When a consumer has the luck to get a new trailer without some sort of tire damage, the ST game begins.
Consumers new to ST tires will make a lot of mistakes trying to properly maintain them. It’s much more complicated than maintaining tires on an automotive product. Although RV trailer tires and automotive tires conform to the same standards, there are major differences. Those differences are argued constantly in RV trailer forums. The first difference causes the most problems resulting in early ST tire failures, some catastrophic. RV trailer tires are not required to have load capacity reserves. All automotive tires must provide a percentage of load capacity reserves. Throughout the RV trailer industry its common knowledge that RV trailer axles are notoriously unbalanced. It can be an entire axle load imbalance or a single tire position imbalance. With tires providing zero load capacity reserves those imbalanced tires have a very high probability of failing and failing very early. I’m going to add a picture of a Keystone trailer’s certification label that depicts its GAWRs being set (by Keystone) at 5080# so the tires shown on that certification label can be used. Those tires provide – do the math - 2540# of load capacity at the PSI value, also shown on the certification label. The probability of having at least one tire severely overloaded on that trailer is very high.
Basically, the speed rating is telling us the tire can carry its maximum load capacity depicted on its sidewall. As the speed is increased beyond the speed rating the tire will overheat and start to degrade. Each time it degrades it’s added to the previous degrade. We had zero load capacity reserves and the degrading is eating away at the tires maximum load capacity. Something has to give.
A few years ago our government (USA) threatened most of the off shore manufacturers with increased tariffs if they did not mold a speed rating or speed letter to the tire sidewall. Although the load index system is not the official load indicator for LT & ST tires the load index system is used to display tire speed letters. (There is no letter for 65 MPH). The agency tasked with the responsibility of insuring that speed rating/letter is on the tire is US Customs. The only ST tire I know of that does not have a speed rating is Maxxis. According to TRA, an unmarked tire defaults to 65 MPH, no excuses allowed.
The regulation/standard allowing minimum tire load capacity equal to the GAWR has not changed. However, a few years ago (2017) RVIA, a large private membership organization mandated that all participating members (about 98% of all RV trailer builders) provide Original Equipment tires with the ability to provide at least 10% in load capacity reserves above the vehicle certified GAWRs. That RVIA recommendation will de facto effect all replacement tires recommended load capacities. That’s because of the industry wide standards that require all replacement tires to have a load capacity equal to or greater than what the OE tires provided.
