RV Tire Safety: LT versus ST tires for RV trailers

10

with RV tire expert Roger Marble

It’s no longer 1970 with a national 55 mph speed limit and with ST tires being introduced, i.e., “pushed,” by a large tire company as an alternative to the real LT truck tires of the day. I have been told that one of the “selling points” for this then-new type of tire was that “no one would ever pull their 15′ trailer faster than 55 with their bumper hitch.”

Well, times have changed. We now have “1-ton” diesel pickups that can pull a 35′ trailer up the side of a mountain and run 75+ mph all day long. Trailers now come with two bathrooms, residential refrigerators, two AC units, multiple TVs and other heavy equipment that we never considered possible in 1975.

What hasn’t changed is the fundamental science that a tire’s load capacity is still basically “Load = Air Volume x Air Pressure.” In fact, the actual load formula still used for current ST-type tires is identical to the one used in 1970 with the 65 mph speed limit still in the industry standards.

I can find no mention of alternate materials delivering increased load capacity in those standards. Yes, materials have improved and radials are better than bias tires, but basically the only benefits all these “improvements” delivered is longer life and better fuel economy and tread wear. Some construction features such as the addition of nylon cap strips or full cap ply have allowed an increased resistance to the heat from higher speeds, but I haven’t seen any increase in load capacity in either passenger or L- type tires over the past 40+ years.

As I have posted in this blog, “There is no free lunch.” If there is, why haven’t tire companies increased the load capacity of passenger and LT-type tires if all these “improvements” are available to tire engineers?

What “feature” is in ST-type tires that gives them the +10% to +20% more load capacity over an LT tire of the same physical size?

IMO there is no reason why RVs could not be supplied with LT tires other than it would increase the cost of the tires to the RV company.

Remember, it is the RV company that is responsible for selecting the tires they provide. We all see numerous posts from some who are running truck 17.5 size or LT 16″ tires with improved durability, so I see no reason to believe that the entire market could not benefit from a switch from ST- to LT-type tires.

One thing is that the LT tires that have to meet the new DOT standards (FMVSS 139) that were introduced in 2002 are probably more durable than the ST tires that are still only required to meet the standards of the 1970s.

I am not saying that some of the newer ST tires with newer construction are not significantly better than the same size tires from the ’90s, but IMO there is still a limit.

 

Read more from Roger Marble on his blog at RVtiresafety.net or on RVtravel.com.

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Randy Shrimplin
7 months ago

I ran Michelin LT’s on my 4 horse trailer after a blow out on my crappy OEM Load Stars. Never had another issue and it rode much better. They also were still on the trailer 40K miles later when I sold it.
I also run car tires on my boat trailer because it ride so much better and I dont worry about blow outs.
Bottom Line: Weigh your rig.
Choose a tire that’s load rating exceeds 1/2 the axle weight.

Alain Tasse
8 months ago

Now, I am VERY confused. For years, everyone in the rv business, its commentators, its experts and other bloger forum’s so-called experts “having used this or that for soooo many years without any problems”, etc, had me convinced in believing all the hullabalu about the ST tire’s sidewalls being much better, much stiffer and much more resistant to the particular type of flexing that occurs when driving, turning and parking travel trailers or fifth wheels than LTs. After the appearance of the “china-bombs syndrome” a few years ago, people started to realize that practically all ST tires were manufactured in China anyway, whatever the
“US brand name” stamped on them, leaving the consumer with very few, if any, alternatives.

Now, coïncidentelly, we hear that LT tires are “just the thing” for trailering.

It also appears that a handfull of rv manufacturers, like Jayco, have seemingly struck a deal with Goodyear, who now has resumed manufacturing ST tires in North America, to equip their new trailers with “US-made ST tires”. I guess their ST tire prices have dropped again enough to catch the big manufacturer’s attention and make it worth their while.

So I guess the real question should now be, are US-made Goodyear ST tires better, worst or equal quality than their US-made Goodyear LT tires, or why even bother to engineer ST tires at all? We shall see, in time, who wins between; Beta or Vhs, Plasma or Lcd, Android or Apple, etc, etc, etc.

