Here's a link to Trailer Tires: Tips & Best Practices
There is a lot of good information in the PDF... but keep in mind... Carlisle does not make on road "passenger" tires. Their marketing may be a bit bias and skewed a tad towards selling ST tires.
I agree with the obvious LOAD requirements, i.e. always use tires that meet or exceed the GAWR of the trailer.
I have ST tires on our trailer now... when its time to replace them I may go to an LT tire for a number of reasons.
1. As RKR mentioned... there are numerous accounts of premature catastrophic ST tire failures vs. LT failures.
2. wmtire mentioned cost: "If passenger designated tires were the answer (and legal), then trailer manufacturers would use them, since they are usually cheaper in price and more readibly available."
A good LT tire with a load rating that meets the GAWR of the trailer is considerably more expensive than an ST tire.
In the Cedar Creek line of 5th wheels the heavier models come with G rated LT
tires, "8-Lug, LT, “G” Rated, Goodyear Tires on 7000 Axle Units" and is available as an expensive option on the lighter models.
3. Per the link above... the life expectancy of ST tires is 3-5 years regardless of mileage. If ST tires are so superior to LT tires why is there life expectancy so short?
4. Side wall stress... if you understand physics think about the side wall stress of your front steering tires while cornering at typical driving speeds. There is an incredible amount of side wall stress generated when supporting a heavy duty diesel pick up's 5000 lbs of front axle weight while cornering.
5. ST tires are not required to meet the same government safety test standards as passenger tires. Which makes sense... passengers don't ride in trailers.
So far my ST tires are holding up well... but I'm not convinced ST tires are the only way to go.