Failing tires is one of the main causes of trailering accidents. Having the right tires and keeping them in top condition is key to safe and hassle-free trailering. Due to the rigors associated with trailering, trailer tires are a special breed. Tires specifi-cally manufactured for towing generally bear an “ST” on the sidewall, which stands for “special trailer.”

While the tire industry has established the ST standard for trailer tires, trailer manufacturers are not required to use them. As long as the tire meets the trailer’s load and speed requirements, it’s legal. However, a large number of trailer manufacturers do use ST tires because of their inherent trailering benefits.

When it comes to trailering, one benefit of an ST tire is that it has about 10 percent more load capacity than an equivalent LT (light truck) tire and nearly 40 percent more than a P (passenger) tire. Furthermore, an ST’s mold shape is designed to accommodate trailer wheels, which are typically narrower than P and LT wheels. Being narrow is an advantage on trailer tires, but a disadvantage on wheels that steer and wheels that are attached to the drive axle. Steer and/or drive tires benefit from a larger footprint, which provides the extra traction and performance demanded of them. A free-rolling trailer tire, on the other hand, isn’t called on to turn, swerve and grab the pavement like a steer or drive tire. Since it doesn’t need such a large footprint, it performs its task better by being narrower.

For the same reasons, an ST tire doesn’t have as deep of a non-skid tread as P and LT tires. A deep non-skid is necessary for drive and steer tires in wet environments, because it provides better traction. Again, since a trailer tire is simply free-rolling, it doesn’t need the same degree of traction on wet pavement, and in fact it would be detrimental to its performance. Having a shallower tread depth offers the ST tire two benefits: (1) It doesn’t wiggle as much, which can help reduce sway, and (2) It rides cooler, which adds to its longevity. 

Generally, an ST tire also has somewhat stiffer sidewalls, especially in its lower section. This reduces sidewall flexing, helping it to track straighter and diminish the risk of trailer sway. The stiffer sides also lessen the risk of sidewall blowout.

Your trailer’s spare tire also should not be overlooked. Ideally, it should be the same type of tire as those on the trailer. It’s not good to mix bias tires with radial tires, because they’re designed differently.