This week I bought the Airstream Safari a new set of tires. There wasn’t anything wrong with the old tires, other than being old. The tire industry makes various recommendations about replacing tires—I’ve heard anywhere from 4 years to 10 years, and the length of time seems to correlate with the confidence the manufacturer has in its product.
In this case the tires were Michelin LTX that we installed in January 2010, and although the tires were only used for five years and eight months, they were manufactured in late 2008 and early 2009. Tires begin to age from the day they are made, not the day they are installed, so I considered these to be nearly seven years old.
That didn’t bother me much, but on close inspection some fine “checking” (which is the tire industry term for cracking at the surface of the rubber) was apparent. Since my Airstream, livelihood, and family all depends on safe and reliable operation of these tires, it seemed like the time to swap in a new set.
In a way, the Michelins have been an experiment. Those of you who have read my blogs from 2005-2010 know that we historically had terrible results from using ST (Special Trailer) type tires on the Safari. After years of constantly replacing them because of on-the-road failures, I took the advice of Andy Thomson at Can-Am RV and installed the Michelin LTX instead.
As always, Andy was spot-on with his advice. We’ve never had a problem since. Those tires have traveled over 45,000 miles and the tread is still good. Not one tread separation or flat, whereas I was accustomed to dealing with a problem every few months when I was trying various brands of ST tires. In other words, the Michelin experiment was a success.
So it’s probably no surprise that I ordered up a fresh set of the same tires again (from Tire Rack). It was interesting to note that Michelin has re-designated them. Before they were Michelin LTX M/S LT235/75R15 104/101R. That decodes as follows:
- M/S =mud and snow
- LT = Light Truck
- 235/75 R15 = the size of the tire. My Airstream came with a Goodyear 225/75, so the Michelins are just a little wider. R15 means they go on a 15″ wheel.
- 104/101 R is their weight carrying capacity. In this case, they had two designations. 104 decodes as 1,985 lbs of weight per tire, which means all four had a capacity of 7,940 lbs. That’s a few hundred pounds more than our Airstream typically weighs when loaded. (The “101R” adds a caveat. If you want the tire to go up to 106 MPH, don’t exceed 1,819 lbs per tire.)
The new tires are Michelin LTX M/S 2 P235/75R15 108T. For whatever reason, Michelin is now calling them passenger tires (that’s what the “P” means) and giving them a higher load rating of 2,183 lbs per tire. But that’s really misleading. The industry says that if you want to use them on a truck or trailer you should divide by 1.1, which brings the load rating right back to 1,985. (Isn’t it fun, all the secret codes and hidden rules they have? No wonder people get confused.)
The speed rating went up too: “108T” means now we can theoretically tow at 118 MPH, as long as we keep under 2,208 lbs per tire. Sounds like fun.
I don’t hesitate to recommend these tires to my friends who ask for advice, because I’ve had this very good experience. But if you are happy using some other tire and having no problems, I don’t see a need to switch. Our 1968 Caravel does very well on ST tires, probably because it covers relatively few miles and is a much lighter trailer.
Now, having said all this, I’ve exposed myself to a small controversy. Some people like to debate this subject—and many others, such as tow vehicle choice—and undoubtedly one of them will either get in touch with me to inform me of my poor choice or open a thread on an online forum somewhere to discuss it. I have been intrigued to study the reasons why this continues to happen.
It’s perhaps oversimplifying, but I see two basic groups in every perennial online towing debate.
On one side you have what I’ll call the Rationalists. They look at the numbers and the guidelines. If, for example, the industry says that ST tires are engineered specifically for the needs of travel trailers, with reinforced sidewalls and special tread designs, that’s what the Rationalists will go by. After all, that’s what the experts say—and who are we to second-guess the engineers and the RV industry? They are the ones who made the things! Using LT or P tires is a sort of “off label use,” which might open you up to liability if something bad happens. And finally (say the Rationalists) just because those tires work for a few people doesn’t mean they’re a good idea.
On the other side you have the Empiricists. They look at actual experience, and argue that it has more value. If hundreds or even thousands of people are using LT or P-designated tires with a much higher success rate than the ST tires, who cares what the industry claims? Clearly their claims have been disproved by reality. This brings into question the industry motivations for steering us toward an inferior product (perhaps it was because the RV industry loves a low price? or perhaps to maximize profits?), which leads to deeper suspicion of industry guidelines.
Usually, both the Rationalists and the Empiricists firmly believe they are right, and they’ll often defend their position to the point of spoiling a party. (I used tires as an example, but the real fireworks get started over tow vehicle choice.) The problem is that neither side really has all the data.
The Rationalists don’t really know if the information they have received is correct. They’re just trusting what they see as the most authoritative source, and as we know, seemingly-authoritative sources can be dead wrong, biased by economic considerations, or distorted. The Empiricist can’t prove the validity of experience without a statistically valid survey. They’re just trusting what they’ve learned anecdotally. Neither side can definitively disprove the claims of the other, so the debate never ends.
Both sides will occasionally invoke the mythological concept of “common sense”. There is no common sense related to complex decisions like tow vehicles or tires. You might think that over time, a consensus would emerge from the Internet based on an averaging of real-world experience, but it’s no more reliable than standing in the middle of a stadium and asking everyone to tell you which football team is best.
Another favorite argument is the “laws of physics”. Nobody ever explains which laws of physics (Newton, Bernoulli, Avogadro?) they are invoking. Since there are many physical laws and the dynamics of towed vehicles involve many of them at the same time, I suspect that really the claimants are speaking of an imaginary law that says everyone must agree with them.
Since nobody knows everything, it’s easy for one side to introduce doubt into the other side’s argument, by suggesting possible (and unprovable) reasons why their position has a fatal flaw. Often this takes the form of suggesting a hidden liability or potential negative outcome that has been rumored. This puts your opponent on the defensive, but beware, because both sides can play this game.
Copernicus believed the sun was the center of the universe, altering a 2,000 year-old belief stemming from the ancient Greeks that the Earth was the center. Turns out everyone was wrong, and they were the smartest people on the planet at the time.
So my advice to people who get all worked up in debates about tow vehicles, tires, catalytic heaters, running the propane while towing, and other similar subjects is simple: remember why you got into Airstreaming. I’m guessing it wasn’t so you could argue with other people.
Anyway, you’re probably both wrong. Go camping and forget about it!