By Roger Marble
I recently received a question on tire requirements involving “quality” and load capacity:
I have been under the impression that a certifying agency, American Tire and Rim(?), sets the standards in the U.S., and then all tires sold in the U.S. must be designed to those standards. So a cheap, unknown brand, load range D tire from Walmart would have the same load and inflation specifications as a Firestone tire from a Firestone dealer?
First, the Tire and Rim Association, Inc. (TRA), a private industry association, only lists dimensional standards and the Load/Inflation tables.
The U.S. Department of Transportation (DOT) has a department, the National Highway Traffic Safety Administration (NHTSA), that publishes tests and performance requirements. I would consider these to be one measure of “quality.”
All tires for highway use must pass NHTSA tests
All tires for highway use sold in the U.S. must be certified by the tire manufacturer to be able to pass NHTSA tests. The “DOT” symbol on a tire indicates that passed the NHTSA tests when it was first sold.
There is no agency or organization that runs checks on the tires sold, as that is cost prohibitive. But if tires are found to be noncompliant, NHTSA can order a recall and free replacement of all similar tires. There is also a fine per tire for failure to ensure the tires meet the NHTSA requirements. These penalties could cost a tire company tens of millions of dollars, so there is a strong incentive to comply. This is why tires all have a “DOT serial number.”
There is no way for anyone or any federal agency to establish quality or performance standards that would cover all tires in all sorts of usage. This would be cost-prohibitive to consumers.
Do all tires of the same size support the same load?
The second part of the question concerns the load capacity of tires from different manufacturers. NHTSA uses the TRA-published dimensional and Load/Inflation tables when specifying the tests. Almost all tires must be able to pass those tests. Therefore, you can use the Load Inflation tables from any company and expect that your tires can support the same load. The exception would be those tires from Michelin that were initially developed using metric standards rather than the inch-pounds standards published in the TRA books.
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