so when looking to switch if my tires I have now are 235/80R16.. what size of LT tire should I be looking for since that size is exclusive to st tires.
Your ST235/80-16 probably is a load E and may have 3400-3600 lbs capacity. As mentioned several times a same size ST won't have the same capacity as a LT235/85-16 E at 3042 lbs capacity.
However if your trailer has 5.2k or 6k axles then the LT235/85-16 E or the LT245/75-16 E both have 3042 lbs capacity have always been a good replacement.
The LT 235/85 is around 31.7" tall vs the LT245/75 @ 30.7".
Also as noted if your trailer has 7k axles then a 16" LT E won't work.
ST E have stiffer sidewalls than same size/load range LT E is simply internet myth.
And of course a 16" Sailun S637 load G has a much stiffer sidewall then a 16" LT load E.
Goodyears G614 LT235/85-16 load G is about the same weight as the Sailun and same stiff sidewall.
ST and LT both have the same bead unseating resistance tests/strength tests per FMVSS 571. Both pas those tests.