The intent of ST tires was to be better then P tires and they are, unfortunately we have the example like our local rv supply house telling customers that 'there is a fine for using anything but ST tires on a trailer',which I believe stems from - you must use ST instead of P tires on your trailer .
Funny part to the story was the fellow stating, you will be fined for using LT's was standing in front of a Carriage Carri-lite with LT 's on it - what about that trailer I asked ?
Guy did a guppy imitation.