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Friday, October 20, 2017

Will confusion on how much inflation be resolved?

Hi Roger.

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 FMVSS Regulations 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* morning @ 1100' altitude. When traveling, I had a morning @ 5000' and temp in the upper 30's. This produced a pressure of 1-2 psi below the minimum. I was going to be traveling into a warmer climate (95*), 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.

Not sure if there ever will be a resolution to the Inflate to the placard vs Inflate to the actual tire load. I would liken this to the change oil every 3,000 miles vs 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 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 CIP is in the 90 - 110 psi range so IMO +5psi 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 > OR > Calgary > Yellowstone >OH over a seven-week period with temperatures ranging from 90's to snow and elevation of 20' to 8,000' and never had to adjust inflation.

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