Originally Posted by Airdale
I know you must know this; Vehicle manufacturers are the only ones authorized to select and fit OE tires. Once selected they are described on the vehicle's federal certification label, tire placard and in the owner's manual.
With few exceptions ST tires and LT tires are not manufactured in the same sizes. When they are, the load capacity of the ST tire is far greater than the LT tire.
To compound the difficulty of doing things right many of the major LT tire manufacturers have worded their warranty packages with statements that disallow ST tires as replacements for LT tires. Michelin has a statement in their warranty package that disallows using replacement tires that conflict with safety warnings in your vehicle's owner's manual. Most RV trailer manufacturers using ST tires as OE without designating options will only recommend ST tires as replacements.
Misapplication is a key word. What does it mean? I've asked a number of knowledgeable people with reference to ST and LT tires. The common answer is based on the vehicle manufacturer's selection for OE tires. It seems that because the LT tires is not specifically designed for service on trailer axles it is a misapplication to use them to replace the ST tire which is specifically designed for trailer axle service.
The FMVSS are not binding on the public at large but very binding for the vehicle manufacturer. In 571.120 the manufacturer is directed to select tires with a minimum load capacities equal to the vehicle's certified GAWR. But, the wording also leaves room for other considerations and uses the phrase "appropriate for that fitting" and go on to also instruct the vehicle manufacturer to set the recommended cold tire inflation pressures for the OE tires. When we take the inflation pressures to the load inflation chart for the OE tires we find the minimum load capacity as set by the vehicle manufacturer as per FMVSS regulations.
Every RV trailer owner's manual I have read (and I read a lot of them at RV shows) only recommends replacement tires of the same size and load capacity be used. Or, others recommended by the vehicle manufacturer.
Every approved tire plus sizing procedure I've read tells the installer - in part - to check the tire placard to insure the replacement tires have the load capacity to equal or exceed the OE tires. Will this sometimes allow the use of LT tires? I used to think so until all the new warranty packages started using wording to disallow that possibility. Are LT hybrid tires suitable for trailer service. That's what their manufacturer says so it must be so. But, there are few of them.
Yes I do understand what you are saying and I know about the vehicle manufacturers responsibilities.
What I don't understand is how RV companies can claim the tires they select are the only ones appropriate for use on the RV given that they are not willing to stand behind their choice and offer a meaningful warranty on the tires they have selected. Can you provide a list of RV companies that offer multi-year warranties on these special tires that were so carefully selected by the RV company?
IMO the "misapplication" is not much more than a back door escape clause to be used when a company does not want to stand behind their product or when they can point to the fact that the change from OE size resulted in a decrease in load capacity or lower speed capabilities or perhaps the use of a highway tire in off-road application or summer tire in winter driving.
Could you provide links to warranty literature that says that the use of an LT tire in any
application where an LT was not the OE application would void the warranty?
Given your apparent position, I trust that you would consider it a misapplication if an owner wanted to use LT type tires on small pick-up trucks that were delivered with passenger type tires. Maybe you could ask one of those knowledgeable people to contact me so they can educate me as to the design features in an LT tire that would make it deficient for application on a trailer or make it somehow deficient if ever used on a small pick-up that was delivered with passenger type tires.
The concept that an LT type tire that exceeds both the load capacity and speed rating and warranty time of the ST tire it was replacing is somehow deficient seems like a long stretch considering the fact that the RV company can not demonstrate having done any technical evaluation for the selection of tires for use on the RV other than meeting the needed load capacity published in some letter of booklet.
I have never heard the term "LT Hybred" before. It is not recognized in US Tire & Rim Association spec book. Where can I learn about this new type of tire?
The strict rule that only the replacement of the OE tire with an exact replacement creates significant problems for a few trailer owners. I have identified a few applications when the tire selected and provided by the RV company does not follow the published load and inflation tables and in fact is only allowed because that specific tire importer submitted a letter to NHTSA claiming that the tire was capable of carrying the load that would allow the tires to meet the load capacity requirements in federal regulations. I got this information directly from NHTSA when questioning how it was legal for a tire to be supplied when the load capacity molded on the tire did not meet the GAWR. Nowhere in the literature from the RV company was the manufacturer of that brand tire identified as the only acceptable replacements.
As a side note. In all that RV literature that you read have you ever seen a mention of the max speed rating of the tires the RV company has selected as appropriate? I would think that this is an important bit of information for them to provide the prospective owner of the RV.