A bias ply trailer tire is constructed with nylon belts of the tire running at a 30-45 degree angle of the tread center line.
Bias ply tires feature crosshatch construction, which provides stronger & tougher sidewalls. Due to the design of the tire’s construction,
bias ply tires want to roll straight, as the trailer itself often does. Bias ply tires are generally less expensive.

A radial trailer tire is constructed with the steel belts of the tire running at a 90 degree angle of the tread center line.

Radial tires run cooler. They're steel-belted, which results in a tougher overall construction, a longer tread life, & a wider footprint.