Correct me if I'm wrong, but aren't all tires of the same type (ST/LT) and the same size (225 75R15) and same load range (C,D,E) rated just the same (as to weight capacity) regardless of manufacturer?
No, the load capacity is not always the same between mfgs. I see this on my truck tires - 265/70R17. Capacity ranges between 3300 to 3400 per tire. Not a lot of difference, but there is a difference. I noticed the same thing when I recently bought 16" TT tires.