OP wrote:
I’m thinking that I should move up to Load Range E tires for the extra capacity.
Good idea on a trailer that size.
Should I replace just the one that failed or all 4? We probably have right around 8-10K miles on the tires, which are 6 years old.
If your tires are ST type they have timed out. ST tires that old and carrying the weight yours are carrying is a good bet others will have the same issue. We see this a lot on all the trailering websites.
Time for all new tires.
Should I consider Radials or BiasPly?
Bias ply are from another era. For a road trailer the radial tire is the way to go.
The Endurance and Carlisle HD have been out for around two years and so far are popular. Neither has been around long enough to see what kind of service record they will have for the long haul (4-5 years and 20k-30k miles). I'm betting both will have a much improved service record.
The Providers have been out since the '10/'11 era are the first of new gen higher speed rated ST class tires. Like many new ST/LT class tires they became popular on haulers webs first and finally trickle down to rv forums.
I have a 10k car hauler (9460 lbs on the axles) with Provider ST235/80-16 E tires with 30k-32k miles on them. I just got off a 623 mile run on a job at 70-75 mph speeds. After 5 years of trouble free service I'm looking to replace them with same.