Hi All: I reformatted and added in specific tire data from several web pages from the last post. FYI The following site is the Goodyear page on their Marathon trailer tire.

GOODYEAR: http://www.goodyear.com/nat/i_want_tires/atvgolf/products/trmarathon.html

TOWING, TRAILERING, and TIRE articles at Champion Tire Company. Lots of great data: http://championtrailers.com/techsup.html#article index
Check this out for general tire identification for tires using the P-metric designation (e.g., P245/50ZR16)

TIRE CODE FORMAT
[Code][Width]/[Aspect][Speed][Construction][Size]

Code:
P = Passenger
LT = Light truck
T = Temporary
LTP = Light truck, personal use
ST= Special Trailer;

ST denotes a tire with For trailer application, it is essential that you select the correct tires to match your application and capacity requirements. (ST) Special Trailer tires are normally more expensive than (P) Passenger car or (LT) Light Truck tires because they are built tougher with more material and are more bruise resistant. This is necessary because most trailer suspension systems are stiffer and less sophisticated than automotive suspension systems. Consequently the tires must be capable of withstanding more ABUSE. Trailer Tire requirements differ greatly from automotive tires. Automotive tires must maintain traction during all driving conditions: pulling, stopping, turning, or swerving. Because of this they must have more flexible sidewalls to maintain tread to road contact. Since trailers have no driving torque applied to their axles, the only time trailer tires must have traction is during the application of trailer brakes.

Trailers with heavy loads, high vertical sideloads (like camper trailers), or trailers with inadequate tongue weight can be affected by trailer sway problems. Automotive bias or radial tires with their more flexible sidewalls can accentuate trailer sway problems, whereas the stiffer sidewalls of the ST (special trailer) bias ply tires help to control and reduce sway problems. For this reason it is not recommended that (P) Passenger or (LT) Light Truck tires be used on trailers. Best trailer control will be achieved with (ST) Special Trailer tires.

WIDTH:
Width at widest point, sidewall to sidewall, in millimeters

ASPECT RATIO:
Tire height in mm, measured tread to bead, divided by width above, multiplied by one hundred.

SPEED RATINGS:
(The maximum speed the tire can maintain at its maximum load rating)

Q - 100 mph 160kph
R - 106 mph 170kph
S - 112 mph 180kph
T - 118 mph 190kph
U - 124 mph 200kph
H - 130 mph 210kph
V - 149 mph 240kph
W - 168 mph 270kph
Z - more than 168 mph 270kph (Supersonic Airstreams only!)

Construction:
R - Radial ply
B - Bias belted
D - Diagonal bias

Size:
The diameter of the wheel the tire is designed to be mounted on, in inches.

Other information:
Maximum Air Pressure - This is the max pressure the tire is designed to hold (note this is more than the recommended inflation pressure)

Maximum Load - Weight the tire can support

Load Index - A code that indicates the maximum weight the tire can carry at its speed indicated by its speed rating

Construction - Tells the number and type of plies used in the construction of the tread and sidewall

DOT Serial Number - Identifies the plant, manufacturer, and date of production

Tread Wear Index - A rating of the tire's resistance to wear. 100 is the reference. A 250 rating indicates 2.5 times the wear resistance of the reference tire. This number cannot be accurately translated to mileage.

Traction Index - A rating of the tire's ability to stop on wet pavement. There are three grades, A, B, and C, with A being the best. This index does not reflect the tire's traction performance on dry, snowy, or icy pavement.

Temperature Index - A rating of the tire's ability to dissipate and resist heat. There are three grades, A, B, and C, with A being the best.