Buying guide for best trailer tires
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Tires are designed to handle such variables as traveling at different speeds, safely navigating different terrains and road conditions, and carrying different size loads. Trailers, which carry heavy loads, need different tires than the ones on your passenger car.
A good trailer tire, or ST tire, has a thick construction and a high speed rating. But with so many different trailer tires available, how do you find the right one for your trailer? If you’re feeling overwhelmed, we’re here to help.
At BestReviews, we simplify shopping with our handy shopping guides, which are packed with key information and helpful tips. For everything you need to know about trailer tires before you buy, just keep reading.
What are trailer tires?
Trailer tires have a different function than other types of tires. With passenger cars and light trucks, you need tires with good traction to start, stop, and steer the vehicle without slipping. Another main concern with passenger car tires is comfort. The sidewalls of passenger tires are more flexible to absorb the bumps of the road.
A trailer tire, on the other hand, doesn’t need as much tread for traction since it is not responsible for starting or stopping the vehicle. With less traction, there is more room for reinforcing layers like plies and belts. This results in stiffer sidewalls, which are less effective at absorbing any bumps. The additional structural material allows trailer tires to carry a heavier load.
Matching trailer tires to your trailer
Tires are identified by a sequence of letters and numbers found on their sidewalls. Use this code to match new trailer tires to your trailer.
Tire type
The type of tire is indicated by the first letter in the identifying code: P for passenger car, LT for light truck, or ST for special trailer. For trailer tires, look for tires that start with ST. For example, the code ST205/75R15 D/8 would indicate a specialty tire.
Tire width
Listed next is the width of the tire in millimeters. If the code is ST205/75R15 D/8, the width of the tire is 205 mm.
Tire height
The number following the slash indicates the tire’s height. This number is not a measurement, however. It’s the percentage of the tire’s width. In our example, ST205/75R15 D/8, the height of the tire is 75% of its width of 205 mm.
"The tire load capacity on a single axle is cumulative. For example, if you have two trailer tires rated for 1,520 pounds on a single axle, together they can support a 3,040-pound load."
STAFF
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Tire construction
The next letter will either be R or D. These letters let you know how the tire is constructed on the inside. R stands for radial, and D stands for diagonal bias. In our example, ST205/75R15 D/8, we have a radial tire.
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Radial tires: Radial tires have rubber-coated steel cables running perpendicular across the tire. They are better for long distances because they stay cooler and provide less rolling resistance, which means they help with fuel efficiency. They also resist developing flat spots better than diagonal bias tires, and they have a longer tread life of about 40,000 miles.
- Diagonal bias tires: Diagonal bias tires have layers of nylon textile cords that crisscross at 30° angles. They are better for short distances and work well for off-pavement situations, which makes them a good choice for construction vehicles. Diagonal bias tires have a shorter tread life of about 12,000 miles.
Wheel diameter
The last number in the sequence before the space is the diameter of the wheel in inches. In our example, ST205/75R15 D/8, the wheel is 15 inches in diameter.
Load range
The load range is listed after the space. It’s a letter and number that indicates how many plies the tire has. For instance, load range B has four plies, load range C has six plies, load range D has eight plies, and load range E has 10 plies. This number has nothing to do with tire size. It tells you the maximum tire pressure and weight each tire can carry. Two tires can be the exact same size, but the tire with more plies will be able to haul a heavier load. In our example, ST205/75R15 D/8, the tire has a D load range or eight plies.
Expert Tip
Just because the gross trailer weight (the weight of a fully loaded trailer) is below the recommended limit, that doesn’t necessarily mean your trailer tires and vehicle are safe. The load in a trailer must be properly distributed front to back and side to side to avoid unintentional damage to your trailer tires.
STAFF
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Features to consider for trailer tires
Speed rating
While older trailer tires were only rated to travel at a maximum speed of 65 miles per hour for sustained periods, many newer trailer tires are designed and manufactured to travel at higher speeds. A new trailer tire will have a letter on its sidewall that indicates its speed rating: M for 81 mph, L for 75 mph, and J for 62 mph. This rating is for normal inflation and load conditions and good road conditions. Traveling at a higher speed than indicated may cause heat to build up, which can lead to sudden tire failure.
Tire pressure
Trailer tires are designed to function best with the proper inflation. Under-inflated tires will create more friction, causing overheating. This can lead to premature wear and a possible blowout. Over inflation will cause the tires to wear more quickly along the center treads.
Date manufactured
Locate the date of manufacture on the sidewall of your trailer tire. It will look something like this: DOT K3AP 1218. The last four numbers tell you the week and year the tire was manufactured. In our example, DOT K3AP 1218, the tire was made the twelfth week of 2018.
Tread wear
Trailer tires are unique in their tread wear. Since many trailer tires sit most of the year, the tread may look exceptional. Even after a number of years, the tires may appear new. However, since tires naturally break down over time, regardless of the tread wear, it is important to know when they were made. Most manufacturers recommend replacing trailer tires at least every five years, no matter how much tread is left.
Price
Radial trailer tires range in price from just under $50 to about $150. Diagonal bias trailer tires range in price from just under $40 to about $120.
Trailer tires need to be replaced in sets. When you replace one tire on an axle, the other tire on that axle should be replaced as well.
FAQ
Q. When should I check the tire pressure in my trailer tires?
A. Not only should you visually inspect your trailer tires before every trip, but you should also check the pressure in each tire, too, by using a tire pressure gauge. For the most accurate reading, check the pressure when the tires are completely cool.
Q. My trailer tires are new. That means they won’t leak, right?
A. Unfortunately, even brand-new trailer tires can lose air. Heat, cold, heavy loads, and long driving distances can all contribute to your tires losing air.
Q. What is a flat spot?
A. A flat spot is an area of your tire that has become flat due to the weight of the vehicle pressing down on the tire for an extended period of time. This typically occurs when the parking surface is cold. Flat spots can easily happen with trailer tires because trailers tend to sit for extended periods of time. In most cases, these flat spots will round out again after the tire has heated up from traveling. However, a flat spot can be permanent. A permanent flat spot could be a sign of damaging moisture buildup, especially if the trailer is parked in the grass.
