I think there is a conversion chart that would be real helpful. What leads me to think this is the hardest case of them all here. The 6K axle that comes with ST tires rated anywhere from 3420 to 3520 (I think that is the number FE gives for the Towmaster) each. As CapriRacer has pointed out, the sizes of the LT tires don't match those of the ST, so there is no apples to apples comparison.
We know when replacing an ST tire that has a particular max load rating on the sidewall with an LT tire that has a load rating listed on the sidewall that is higher that is an OK situation. That one is a no brainer. The problem is when the load rating on the LT sidewall is a little less. It may actually be if you could recalculate the load of the LT using the K factor for the ST, it might actually be a step up and be OK. The problem is we don't have a chart for this.
For P rated tires, it has long been established that when putting a P tire on a trailer, you divide the load rating by 1.1. So we need a chart that shows each LT tire, the inflation pressure for maximum load, its maximum load rating as an LT tire in single wheel use, and what its maximum load rating would be if its designation was changed to ST. I think only Roger or Barry could provide such numbers, and I don't think they could be obtained from an existing TRA chart, I think they would have to go back to the actual mathematical formulas and know the actual values of K in order to do it.
I would be willing to start the chart by making a chart of the various LT tires, their size, inflation pressure for max load, and their max load (from LT calculations) at that inflation pressure. Roger and Barry would only have to populate the last column. Such a table would make it real easy to determine if one were going the wrong way when trying to choose an LT tire to replace an ST when in the situation where it is not obvious.
