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RV Tire Safety: Basic tire knowledge; and could you help this RVer?

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I monitor a number of RV forums and when I see someone asking about tires, I will make the effort to learn about the problem and offer possible solutions.

Recently there was a question on inflation for both the tow vehicle and the travel trailer. The comments seemed to be all over the place, so I decided there was a need for some basic foundation of information needed. Following is my reply and attempt to provide the basic information needed by RV owners.

Tow vehicles

Tow vehicle tire size, type, and inflation should go by the Certification Sticker on the driver door jamb. This was established by a team of tire and vehicle suspension engineers over a period of two to four years with numerous changes and tests run on different specifications and performance parameters that were fine-tuned to meet the goals of the vehicle design team. The sticker provides a recommended inflation that normally delivers 30% to 35% Reserve Load. So those numbers should be followed unless you have done a lot of research and understand the tradeoffs. Do not forget that few people in the tire store have technical training beyond how to sell tires, so I would be careful with the information they provide.

Travel trailers

Travel trailer tires for almost all RV trailers have a single spec, that being low cost. I have never heard of any vehicle testing or evaluation that compares different constructions or ratings for the application of a tire to the travel trailer.

To achieve low cost, tires are only required to meet a single requirement: They meet the minimum load capacity specification needed to support the RV. In 2017, the RV Industry Association (RVIA) established a Reserve Load of 10%. However, for RVs built before 2017 there was no Reserve Load requirement.

Those of you that have read the owner’s manual and reviewed the Certification Label information and the Load and Inflation information molded on the tire sidewall may have noted that for most RV applications, you can only achieve the tire’s 10% Reserve Load capacity when inflated to the level required for the maximum load capacity.

Yes, this basically means you must run the max inflation for the tire’s Load Range if you want to have the minimum margin of Reserve Load recommended by the RV Industry Association.

Related information

The words “Max Inflation” on the tire sidewall is NOT the highest inflation the tire can tolerate. It is the highest inflation that will provide the greatest load capacity of that tire. The published Load & Inflation tables show the direct relationship between inflation and load capacity. If you want to increase load capacity, you MUST increase the inflation. But once you reach the stated “Max Cold Inflation” there is no further increase in load capacity available for that tire, even if you increase the inflation above the number molded on the tire sidewall.

In the subject post there was some confusion about the Michelin “LTX” line. One poster thought this was some special “hybrid” type of tire so felt the need to clarify the tire “type” nomenclature.

Letters in tire size are important

The letters before the numbers in the tire size are critical and important, but too often people seem to ignore that important info. The P is for Passenger, LT is Light Truck, and ST is Special Trailer. ST should only be used on trailers and is not approved for use on passenger-carrying motor vehicles. If a P-type is applied to a trailer, its load capacity is to be reduced by dividing the load capacity stated on the tire or in the Load & Inflation tables by 1.10. But if an LT tire is applied to a trailer, no reduction in load capacity is required.

A few days later the following was added to the Forum thread:

“—————— Steer Axle — Drive Axle — Trailer
Weight #1 – Truck only/hitch/bars — 3180 3520 (exceeds 6500 GVWR)
Weight #2 – Truck and Trailer with WDH bars — 2980 4320 4880 “

Side note: The owner had previously stated the tow vehicle GVWR was 6500, so the initial scale reading seems to exceed his GVWR!

My response: I am assuming the “trailer” scale was for the 4 tires on the RV. If so, it sounds like the trailer was empty when you did the weighing.

Michelin

While waiting for a response I saw a comment about Michelin tires in this thread:

It was helpful to learn of both the Michelin “hybrid” LTX and the Cooper XL alternatives to LT tires although when I looked up the Michelin LTX I saw that it comes in A/T and A/S versions … even more confusion … Is the A/S the “hybrid” and the A/T the real LT??

My response: I’m not sure what you mean by “hybrid.” Michelin has a “line” of tires it calls “LTX.” This includes both passenger-type and LT-type tires.

Think of this: General Motors has a “line” of cars called Chevrolet with many types of vehicles from sedans to SUVs and pickups.

Basic “families” of consumer tires

In my post, I covered the three basic families of consumer tires: Passenger, Light Truck, and Special Trailer. Each “family” has many different sizes and many different tread patterns like the A/T, which is a traction tread pattern, and the A/S which is All Season and provides less off-road or snow traction.

Within each family, there are also different levels of Load Capacity.

P-type “family” tires come in “Standard Load,” that has no special markings, and also XL for Extra Load.

LT and ST “families” have greater load capacities, so they have letters assigned to the “Load Range” or LR, with the different LR having letters starting at C, D, E, and on up in some brands. Each letter has a specific maximum load capacity at a specific inflation. The load capacity is published in tables available in some owner’s manuals or tire data books, or even on the Internet as seen HERE.

If you have a tire size or Load Range not covered on that page, you can send me a direct email [tireman9 (at) gmail.com] and I will check my reference files for you.

All the above applies to tires made to U.S. Tire & Rim Association standards. Europe has some similar but different standards with different codes. So are tires made to the standards in Asia. I will not go into those standards as I probably have overloaded you with the above.

Clearly, the owner of the truck and trailer needs to learn more facts about tires and the proper loading of his tow vehicle truck.

I am wondering how many readers would be able to offer advice to this fellow RV owner.

Have a tire question? Ask Roger on his new 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 his blog at RVtiresafety.net or on RVtravel.com.

 ##RVT1079

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Bob p
19 days ago

I have a 23’ TT, the owners manual states tires should be inflated to 65psi cold. When I looked at the sidewall it says Maximum Pressure 65psi, it’s a 2020 model year so I guess the manufacturer didn’t allow 10% overload capacity. They are ST.

Joel
19 days ago

I can only offer my experience with my travel trailer. I use 8 ply and use maximum air pressure on my travel trailer. On the tires I use it usually runs between 60 & 65 pounds. This has worked well for me. I do this on the advice from a source, who just happens to be my brother. His experience was gained from the transportation manager of his school district which covered some 5000 miles daily in Wyoming. This considers the weight and the temperature of the tires at max pressure. I have had very good luck running tires this way. As stated in the article, the max cold pressure is listed on each tire. As for believing tire installers you must insist that they put the pressure in you require. I have had tires put on my tow vehicle and tt and every time I check they go with 32 lbs. check on your own to assure that they are filled to your requirements.

Roger Marble
19 days ago
Reply to  Joel

Joel, Yes your Load Range D tires have a stated max cold inflation of 65 on the sidewall and assuming the load on your tires when checked on a truck scale NEVER exceeds the stated Max Load you should be good to go with 65 PSI. I do hope your scale load reading is no greater than 90% of the max load number molded on the sidewall.

Also checking the pressure set by installers or at the service station is also a good idea. I think that some installers are working ‘on automatic” and inflate to some level their boss told them to do which may not be the inflation the customer requested be on the work order.

Wyoming is a beautiful country. I am planning to visit next August when FMCA holds another convention at Gillette where I will be giving seminars on tires in RV application.