RV Tire Safety: LT versus ST tires for RV trailers

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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.

 ##RVT931

 

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Randy Shrimplin

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

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.

Kevin

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.

Andre

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

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

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.