Trailer Choice - Tires 101

ST tires (Special Trailer Tires) are designed specifically for trailers. They have unique features tailored to the needs of trailer applications, including:

Sidewall Strength: ST tires have stronger sidewalls to handle the higher loads and stresses that trailers often experience.

Tread Design: The tread on ST tires is optimized for stability and to minimize sway, rather than traction, which is crucial for trailers.

Durability: ST tires are built to withstand the demands of towing, including higher loads and extended periods of storage.

Bias-ply tires have a construction where the layers of fabric (plies) are crisscrossed at an angle (usually 30 to 45 degrees to the direction of travel). This construction method provides specific characteristics:

Sidewall Strength: Bias tires typically have thicker sidewalls, providing better resistance to punctures and cuts.
Ride Quality: They tend to have a stiffer ride compared to radial tires, which can be less comfortable.
Durability and Stability: Bias-ply tires are often used in applications where durability and ruggedness are more critical than ride comfort, such as off-road or certain trailer applications.
Cost: Generally, bias-ply tires are less expensive than radial tires.

PT (Passenger Tires) and LT (Light Truck Tires) are designed for different purposes:

PT Tires: These are for passenger vehicles and focus on comfort, traction, and handling. They are not built to handle the high loads of trailers.

LT Tires: Designed for light trucks, these tires have stronger sidewalls compared to PT tires and can handle more weight. They are often used on trucks and SUVs but can be used on trailers in some cases. However, they are not optimized for trailer-specific needs like reduced sway and increased sidewall strength.

Ply rating is an older term that refers to the strength of the tire, with modern tires using Load Range designations (e.g., Load Range C, D, E) to indicate this strength. Here is how ply ratings generally correspond to load ranges:

6 Ply (Load Range C): These tires can handle moderate loads and are often used for smaller trailers. They provide a balance between load capacity and ride comfort.

8 Ply (Load Range D): These tires are stronger and can handle heavier loads than 6-ply tires. They are suitable for larger trailers that carry more weight.

Weight Rating (Load Index): This indicates the maximum load a tire can carry at a specified pressure. For example, a Load Range C tire (6-ply) typically has a load index of around 1820 lbs per tire, whereas a Load Range D tire (8-ply) might have a load index of around 2540 lbs per tire.

Speed Rating: This indicates the maximum speed a tire can handle safely. Common speed ratings for trailer tires include:

L: Up to 75 mph

M: Up to 81 mph

N: Up to 87 mph

GVWR 7000 lb Utility Trailer:

ST Tires: Use Load Range C (6-ply) tires if the individual axle weight is around 3500 lbs. Ensure the combined load rating of the tires exceeds the trailer's GVWR.

Example: If using two axles, each tire should have a load rating of at least 1750 lbs.

GVWR 10000 lb Utility Trailer:

ST Tires: Use Load Range D (8-ply) tires. Ensure the combined load rating of the tires exceeds the trailer's GVWR.

Example: If using two axles, each tire should have a load rating of at least 2500 lbs.

Advantages:

Durability: Bias tires are robust and can handle rough terrains well.

Cost: Generally more affordable than radial tires.

Disadvantages:

Ride Quality: They tend to provide a rougher ride compared to radial tires.

Heat Buildup: Bias tires are more prone to heat buildup, which can affect performance on long trips.

For utility trailers, ST radial tires are generally the best choice due to their design and strength tailored for trailer use. For a 7000 lb GVWR trailer, Load Range C (6-ply) ST tires are suitable, while a 10000 lb GVWR trailer requires Load Range D (8-ply) ST tires. Bias-ply tires can be a good choice for rougher terrain or lower-cost applications but may not provide the same ride quality or heat resistance as radial tires. Always check the specific load and speed ratings to ensure safety and performance.

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