RV Tire Safety: Attention to detail is VERY important when it comes to tire size

I got a question from Lee H. on the Facebook page “RV Tire News, Information”. The information provides an opportunity to show why the details of tire “size” can be critical to making the selection of what tires you need. This example is for a large Class A, but the details can just as easily apply to a 18′ bumper pull on 14″ tires.

Roger, I have a question on load balance and proper inflation. Our 38′ Diesel has 275/80R 22.5 Load Range H Michelin tires. The GAWR front is 12,000 lbs. and GAWR rear is 20,000 lbs. The 4 corner weights are LF 5,300 lbs., RF 6,350, LR 9,950, and RR 10,000. I’m within range on the totals on both axles, and within tire load capacities at all positions.

However, look at the 1,050 lb. DIFFERENCE between the LF and RF tires! Based on the weight carried by the RF tire, I’m running 110 psi in all 6 tires.

Roger, if you happen to read this, I would be interested to know if I could safely run 90-95 psi in the rear tires, or should I continue to gear the inflation of all 6 to that RF tire number? I’m a little uneasy about keeping 110 psi in the front and 90 psi in the rear. Maybe that’s no problem. Please tell me.

I will say I’ve driven the coach for 20 years with 110 psi in all 6 tires with no problems. And before anyone suggests I start moving things around in the basement or in the coach, we’ve always, based on that weight, verified early in 2005 and then weighed again in March 2024, loaded our heaviest items on the left side of the coach. My theory is that the kitchen, with all appliances including a dishwasher and washer/dryer, were placed in the right side of the coach, which seems like a bad idea. I can’t move those.

Let the suggestions commence! —Lee H.

My reply

Lee,

A Michelin LR-H XZE (NOT the LR-G XZE2) 275/80R22.5 requires a MINIMUM of 105 psi if loaded up to 6,435 lbs. single. If loaded up to 10,030 lbs. in dual, you need a MINIMUM of 85 PSI.

Since you have LR-H and NOT the LR-G XZE2, you are OK. BUT I would suggest you run 115 psi in the fronts and 95 psi in the rears to give yourself a bit extra load capacity margin. The front-to-rear inflation difference is OK.

Necessary to pay attention to details regarding tires

FYI, I will be using your question in my article in this week’s RV Travel newsletter, as it provides a good example of the need to pay attention to the details of using the COMPLETE size, type and load range description. It would be easy for someone to just look at the numbers “275/80R22.5” and use the inflation for the LR-H tires while running LR-G tires. If someone did that, they would be overloading the tires and might suffer one or more failures.

NOTE: When it comes time to get new tires, you might be forced to select Michelin. I don’t know if other brand tires have different load capacities in the different load range tires.

Here is the Load / Inflation chart for the subject tire.

Please note that Michelin has different load capacities FOR THE SAME “SIZE” tire but different load range. This is an excellent example of why you need to provide the “complete” tire description when talking about tires. This includes the letters and numbers in the “size” and ALSO the load range. If you take a quick look at other questions and posts about tires you will see that very few include all the important nomenclature.

Roger Marble

Check out my Blog www.RVTireSafety.Net

Read more from Roger Marble on RVtravel.com.

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