Roger Marble
8 months ago
Reply to  Alain Tasse

Alain, The biggest issue is I know of no way to do a direct comparison of ST vs LT tires other than an expensive tire test. We can’t depend on the DOT test results, which in all probability the tires all pass, simply because the RV industry and ST tire mfg companies were successful in getting St tires excluded from the significant improvement in testing with updated standards in 2002. There is no question, in my mind, that the tests for ST type tires are easier to pass than the tests for Passenger and LT type tires.
I have looked at the construction of a GY Endurance and it certainly looks better. Now remember I do not have access to the actual specification or material properties used by GY but in the Endurance tire line, they appear to have added a Nylon cap over the steel belts. You can confirm this by reading the material list molded on a tire sidewall.
“Quality” is a tough call when you have two different specifications to start with. Is Quality just a measure of a tire’s ability to meet the specification for that product?

You can think of it this way. If I had two pieces of chain. One rated at 500# and another rated at 550#. They both meet a strength test of supporting the rated load and if you tested 100 pieces of each and found that all 100 passes the rates strength test how would you rate the ‘Quality”? You can’t say the 550# chain is better quality than the 500# chain as they have two different goals, just as you can’t say a 1-ton truck is better quality than a 1/2 ton truck because the 1-tone can handle more load.

Your example of Beta vs VHS is a good example of the confusion possible. Beta was judged technically superior to VHS but Sony made a marketing decision to prevent other companies from using the Beta specification in their video players. The result was that VHS units were less expensive so many people bought on price. Eventually, Sony lost out. Not because the “Quality” of that video format wasn’t as good as VHS but because the market was “price-sensitive” and too many people selected lower cost over better quality.

Kevin
8 months ago

We are migrating to LT tires. 2 down and two to go. The ST tires seemed to last about 15,000 miles before failure. I monitored tire pressure daily. I read (and just verified) that Airstream Trailers are now using LT tires as OEM. I sense change in the air and ST tires but be declared as “dinosaurs and disappear in a few years.

CTK
7 months ago
Reply to  Kevin

I gave up on ST years ago – too many shredders. Thus, haven’t had a shredder in years.

Andre
8 months ago

The reason you cite–cost–is the reason it will not happen in my opinion. If a rig would sell for $17,000 with ST. tires, then maybe it’s $17,500 with LT tires of similar capacity. If the rig would sell at $17,500, the manufacturer would rather sell it at that price with ST tires on it and pocket the difference. I don’t think most people make a trailer buying decision on what kind of tires it comes with. A salesperson will say, “You can always change those out…” I find that typical trailers are built with such compromises throughout. They could have a waterless P trap in all sinks, but that slight extra cost multiplied by many thousands of trailers is significant to the manufacturer, but since the consumer doesn’t demand those things they don’t get put in, whereas people demand things like giant slide-outs and will pay for those features. The market tends to settle things out in terms of price, and manufacturers are quite conscious of the price vs profit vs. features balance.

peterb
8 months ago

I’ve been using LT tires for years, never have a problem. Always had problems with ST tire and not because of low tire pressure.

Gene
8 months ago

OK, color me confused! I have always gotten the impression that ST tires and not LT tires are what I should be running on my RV. After reading this article now I’m not sure. Are you suggesting that all things being equal, LT tires of the same size, load rating, etc are better to run on my RV? I don’t mind the cost, just want to put best possible tire on my RV. Thanks for keeping us informed.

Greg Bryant
8 months ago
Reply to  Gene

That seems to me what he’s saying. If it is, it will make my next tire buying chore much simpler and convenient for my RV.

Roger Marble
8 months ago
Reply to  Gene

Gene, The problem is that “all things are not equal” as there are no LT tires of the same size, load range, and load rating, etc as an ST tire. There is always something that is different.
Sometimes the only option would be to go with larger size LT tires but in some cases, there is no physical room to run the available larger size tires.

IMO, what you “should” be running are tires built to the latest industry test standards (LT) that can offer at least 15 to 25% “Reserve Load ” capacity