ST tires have load specs that were established when 55 was the Highway speed limit. ST tires have a MAX speed rating of 65mph. This does not mean average but MAXIMUM. This is like engine redline. While it is possible to run your engine right at and even above the redline we all know that we would be significantly reducing the engine life.
The OP said 70 psi when he checked. But that was probably a hot pressure. Because of unique tire loading on multi-axle trailers ST tires should be limited to 85% of the sidewall load and the COLD inflation should always be set to the sidewall max. So his cold infl was probably closer to 60 rather than the 80 it should have been for a LR-E tire. 20% low on inflation is technically "flat" as far as the tire industry is concerned.
Just because tou overload or under-inflate your tires does not mean they will fail immediately but the damage has been done, is cumulative and non-reversable.
ST tires are lighter for a couple of reasons. The tread is narrower (and the tread depth is shallower so they generate less heat at the higher load.
If / when you have a tire failure it will help the couple of tire engineers here to offer informed comments if you post a picture like this.
or this
to help you understand the probable reason for a failure.
There are blogs and even videos out there specifically on RV tires. Educate yourself or you can expect to pay the price of "assuming" you know the facts because someone told you something over a beer or 4 around a campfire.
