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TRAILER TIRE ARTICLE

TRAILER TIRES

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.

TYPES OF TIRE CONSTRUCTION

A.) Bias Ply - Poly or Nylon cords crisscross the tire from bead to bead with the same number of ply at both tread and sidewalls, providing stiffer sidewalls and more resistance to sway.

B.) Bias Belted - Standard Bias Ply crisscross, bead to bead construction, but with additional belts under the tread.

C.) Radial - Radial Plies run at right angles straight across the tire from bead to bead with belts (usually steel wire) under the tread. This provides excellent traction holding tread to road during swerving or turning. These are very important features for controlling a car or truck, but the flexible sidewalls of this type of tire may aggravate trailer sway problems when this type of tire is installed on a trailer.

TIRE SIZE IDENTIFICATION
A.) Originally American tires were provided with numeric sizing (480x12, 600x13, etc.) This gave the section width (the widest point of the tire) and the diameter of the rim. Some smaller trailer tires today still retain that numeric identification (480x8, 570x8, 480x12, 570x12, etc.)

NUMERIC 570X8
570	8
SECTION WIDTH	RIM DIAMETER

B.)Then in the 1960's tire manufacturers and D.O.T. changed most tires to alpha numeric identification to provide more information (B7813C, F7814C, H7815D, etc.)

	ALPHA NUMERIC F7814C
F	78	14	C
Air Chamber Size	Aspect Ratio = Section Height Section Width	Rim Diameter: 13", 14", 15", etc.	Load Range: A, B, C, D, and E, etc.

C.) Finally in the late 1970's and early 1980's, D.O.T. and domestic tire manufacturers converted the majority of tire production to the metric system again providing more information about the tire.

	METRIC ST20575D14
ST	205	75	D	14
Application Type ST- Special Trailer LT-Lite Truck P-Passenger	Section Width: 205 mm 215 mm 225 mm, etc.	Aspect Ratio = Section Height Section Width (70, 75, 80, etc.)	Construction Type: D - Bias Ply R - Radial B - Bias Belted	Rim Diameter: 13 14 15, etc.

ASPECT RATIO = SECTION HEIGHT SECTION WIDTH

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.