I've had a little insight into the tire business through a fishing buddy of mine who has a SIL who is the general manager of a large tire distributor in our area. Some time back we had him with us on one of our outings and I had the opportunity to ask a lot of tire questions while we were sitting around the campfire. So I'll pass on some of his insight ...
The tire industry (and especially trailer tires) have been going through an upheaval the past few years. Moving from US made to places far, far away (especially like China) and has caused some affect in tire quality. Even with those name brands that were still made up to Parr, there were several other off brands that were shoddy at best and even sometimes made with inferior materials. So the advice here was to buy name brand as those manufacturers would stand behind them. Even with the last remaining USA made tires there were problems - Carlile's trailer manufacturing plant in Georgia burned to the ground and while Carlisle was building a new plant in Tennessee they had someone else make their trailer tires for them and put their name on them, which ended up with lots of tires that didn't measure up to standards. But Carlisle still stood behind those defective tires and that is the measure of a honest company. Personally, I've used Carlisle trailer tires for years and for the most part they have stood up well for me. Did have one defective tire about three years ago but Carlisle stood right behind it ... it began to separate right in the middle of the tread and was only about a year old with not that many miles on it.

Here's a site that lists two tires, Charlisle's USA made top of the line tires and a cheaper quality foreign brand.

h ttp://wfww.easternmarine.com/Trailer-Tires-Only-BIAS-PLY/

Glen ~ load range use to be dependent on how many cords the tire had for a particular sized tire. Now with better materials then previous years, the tires are now "ply rated" and reflect that with "load range"

My previous p'up, a '99 Starcraft, had a dry (empty) weight of about 1350 lbs. The total weight it could carry (GVWR) was 2200 lbs, or could carry 850 lbs accessories and cargo. The tires were 5.30 X 12, load range "C", and could carry 1050 lbs each (1050 X 2 = 2100 lbs). The trailer axle and suspension were rated to carry 2,000 lbs ~ hence the 2200 GVWR ... the trailer carrying 2000 lbs and the hitch carrying at least 10%, 200 lbs..  However, I never exceed the capacity of the tires, so 2100 lbs was the max.

Here's a Carlisle Tire website that gives a list of trailer tires showing the tire size, the manufacture product number, then the load range, followed by sizing and other information about that particular tire. Maybe it might be of some help.