Read up on somthing called "Service Index" It will be a number stamped on the side of the tires.
With a radial tire this is the number you need to be concerned with in reguard to tire loading.. The old days of Load Rating were when that equated to the number of plys.
For example I have 2 sets of tires 1 load D the other Load E, both have same number of 'actual' ply construction and BOTH have the same service index 120/119 (IIRC) The double number is the rating when used in SRW/DRW application..
Kudos for doing your homework. I had a shop install P tires on my PSD then try to tell me it was safe..
