Quote:
Originally Posted by Cummins12V98
Can't use your own words to explain I guess or answer my question.
PLEASE tell my why every tire out there has a Weight/Inflation chart and you don't think it should be used.
I am guessing you work for some sort of Government Agency?
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Weight inflation charts were developed for the tire industry. They are standardized by the Tire and Rim Association (TRA). They are very useful for Original Equipment (OE) installers to speed-up production. They are not recommendations. They are precise inflation pressures divided in increments. They are necessary for aftermarket installers of plus sized tires and for determining inflation pressures when changing from “P” tires to “LT” tires.
They are probably most useful for consumers that increase a OE designated size to a higher load range.
It’s the industry misinformation that gets consumers confused. I cannot be wishy-washy with my tire presentations and that’s why I write strictly from industry regulations (NHTSA & FMVSS) and standards (USTMA).
Probably to get a better understanding of initial tire inflation pressures one should become familiar how and why the vehicle manufacturers determined and set OE tire inflation pressures. It’s quite simple, they MUST install OE tires that, at the vary minimum, provide – via inflation – a load capacity that will support the vehicle’s certified GAWRs. For automotive fitments GAWRs will provide the necessary vehicle load capacity reserves. For RV trailers there is no requirement for tire load capacity reserves. This is very important; vehicle manufacturers have the sole responsibility for setting OE tire recommended cold inflation pressures. Because the direction to do so is written in the FMVSS standards, those set inflation pressures become the minimum standard for that vehicle. Why? FMVSS standards are written to insure minimum standards are enforced by the manufacturing industry. It may be best understood when you read the basics for replacement tires: Replacement tires MUST provide a load capacity equal to or greater than what the OE tires provided.
The vast majority of RV trailer axles are overloaded on one end or the other. Only scaled weights can be used to manage the weight across their axles. As many have found, guessing at the proper weight for trailer tires can be very costly. At the minimum, follow the vehicle manufacturer’s minimums.
A lengthy post getting longer: the following quote is from the USTMA RV tire instruction manual. It encompasses both Motorized RVs and RV trailers.
“Inflation pressure recommendations may also be determined based on the tire manufacturer’s specifications, which define the amount of inflation pressure necessary to carry a given load. These inflation pressures may differ from those found on the vehicle tire placard or certification label. However, never use inflation pressures 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.”