When it comes time to replace the tires on your RV trailer you may have limited options. Sometimes you may also be confronted with a limited supply problem that depends on your selection. What can you do? What are some options?
Now, I am assuming you have followed the general instructions to get your RV on a truck scale when fully loaded to the heaviest you ever expect to be. As a minimum you should have confirmed the load on each axle when the trailer is loaded to its heaviest. I have numerous posts in my blog RVTiresafety.net and on RVtravel.com on scale weights and how to calculate and estimate the load on the heaviest individual tire.
So, knowing you need a tire that can support at least 115% (125% is better) of your measured or calculated heaviest load, you are ready to start shopping.
Sidewall shear
I had one reader express some concern about what he called “sidewall shear” forces and thought a stiff sidewall would be a better selection. I have no idea how he was going to measure the inflated sidewall stiffness and pointed out that uninflated sidewall stiffness was not a reliable predictor of the inflated stiffness.
Here is what I told him:
I would not worry about “sidewall shear,” as the real culprit for belt forces is interply shear at the steel belt edges which can lead to a belt separation.
Sidewall failures, which some confuse with “blowout,” is the result of running at highway speeds with significant (40% to 60% or more) air pressure loss.
These posts cover most of the the forces that cause belt interply shear. Don’t be misled and think it’s the sidewalls that are being overloaded. It’s not.
Tire pressure monitoring system
You can get warned about the sidewall run low flex with the use of a tire pressure monitoring system (TPMS) that is properly programmed to alarm as soon as air pressure drops below the level needed to support the measured load on your tires. This comes from truck scale weight measurement and consultation of tire load and inflation tables mentioned here.
Belt separations develop over hundreds to thousands of miles. A TPMS will not warn of impending belt separation BUT sometimes it is possible to “see” indications of possible impending or probable belt separation with a close visual inspection to check for run-out, either radial or lateral. I posted a link to a video on a “Free Spin” inspection in this post.
The Goodyear Endurance tires I have inspected included a belt cap in addition to the two steel belts. I suggest you read the material list that is on all tire sidewalls. If there is no mention of material over the top of the two steel belts in the tread, then I would suggest you keep looking.
If you find an LT-type (light truck) tire that can support 115% or better of the scale load on your heaviest tire, that might be an acceptable alternative if it also has a nylon or Aramid cap belt. LT tires have to pass more difficult DOT testing than ST-type (special trailer) tires, so that should give us some additional confidence if we choose to use those tires in RV applications.
Maximum operating speed
Finally, you need to limit your MAX operating speed to 75 mph with LT-type tires and to 65 with ST-type tires. Even though some ST-type tires have a “Speed Symbol” letter that implies speeds higher than 65, we need to remember that the test for those speeds is only 30 minutes. In reality the Speed Symbol is really just an indication of high heat resistance. The load capacity of ST-type tires is based on a formula that specified 65 mph as the max operational speed when the ST type tires were first introduced.
Side comment and thought on load ratings. If you have two tires of the same size and load range, why would any tire company suggest that one tire could support significantly greater load without there being some durability trade-off?
Roger Marble
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If you have tire questions, check out Roger’s Blog as well as his posts on RVtravel.com. There are hundreds of posts covering everything to do with tires.
If you still have a question for Roger after searching the above posts, send your inquiries to him using the form below.
MORE POSTS FROM ROGER
- RV Tire Types 101: Selecting the correct tire for your RV or other vehicle
- How close to ‘Max Load’ is OK for RV tire inflation?
- What is the proper inflation for my tow vehicle and RV trailer tires?
- How fast can you drive safely on ST-type tires?
- A quick note on tire “MAX PSI”
##RVT1203
In 50+ years of RVing I’ve run a lot of different tires. On my 40′ 5th wheel I have Goodyear Endurance tires and I’m really happy with them.
Same here.
I replaced the Trailer Kings on my TT within the first year with GY Endurance. I wanted a tire made in the US. My tire shop told me all trailer tires were imported until they came in and he saw Made In USA on the tire. He also said the sidewalls were much stiffer.
I could feel the difference as soon as I hit the highway.
I also had them balance the tires. He said they don’t usually balance trailer tires.
Thank you, Roger, for another informed, educational, and patient discussion of RV tires. Have a great day and safe travels!