend that RV owners add 10% psi to the MINIMUM shown in the charts. You can set your TPMS High-Pressure warning level to +20% to +25% over the table minimum.
We tire engineers test tires to the published industry tables and test them at test tracks in Texas and Mexico, as well as in laboratories that are heated to 100° F 24/7. I would recommend against just inflating to the minimum and driving 80 mph when it is over 100°F.
I also recommend that people not guess at their tire loads. At a minimum, get on a truck scale and learn the actual load on each axle. Since we know that almost no RV has the weight split 50/50, side to side, I suggest you calculate 51% to 52% being on one end of each axle and use that load figure when consulting the inflation tables. (NOTE: We have seen some axles on large RVs being out of side-to-side load balance by over 1,000 lbs., and this is why “4 corner” weighing is recommended.)
Also, all tires on an axle should be inflated to the same PSI, and you should use a digital gauge that you have checked against a “master gauge” at the tire store. When I run comparisons of gauges, we see about 10–15% being off by over 5 psi. Check my blog for more posts on Load & Inflation: www.RVTireSafety.Net
List for people with tire questions
I really have a problem with people asking questions but not providing what I consider is the most basic information. So I recently published this list for people with tire questions:
- What does your Certification Label say for GAWR, Tire Size and Load Rating?
- Are your tires P-type, LT-type, ST-type or Metric (no letter before the numbers).
- Truck scale readings when the RV is loaded to it’s heaviest. Individual axle readings are better than the total if you have two axles. The weight should be when you are hooked up as if you were traveling.
- What is your normal cold tire PSI?
- Do you run a TPMS?
- What is your Low Pressure warning level set on your TPMS?
- Why are you changing tires?
- What are the new tires you are using (Size, Type and Load Rating)?
- What is your specific question?
I’m happy to answer your tire questions, but please provide the information requested in #1 – #9 so I can give you an accurate answer.
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.