It's amazing to me that so many people recommend inflating tires to the maximum pressure noted on the sidewall. Lots of folks on discussion boards, most tire salesmen, and apparently many RV manufacturers all say to do this. I think that since most tire failures seem to be caused by under-inflation, they are simply trying to cover their butts and not bother with taking the time to give any accurate advise. That is, those few who really know anything about it. (Of course if a tire develops a leak it's going to be under inflated, but that doesn't mean everyone should OVER-inflate tires.)
The ONLY people who know about proper inflation for any particular tire are the tire manufacturers. In my experience, every tire manufacturer I've looked up has a web site where they publish inflation tables for particular models and sizes of their tires. You find the weight that the tire will be carrying and the chart will show the appropriate pressure to use. Yes, there is a maximum pressure rating, and if you try to load the tire higher than it shows the tire is capable of by increasing the pressure above that maximum, you are asking for tire failure.
There is a reason we use pneumatic tires on vehicles instead of rigid ones. For a cushioned ride. Old tractors once had steel rims and lugs, but they operated on soft dirt and didn't worry about shaking their machinery to pieces. Common sense tells you that the higher the pressure in the tires, the less cushioning there will be for the load. If you run a tire at 80 psi when it only needs 40 psi, you should pretty much expect to see your trailer disintegrate over time. On a halfway rough road, that time could be pretty short.
Even publications like Trailer Life often publish letters from readers who claim that all their "experts" told them to just use the maximum pressure noted on the sidewall. In the current issue (Sept 2018) of that magazine, though, I finally see one response from the editors that makes sense. They say, in part, "Check the tire manufacturer's load and inflation tables for the tires. It's possible you may not need the full 80 PSI on the tire sidewall. Lowering the pressure somewhat, still allowing a reasonable weight safety margin, means the tires will be a bit more flexible and save some wear and tear on the trailer and its contents. A "safety margin" means if you need 65 PSI per the tables to carry the weight at each tire, go up by 5 PSI to add some margin of safety. This is not a hard and fast figure ..."
Here's what I did when I bought my 1999 22 foot Hi-Lo Classic three years ago. Knowing the tires were original to the trailer and thus a minimum of 16 years old, I replaced them all including the spare (they had lots of tread but were showing some little sidewall cracks, and bigger cracks in the bottom of the tread grooves). I did a lot of research online, and read sad tales from users of a lot of different brands, but saw no such stories about Maxxus tires, so that's what I bought. I upgraded from the original C range tires to D range. I looked at the Maxxis inflation tables and the recommended PSI for the load I was going to put on those tires was only about 32 PSI! (The maximum pressure rating on the sidewalls was 80 PSI.) I added about 6 to 8 PSI for a safety margin, even knowing the Hi-Lo would have a little stiffer ride. And driving on an old concrete road with noticeable bumps at the joints in the pavement for about 20 miles shook my lower trailer door apart and I had to rebuild it. I can't imagine what would have happened if I had used 80 PSI. Maybe all the upper cabinets would have fallen down ...
Also, I use a little common sense when driving. Can there be a reason the manufacturers of all trailer tires (I'm told) say the maximum speed rating is 65 mph? And yet I see these morons pulling a trailer the maximum speed limit on the freeway, which is 80 here in Idaho. Or 85, because they think the state police will let them get away with 5 mph over the limit. For four hours across the desert in southern Idaho when the air temperature is 97 degrees; goodness knows what it is on the black asphalt.
I drive at 65 or below on the freeway. I bought a Hi-Lo largely to get good mileage, and the high speeds do a lot to eliminate that advantage. Hey, you are on vacation, right? What's the hurry? Driving at 75 instead of 65 for an hour doesn't save you 10 minutes ...
About Goodyear. My original trailer tires were Goodyear Marathons, made in the USA, which had a good reputation. Then they switched to China production and the result was all the horror stories you find on the Internet about Marathons blowing apart and tearing up RVs. The trailer manufacturers kept using them because of the good rep. When that went away, Goodyear finally came out recently with a new trailer tire that they say is made in USA and is a big improvement. They say. But sorry, Goodyear, I just don't trust you any more.
I hope this at least makes people think a little about tire pressures in a way that makes sense.
Roger
