Hi, Eric,
Here's a link to a fairly definitive article on trailer tires:
http://www.discounttire.com/dtcs/inf...ionAnxiety.dos
As you can see, it states that trailer tires are indeed optimized for
load, and that for the same dimension an ST tire carries more load
than a P or LT tire.

You're right that ST tires have a speed limit of 65 mph. If you want
to exceed 65 mph, then you do indeed need a different tire rated for a
higher speed. But from the above, you need to select a bigger
dimensioned tire to handle the load properly. I can't find the source
right now, but I read somewhere that you need to derate the load
rating of a P or LT tire by at least 20% if it's on a trailer.

-John

On Jul 23, 2:21 pm, Eric Greenwell wrote:
Trailer tires (ST designation) don't necessarily run cooler that LT or P
rated tires. Their optimization tends towards longer life (years, not
miles) because they typically aren't used as much or as often as car or
truck tires. They are not optimized for speed, and the load rating has
to be derated over about 65 mph.

My experience with ST tires recently led to me use LT tires instead, but
with a speed rating well above (say, 20 mph) my towing speed. The speed
rating ensures the tread has good lateral stiffness for stable towing
and plenty of margin to avoid tread separation.

Eric Greenwell - Washington State, USA