AMEN Dick Butler!! The pressure in these trailer tires is absolutely the most important aspect of towing our junk.
I'm unfortunate that I didn't do my research before buying my trailer and have two 5200 lb axles on a 26 footer. It came with Goodyear Marathon and I blew the hell out of tires trip after trip. I discovered this notice from Goodyear:
http://goodyear.com/rv/pdf/marathon_gen_info_032806.pdf
I run the 15" ST225 tire at 70psi cold. Since then I monitor the tire pressure EVERY time I stop and EVERY time before pulling out to or from a race. I even pull over into rest areas occasionally just to check the tires. Since then, I have not had a single blow out (knock on wood... next trip I'm doomed). I also try to pull no faster than 65, and NEVER go over 70 (fortunately my motorhome is hard pressed to go that fast unless its falling off a cliff).
Next trailer will have the heaviest load rated axles and tires I can get even if I'm not hauling anywhere near the rated load.
Don't skimp on the axles and tires!!!