Had a question on tire "Quality" and load capacity
"I have been under the impression that a certifying agency, American tire and rim?? Sets the standards in the US and then all tires sold in US must be designed to those standards. So a cheap unknown brand load range D tire from Wal Mart would have the same load and inflation specifications as a Firestone tire from a Firestone dealer?
Tire & Rim Assoc. only lists dimensional standards and the Load & Inflation tables.This is a private industry Association
DOT (US Gov) has a dept, NHTSA (National Highway Traffic Safety Administration) that published tests and performance requirements. I would consider these to be one measure of "Quality"
All tires for highway use, sold in the US must be certified by the tire MFG to be capable of passing the NHTSA tests. The "DOT" symbol on a tire is the indication, from the MFG that the tire was capable of passing any of the NHTSA test when the tire 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 non compliant NHTSA can order a recall and free replacement of all similar tires. There is also a fine per tire that could be charged to the tire company for failure to ensure the tires meet the NHTSA requirements. These penalties could cost a tire company tens of millions so there is a strong incentive to comply. This is why tires all have a "DOT serial" number.
It is important to remember that 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 and still end up with tires that people could afford to purchase.
The second part of the question concerns the load capacity of tires from different manufacturers. Since NHTSA uses the TRA published dimensional and Load/Inflation tables when specifying the tests, all tires must be able to run and pass, you can expect that with the exception of a handful of tires, most from Michelin that were initially developed using metric standards rather than the inch-pounds standards, published in the TRA books that you will find that you can use the Load Inflation tables from any company and expect that your tires can support the same load.