“You may have noticed that tight turns with your tandem- and triple-axle trailer put tremendous side loads on the tires. You can see it in the sidewalls or hear it coming from the contact patch. ST tires are designed to handle these side stresses; LTs usually are not.
ST tires are also specifically designed to resist movement that can cause trailer sway, which can be a tremendous advantage in trailer handling”
So in the first part the "ST" are made with flexible sidewalls to cope with the stress of turning. Ok I believe this "may" be true.
In the second part he talks about resisting trailer sway. If a tire has any influence on trailer sway it would be do to sidewall stiffness, which he just said the were designed to not have:S
I think I will keep running LT's :C