Tow Far - Trailer Tires

It's obvious that not all tires are created equal. There is great disparity in quality and purpose. Although less understood and appreciated, the same holds true for the tires on your trailer. Because of a trailer's lowly and functional appearance, its tires may not get the attention they merit. However, the first time we experience tire failure and find ourselves panic-stricken by an out-of-control trailer, we'll suddenly give them a whole lot more thought. Fortunately, there are better, less adrenalin-raising ways to learn about the distinct features of trailer tires.

The "ST" Sign
Look at the sidewalls of the tires on your car or truck, and you'll likely notice a "P" or "LT" designation. P stands for "passenger" while LT indicates "light truck," meaning they are designed for those specific types of automobiles. A look at your trailer tire sidewall, on the other hand, will likely reveal a "ST" designation, which stands for "special trailer."


ST tires are made specifically for use on trailers and differ considerably from automotive tires. Therefore, tire manufacturers—at least those that bother to make ST tires—strongly discourage the use of anything but ST tires on trailers. About the only exception is when an ST tire is not available for a particular extra-heavy application, such as single-axle trailers with an unusually large load that surpasses the capacity of an ST tire. In those cases a commercial grade truck tire is usually best.


While the tire industry has established this standard for trailer tires—the ST—trailer manufacturers are not required to use them. As long as the tire meets the trailer's load and speed requirements, it is allowable by law. However, the majority of trailer manufacturers do use STs because of the tire's inherent trailering benefits.

Benefits
One of the benefits of an ST tire when it comes to trailering is that it has about 10 percent more load capacity than an equivalent LT tire and nearly 40 percent more than a P tire when each is filled to its maximum psi rating.