Taking Care of Your Trailer Tires

Taking Care of Your Trailer Tires

by Joe Subda

How much thought do you put into your trailer tires? How much attention do they deserve? Trailer tires appear to have an easy life; hey, they spend most of it waiting to go somewhere.When working they just tag along behind you going ’round and ’round without a care in the world.

This would seem like a good way to view your trailer tires until you experience a problem, or worse, a failure. Once you have encountered a problem and/or a failure your view of trailer tires changes and you’ll want to know more about them.

Trailer tires are not the same as automotive tires. Automotive tires must maintain traction during all driving conditions: pulling, stopping, turning, or swerving. These tires are required to have more flexibility in the sidewalls to maintain tread-to-road contact. Trailer tires only need traction when braking, so the sidewalls do not have to be as flexible. Trailer tires have stiff, beefy sidewalls and other structural components to provide stability and handle the stress and dynamics imposed by a towed load. The stiffer sidewalls also add in reducing sway. Trailer tires normally have the designation ST (Special Trailer). Passenger car tires designation is (P) and light truck is (LT). It is recommended that you only use ST tires on your trailer.

ST tires feature materials and construction to meet the higher load requirements and unique demands of towing. The polyester cords used in ST tires are bigger than they would be for a comparable P or LT tire. In addition, the steel wire also has a larger diameter or a greater tensile strength to meet the additional load requirements. This heavier construction for an equal volume of air space, allows an ST tire to carry more load than a P or LT tire.


How do you read or interpret specifications on a tire side wall? This can be a problem because the Trailer Tire Industry uses three different size identification systems on trailer tires. The following are examples and explanations of tire code.

THE NUMERIC SYSTEM: (4.80 x 8) mostly used on smaller trailer tires. 4.80 inches indicates the tire section width, the widest point of the tire. 8 inches is the rim diameter.

THE ALPHA NUMERIC SYSTEM: (B78 x 14 C) common on 13 to15-inch trailer tires. B indicates air chamber size. 78 is the “Aspect Ratio” the Sidewall Height divided by the Section Width. 13

THE METRIC SYSTEM: (ST205 75D 15C) currently being phased in by trailer-tire manufacturers. ST (Special Trailer) indicates the tire application type. 205 is the section width in mm, 75 is the “Aspect Ratio” the Sidewall Height divided by the Section Width. D is the construction type D= bias ply. 15 is the rim diameter and C is the load range.


D – 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.

R – RADIAL: Radial plies run at right angles straight across the tire from bead to bead with belts (usually steel wire) under the tread. This allows for excellent traction and holding tread to the road while you are turning or swerving. These are usually used on a car or or truck, because they need flexible sidewalls.

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BIAS BELTED: Bias belted are constructed with a standard bias ply crisscross. They have bead-to-bead construction, but include additional belts under the thread.

Radial vs. Bias Ply

Today’s trailer tires are available in both bias ply and radial. At one time it was thought that the sidewalls on radials were too soft. The soft sidewalls would allow the trailer to squirm all over the road. This is not the belief now, and today there is more acceptance of radial tires for trailers. The type that you should use will depend on your towing style.

Bias-ply tires provide more side-to-side stability, but run hotter then a radial tire. If you are pulling a heavy load, use a bias ply for an extra measure of stability. If your trailer is lite and you do a lot of long-distance towing at high speeds, the radial design may be better. The radial will stay cooler in this situation then a bias ply. The cooler the tire stays, the less it will fatigue. These are only examples of tire applications; consult your local tire dealer for the tire type that would be best for your towing style and trailer.


The maximum weight each tire can support safely is called the tire load range. The load range, B, C, D, etc. of the tire should be noted on the sidewall. Load ranges are based on the maximum inflation pressure of a tire. The higher the load range, the higher the weight the tire can carry. Below is a table with load ranges of some trailer tires.
It is important to select the proper load range for your trailer.
Proper care and maintenance of your trailer tires is one of the keys to a pleasant and trouble-free towing experience. In addition, a regular check or visual inspection of your tires can help you spot potential problems. Tips for maintaining and caring for your trailer tires are listed below. What to look for during a visual inspection is also discussed.

  • Always inflate trailer tires to the maximum inflation indicated on the sidewall.
  • Check inflation when the tires are cool.
  • Check the tires before each trip. (Under inflation is the number one cause of trailer tire failure.)
  • A tire that is worn on the edges is under inflated.
  • A tire worn in the middle is over inflated.
  • The combined capacity of the tires should exceed, by 20 percent, the loaded trailer weight.
  • Time and the elements weaken a trailer tire. In approximately three 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 three to four years of service regardless of tread depth or tire appearance.
  • Clean the tires using mild soap and water.
  • Tire-care products containing alcohol or petroleum distillates can accelerate the breakdown of trailer tires.
  • The ideal storage for trailer tires is in a cool, dark garage at maximum inflation.
  • When the trailer is in storage use thin plywood sections between the tire and the pavement.
  • If your tires have cracks, get them checked. The cracks could be dry rot.
  • Make sure the valve stem and cap are in good shape. Old cracked valve stems, can break off, leading to a sudden of pressure.

Taking care of and maintaining your trailer tires are the keys to avoiding tire trouble while towing. Equipping your trailer with the proper tires is another way to avoid tire trouble. Replacing your tires every three to fives years even if they do not look worn out is also a good way to avoid tire trouble. Take care of your tires and they will take care of you.

Don’t forget to check your spare.

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