Just a reminder - Ply rating has nothing to do with how many physical plies a tire has.  So don't think your tire has two plies even if it says 'two ply rated'

Todd

From the goodyear tire site:

 How does ply rating relate to load range and the actual construction of a tire?

'Ply rating' and 'load range' are synonymous. Both relate to the load carrying capacity of the tire. Below is the definition of 'ply rating' as taken from the 1950-51 Tire and Rim Manual:

The term "Ply Rating" is used to identify a given tire with its maximum load when used in a specific type of service. It is an index of tire strength and does not necessarily represent the number of cord plies in the tire.

The following is the definition of 'load range' as taken from the 1973 Tire and Rim Manual:

The term "load range" with a letter (A,B,C, etc.) in tire identification is used to identify a given tire with its load and inflation limits when used in a specific type of service, as defined in headings of TRA tables.

In summary, the 'ply rating' and 'load range' are indicators of the actual load capacity of the tire. This rating has no direct relationship to the number of plies.

For proper fitment the tire must have a load capacity capable of carrying the maximum load of the vehicle in service. Both the load and speed capability must be considered in the fitment of a tire as there is a direct relationship of load and speed. All vehicles, on the highway, are required to identify the proper tire size and load requirements on the placard found in the driver's door.