Choosing the right set of tires for any scenario is extremely important. The difference between choosing the right tires for your car and your needs vs. the wrong set of tires can be the difference between crashing and being safe. That cannot be truer with ST trailer tires. Most people that we know assume that installing their truck tires on the trailer will work just fine, but that’s far from the truth.
The ST designation in trailer tires stands for “Special Trailer,” compared to the LT designation of truck tires, which means “Light Truck.” This should give potential buyers enough of an incentive to buy these tires for their trailers. However, to provide you with a better picture of why these tires are essential for safety while towing, we will dive into the details on why ST trailer tires are critical to any trailer.
What Makes ST and LT Tires Different?
ST trailer and LT truck tires might seem identical, but there are a lot of differences inside. LT tires are specifically designed to give your truck better handling abilities. They are much more responsive, thanks to the lower weight of the tire, and offer much better traction, grip, and braking. However, LT-rated tires have smaller load ratings than ST-rated tires, and that’s where the differences start.
ST-rated tires have thicker and stronger polyester cords, as well as steel wires with larger diameters. Both the polyester cords and wires give the tire much better structural rigidity and, therefore, higher load ratings. This means that ST-rated tires can carry heavier loads when compared to LT-rated tires, which makes them a much better choice for trailers.
The biggest reason why the structural rigidity is significant in ST-rated tires is simply that they spend most of the time in one place. While you will use the LT-rated tires on your truck every day, the ones that sit on your trailer will be used much less often, maybe even once per year. When the trailer is stationary, the tires should be able to carry the whole weight of the trailer without becoming distorted.
Choosing the Right Load Range Capacity or Ply Rating
Just like when choosing LT-rated tires, it is essential to select the right load range capacity of ST-rated tires. If you buy tires that aren’t up to the task and don’t have enough capacity for your trailer, they might get distorted very fast. If that happens while you are on the road, the trailer will lose stability or even worse – a tire might get blown out. Suffice to say, if you care about safety while on the road, we recommend always choosing tires that can withstand the whole weight of your trailer with ease.
Today you can find ST-rated tires in several load ranges. Previously, these tires were rated with the “Ply” rating, which signified how many plies were there in a tire. However, modern tires don’t use that standard, only because more plies don’t always equate to a more robust tire. Nonetheless, it’s easy to make an analogy by following the list below:
- Load Range B (4 Ply Tires) – maximum load pressure of 35 psi (240 kPa)
- Load Range C (6 Ply Tires) – maximum load pressure of 50 psi (350 kPa)
- Load Range D (8 Ply Tires) – maximum load pressure of 65 psi (450 kPa)
- Load Range E (10 Ply tires) – maximum load pressure of 80 psi (550 kPa)
Apart from the Load Range rating, we recommend going through the specifications of your trailer and the tire to choose precisely the right capacity you need. All ST-rated tires come with Maximum Load capacity per tire, expressed in lbs or kilograms. To calculate how much weight will carry one tire, just divide the weight of your trailer to the number of tires. For example, if your trailer has two axles and a weight of 8,000 lbs, the tires should have Maximum Capacity of at least 2,000 lbs per tire or more.
Radial or Bias-Ply
Another issue potential ST tire buyer will come up to is choosing between radial and bias-ply tires. The main difference between these competing technologies is how the plies are positioned into the tire. For radial tires, the plies are positioned across the tire, while on bias-ply models, they are placed at a 30° angle across the tire.
But, what does that mean when you put them on the trailer? Well, the main advantage of bias-ply tires is that they are more robust and usually come in higher load ranges. Thanks to that, bias-ply tires can be used on rough terrains, like gravel or dirt. That said, bias-ply tires can also overheat quickly, which significantly reduces overall stability.
Every other advantage goes to radial tires. They are lighter, have longer treadlife, and offer better high-speed stability. For example, if a bias-ply tire lasts for around 15,000-miles, a radial one will last for over 40,000-miles. The lighter weight will have a positive impact on performance and fuel economy, and radial tires won’t overheat much when driven for prolonged periods.
How to Take Care of ST-rated Tires?
As we’ve mentioned previously, ST-rated tires will spend most of their time stationary. That puts a lot of strain on them, and if proper care is not taken, they might get damaged. To be sure that your ST-rated tires will last for long, follow these simple rules:
- Always inflate the tires to the specified pressure. Even when the tires are stationary, the pressure inside changes together with the outside temperature. The lower the heat, the less stress inside, and vice versa.
- Don’t expose the tires to the sun. The higher temperature and UV rays from the sun can oxidize the exterior of the tire, while the heat can help the oxygen inside the casing oxidize the interior, rendering it completely unsafe for the road.
- Check the tread depth with a Lincoln penny. Turn the penny upside down and put it into the tread grooves. If you can see the full head of Lincoln, then you need to replace the tires.
- Even if the tread is fine, replace the tires every 4-5 years. Due to the previously-mentioned oxidation, ST-rated tires lose their ability to properly grip the road after a while, especially in rainy conditions, even if there is sufficient tread depth.
Finally, we recommend always carefully reading the instructions and specifications on your trailer to find tires that are the best fit.