Directly from Dicount Tier web page:

http://www.discounttire.com/dtcs/inf...rTireFacts.dos

Trailer Tire Applications
Trailer tires are designed for use on trailer axle
positions only, not for the loads applied to or the
traction required by drive or steering axles.
An 'LT' designation on a trailer tire size specifies
load range only. It is not designed for use on light
trucks.
Do not mount 'ST' or 'LT' trailer tires on passenger
cars or light trucks.
Inflation
Always inflate trailer tires to the maximum inflation
indicated on the sidewall.
Check inflation when the tires are cool and have not
been exposed to the sun.
If the tires are hot to the touch from operation, add
3 psi to the max inflation.
Underinflation is the number 1 cause of trailer tire
failure.
Load Carrying Capacity
All tires must be identical in size for the tires to
properly manage the weight of the trailer.
The combined capacity of the tires must equal or exceed
the GVW of the axle.
The combined capacity of all of the tires should exceed
the loaded trailer weight by 20 percent.
If the actual weight is not available, use the trailer
GVW. If a tire fails on a tandem axle trailer, you
should replace both tires on that side. The remaining
tire was likely subjected to excessive loading.
If the tires are replaced with tires of larger diameter,
the tongue height may need to be adjusted to maintain
proper weight distribution.
Speed
All 'ST' tires have a maximum speed rating of 65 mph.

As heat builds up, the tire's structure starts to disintegrate
and weaken.
The load carrying capacity gradually decreases as the
heat and stresses generated by higher speed increases.

Time
Time and the elements weaken a trailer tire.
In about 3 years roughly one third of the tire's strength
is gone.
Three to five years is the projected life of a normal
trailer tire.
It is suggested that trailer tires be replaced after
3 to 4 years of service regardless of tread depth or
tire appearance.
Mileage
Trailer tires are not designed to wear out.
The life of a trailer tire is limited by time and duty
cycles.
The mileage expectation of a trailer tire would be
5,000 to 12,000 miles.
Why Use An 'ST' Tire
'ST' tires feature materials and construction to meet
the higher load requirements and demands of trailering.

The polyester cords are bigger than they would be for
a comparable 'P' or 'LT' tire.
The steel cords have a larger diameter and greater
tensile strength to meet the additional load requirements.

'ST' tire rubber compounds contain more chemicals to
resist weather and ozone cracking.
Storage
The ideal storage is in a cool, dark garage at maximum
inflation.
Use tire covers to protect the tires from direct sunlight.

Use thin plywood sections between the tire and the
pavement.
For long term storage: Put the trailer on blocks to
take the weight off the tires, lower the air pressure
and cover tires to protect from direct sunlight.
Maintenance
Clean the tires using mild soap and water.
Do not use tire-care products containing alcohol or
petroleum distillates.
Inspect for any cuts, snags, bulges or punctures.
Check the inflation before towing and again before
the return trip.
Three Keys to Avoiding Trouble
Make sure your rig is equipped with the proper tires.

Maintain the tires meticulously.
Replace trailer tires every three to five years, whether
they look like they're worn out or not.