Originally Posted by Tireman9
To all those that run into tire dealers that refuse to mount LT type tires on trailers have you asked to see any company documentation that supports this position? Also has anyone asked how do they plan to handle tires on trailers that were delivered with LT type tires?
Yes there are things that must be taken into account when considering changing from ST to LT type tires.
To those dealers I would also ask if they refuse to change tire size on a passenger car and do they refuse to apply tires with lower Load Index or Speed rating than came OE on the car?
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.