What’s the difference between bias ply, steel-belted bias ply, and radial trailer tires?

Trailer tires (designated ST – Special Trailer) are not the same as passenger or LT (Light Truck) tires. They are designed specifically for towing, with stiffer sidewalls to handle vertical load and reduce trailer sway. LT tires, by contrast, are designed for vehicles that steer, brake, and accelerate. Using LT or passenger tires on a trailer can lead to instability, premature wear, and unsafe handling.

Within ST trailer tires, there are three main construction types: bias ply, steel-belted bias ply, and radial. Each has unique characteristics:

Bias Ply Tires

• Construction: Two or more layers of nylon cord crisscrossing at 30–38° from bead to bead.
• Performance: Strong sidewalls, rugged for rough terrain, but generate more heat and wear faster at highway speeds.
• Boat Trailer Note: Good for short hauls, gravel ramps, or seasonal/local use.

Steel-Belted Bias Ply Tires

• Construction: Bias ply structure reinforced with two steel belts under the tread.
• Performance: Stronger carcass, improved puncture resistance, more stable than standard bias.
• Boat Trailer Note: A “middle ground” option—better for mixed terrain, but less common today.

Radial Tires

• Construction: Steel belts run at 90° to the tread centerline, allowing sidewalls and tread to function more independently.
• Performance: Cooler running, longer tread life, smoother ride, better fuel efficiency.
• Boat Trailer Note: Best for highway towing, heavy loads, and frequent long trips.

Why ST (Trailer) Tires Are Different from LT (Light Truck) Tires

• Load Handling: ST tires are built with stiffer sidewalls to control sway and support vertical load. LT tires flex more, which benefits ride comfort in a truck but creates instability when used on a trailer.
• Durability: ST tires are rated for heavier loads at higher inflation pressures than LT tires of the same size.
  Heat Resistance: Radial ST tires are engineered to dissipate heat under sustained load, reducing the risk of blowouts—critical for trailers that carry heavy boats.
• Tread Design: ST tires are optimized for straight-line towing, not cornering or traction like LT tires.
  Bottom Line: Always use ST-rated tires on your boat trailer. LT or passenger tires are not designed to handle trailer-specific stresses.