New ST Goodyear tires

CALandLIN wrote:
Those that read my posts here and on other forums under more than 6 user names may be kind enough to admit that my posts revolve around approved regulations and tire industry standards. That’s where all this information is going to come from.

Trailer tire recommended inflation pressures are different from automotive recommended inflation pressures. A quick check of your automotive tire placard will prove that, because those recommended inflation pressures are always providing a percentage of load capacity reserves.

Vehicle manufacturer recommended inflation pressures for RV trailers provide little, if any, load capacity reserves. Therefore, for may years the norm has been to insure they are inflated to the maximum amount listed for maximum load capacity. And, almost all certified RV trailer tire recommended cold inflation pressures do match the maximum inflation pressures on their sidewalls for maximum load capacity. Therein lies the first obstacle. NHTSA & the USTMA both agree that the recommended cold inflation pressures found on the vehicle certification label are the correct and minimum pressures to be used. Here is an excerpt from the USTMA PDF; “Never use inflation pressure lower than specified by the vehicle tire placard, certification label or owner’s manual. Nor should inflation pressure exceed the maximum pressure molded on the tire sidewall.”

We may all see a change in the size and load capacity of our Original Equipment tires. RVIA has made a strong recommendation for all RV trailer tires to have a minimum 10% load capacity reserve above the trailer’s certified GAWRs. Will it change the way the recommended cold inflation pressures are applied to the certification label by the vehicle manufacturer? (?).

A tire designation (ST235/80R16) may have more than one load capacity. However, all load ranges within that size designation will be compatible with the same load & inflation chart. That means that, that tire, at LRG will still provide the same load capacity as the LRE when inflated to 80 PSI.

IMO, when inflating trailer tires, any design, to the load carried is mentioned, cringe, and then, if possible add inflation that provides at least 10% in load capacity reserves.

USTMA plus sizing standards. First, does the vehicle manufacturer approve the upgrade? Will vehicle safety be compromised in any way by such an upgrade? Will the upgrade fit in the wheel well without being obstructed in any way. Is there sufficient distances between the axles - when applicable - to insure the tires do not strike each other. Will new wheels be needed to compliment the new tire size, load capacity and maybe wheel pressure constraints.

Plus sized tires must have the capability to provide a load capacity equal to or greater than what the OE tires provided. The new terminology for tire size is Size Designation, and it includes the prefix. The prefix is the primary tire design indicator. I’m going to leave that one right there. It is not clear to many people how important vehicle certification is to the industry as a whole.

Plus sizing is one of the primary purposes for standardized tire inflation charts. For instance, if you were to have ST225/75R15 LRE tires as OE on your trailer and decided to plus size them with ST235/80R16 LRE tires you would have to change wheels. Because the two sizes use completely different load inflation charts a new recommended cold inflation pressure would have to be set by the tire installer. The vehicle certification label would no longed be valid. NHTSA has foreseen that problem and allows the use of an auxiliary tire placard. The tire installer would use the auxiliary placard to display the new tire & wheel sizes and a new recommended cold inflation pressure for the plus sized tires. Notations should also be made in the vehicle owner manual. So what would be the new recommended cold inflation pressures be? The owner is, in all probability, searching for more load capacity reserves. Personally I’d insure mine had 15% above each GAWR. To match the new RVIA recommendation, 10% would be required.

To help validate your involvement with ST tires, why don't you tell the new people here about your personal experience with ST tires on your own trailers over the years and the number of failures that you have experienced?