Trailer Tire Sizing

Tire Type defines the proper use of the tire. For example, the “ST” on the tire shown here means that this is a trailer tire. "P' = Passenger car, "LT" = Light Truck

Tire Width is the width of the tire measured in millimeters from sidewall to sidewall. This tire width is 205 millimeters

Aspect Ratio is the ratio of the height of the tire's cross-section to its width. On our example, 75 means that the height is equal to 75% of the tire's width.

Sidewall Height / Aspect = Tire Width x Aspect Ratio / 100
= 205 x 75 / 100 = 153.75 mm

Construction tells you how the layers of the tire were put together. The “R” stands for Radial which means the layers run radially across the tire. A “B” stands for bias construction which means that the layers run diagonally.

Wheel Diameter is the width of the wheel from one end to the other. The diameter of this wheel is 15 inches.

Vintage Tire Conversion Chart

RADIAL REPLACEMENT GUIDE
Size	Load @ 50 PSI	New Size	Load @ 50 PSI
SPECIAL TRAILER SIZES/LR-C
B78-13ST	1315 lb.	ST175/80R13	1360 lb.
C78-13ST	1410 lb.	ST185/80R13	1480 lb.

F78-14ST	1710 lb.	ST205/75R14	1760 lb.
G78-14ST	1865 lb.	ST215/75R14	1870 lb.

F78-15ST	1710 lb.	ST205/75R15	1820 lb.
H78-15ST	2035 lb.	ST225/75R15	2150 lb.
SPECIAL TRAILER SIZES/LR-D
H78-15ST	2370 lb.	ST225/75R15	2540 lb.

Use this chart to figure out the closest modern tire size to your original tires. Keep in mind these are close approximations and may not be exact replacements. Before purchasing any tires you should compare outside diameters and the tread footprint to get a better idea on how close a match they are.