Being an old tire engineer I would like to make a comment. Tires marked ST (ST235/85R16) for trailer use are engineered and tested to a lower standard than tires marked Light
Truck, LT (LT235/85R15) or passenger tires for that matter.
*Convince yourself of that fact by reading the words on the side of trailer tires "For Trailer Use Only". Since trailers do not carry passengers, the manufacturer of trailer tires has less liability when a tire fails than when a light
truck or passenger tire fails.
Now look at that construction description on the sidewall. An LT tire will usually say, 3 tread plies, 2 steel 1 nylon. A radial ST tire will not have the nylon ply. The nylon cap ply is there to make sure that the tire stays together in case of a separation failure.
People talk about ST tires being more stable. Stability is a function of air pressure. More air is better. Right up to the maximum pressure listed on the sidewalk. In fact you can go even 5 psi more than the max listed because that higher pressure is recommended in the tables for vehicles traveling continuously at high speed.
Considering the above, it is always better to use an LT tire instead of an ST tire and LT tires are usually cheaper because they are made and sold
in greater volumes.
For small trailers if you can't find a suitable LT tire, use a passenger tire instead of ST if you can find one that can carry the load.