RV Tire Safety
with RV tire expert Roger Marble
Question:
Do you think the tire pressure issue will ever be resolved to people accepting the values recommended by the tire manufacturers based on actual loading? Or will some always be confused between the tables, the placard and quotes of Federal Motor Vehicle Safety Standards (FMVSS) from some on the forum? It seems so simple and logical, but some just don’t get it. I still think a sticky written by you could settle the issue, but the moderators disagree – I suspect a concern for liability for the forum to advise something that contradicts the MH placard.
I have a question for you about my RV. I carry 5 psi above the minimum for the load on my steer tires on a 60-degree morning at 1100′ altitude. When traveling, I had a morning at 5000′ and temp in the upper 30s. This produced a pressure of 1-2 psi below the minimum. I was going to be traveling into a warmer climate (95 degrees), so did not adjust pressures. This type of condition can happen when we are traveling. I don’t want to chase the pressures, so if traveling into warmer weather, I just go and watch the TPMS. I don’t feel this is a problem but wanted your thoughts.
Thanks for your thoughts and time.
Answer:
Not sure if there ever will be a resolution to the “Inflate to the placard” versus “Inflate to the actual tire load.” I would liken this to the “change oil every 3,000 miles” versus “change when the car’s computer advises.”
DOT has a goal of trying to make things simple and keep people safe. DOT also knows about the data that indicates that over half of the RVs on the road today have one or more tire overloaded (either too much load or too little air for the actual load). I really can’t fault their approach as, IMO, many RV owners aren’t willing to make the effort needed to learn the proper inflation and to then maintain it.
We have had tire inflation stickers in cars for many decades and there have been massive vehicle recalls because their tires were underinflated – I have read that many were as much as 30% low. We don’t hear anyone making a case that the accidents and fatalities were the driver’s fault. That would be blaming the victim, which isn’t acceptable even if true.
OK, to your question. I am guessing your Cold Inflation Pressure (CIP) is in the 90 – 110 psi range so, IMO, +5 psi isn’t enough to avoid the pressure fluctuation that results in your overload. This is why I suggest a +10% value for inflation margin over the table minimum number.
In my Class-C RV, with LT225/75R16 LR-E tires, I am lucky as my RV is rather light. I really only need 60 psi F & R based on my “4 corner” scale readings. My certification sticker says 65 / 80 and my dealer delivered it at 64 psi all around.
For my application +10% would indicate 66 psi and a +15% margin > 69 psi. I run 70-75.
Even though I can be a bit “anal” about inflation, I also wrote THIS post and I really do not mess around with my tire inflation.
My TPMS is set to warn before I would be in overload, and I run across a scale once a year just to confirm I am not too far from my original “4 corner weights.”
In 2014 I drove Ohio > Oregon > Calgary > Yellowstone > Ohio over a seven-week period with temperatures ranging from the 90s to snow, and elevation of 20′ to 8,000′ and never had to adjust inflation.
Read more from Roger Marble on his blog at RVtiresafety.net.
##RVT816
Roger,
Like everyone else, I’ve struggled with this issue, and I have achieved some level of peace of mind with the following rationale:
With a 20% over-the-chart setting (for example, 75 instead of 60), my only risks are a slightly harsher ride, and possibly wearing out the center of my tires early.
BUT with an “on the setting” choice (60 exactly), I am in constant risk of overload (under-inflation).
With this perspective, my chosen tire pressure settings have become much less stress-inducing.