Tire Rack has a pretty good set of tech articles for the layman at this link:
http://www.tirerack.com/about/techcenter.jsp
FYI I've cut & pasted the one explaining the Trailer vs Passenger Tires tires below, since it's germane to this discussion. They seem to endorse both ST & LT for trailer use, but I've heard the opposite for the same reasons explained by them below for ST vs. passenger tires. I'm still looking for where I saw the ST vs. LT article(s), which may have been on the tire mfgrs' associations' website. Perhaps they too have changed their tune on using LT tires on TTs since I previously researched them?
When looking into which tires to put on our Avion T20, I both researched & asked around with a lot of people very expert in vintage trailers - as well as other owners of vintage trailers - and most felt that the Maxxis ST's were the best out there. A few with restored vintage TTs use LT tires, & some use old school vintage repro bias ply tires for the authenticity - some of which are passenger & not truck tires (or radials that look like bias). Although I see here & elsewhere on this site that others have had problems with the Maxxis ST's too.
Most were not keen on the GYMs of late since the early to mid-2000's, & flat out told me to stay away from the budget off-brand ST tires, such as the "$68.59 15" Hi-Run Long March" ones featured in the current CW ad. There are other "off-brands STs out there if you google for an ST tire size.
I don't know about the Hankook STs in that ad, but their car & LT tires are very good for those applications. I think Michelin may make ST tires for EU & other RoW applications, but have never seen them sold here (they may??).
So far I'm happy with the Maxxis ST's 8PR tires, & they provide an adequate cushion over our T20's GTW.
<snipped from:
http://www.tirerack.com/tires/tirete...jsp?techid=219 >
Tire Tech Information/General Tire Information
Trailer Tires vs. Passenger Vehicle Tires
There are differences in the driving requirements between the tires on your trailer and those on the car or light truck you used to tow it. Therefore there are distinct differences between the way trailer tires and tow vehicle tires are engineered.
Your tow vehicle is a leader, which means traction is a key focus in the design of its tires. Traction allows your tow vehicle to accelerate down the road, turn around the corner and brake to a stop. Another important consideration is tow vehicle tires are designed for ride comfort, which is achieved in part by allowing their sidewalls to flex.
Your trailer is a follower, which often makes tire sidewall flexing a negative. Sidewall flexing on trailers, especially those with a high center of gravity (enclosed/travel trailers) or that carry heavy loads, is a primary cause of trailer sway. Typical passenger radial tires with flexible sidewalls can accentuate trailer sway problems. The stiffer sidewalls and higher operating pressures common with Special Trailer (ST) designated tires help reduce trailer sway.
Also consider that Special Trailer (ST), as well as Light Truck (LT) tires are fully rated for trailer applications. This means ST- and LT-sized tires can carry the full weight rating branded on the sidewalls when used on a trailer.
However when P-metric or Euro-metric tires are used on a trailer, the load capacity branded on the sidewalls must be reduced by 9%. This means P-metric or Euro-metric tires with a maximum branded load rating of 1,874 lbs. for use on a car is only rated to carry 1,705 lbs. when used on a trailer.
Comparing the load capacities of a pair of tires of the same dimensions fitted to a single axle trailer,
ST225/75R15 Load Range C-sized tires inflated to their maximum of 50 psi provide 4,300 lbs. of load capacity, where
P225/75R15 Standard Load-sized tires inflated to their maximum of 35 psi would be limited to 3,410 lbs. of load capacity, a total reduction of 890 pounds.
Trailers will be more stable and pull better on tires designed specifically for trailer use. Since Special Trailer (ST) tires are constructed with heavier duty materials, they are tougher than typical passenger vehicle tires. This is a plus because trailer suspension systems are generally stiffer and less sophisticated than automotive suspension systems.
Special Trailer (ST) Tire Speed Ratings
Industry standards dictate tires with the ST designation are speed rated to 65 MPH (104 km/h) under normal inflation and load conditions.
However Goodyear Marathon and Power King Towmax STR tires featuring the ST size designation may be used at speeds between 66 and 75 mph (106 and 121 km/h) by increasing their cold inflation pressure by 10 psi (69 kPa) above the recommended pressure for the rated maximum load.
Do not exceed the wheel’s maximum rated pressure. If the maximum pressure for the wheel prohibits the increase of air pressure, then maximum speed must be restricted to 65 mph (104 km/h).
The cold inflation pressure must not exceed 10 psi (69 kPa) beyond the inflation specified for the maximum load of the tire.
Increasing the inflation pressure by 10 psi (69 kPa) does not provide any additional load carrying capacity.
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