Bias-ply refers to a type of tire construction where the layers of fabric, or plies, are arranged diagonally. This design allows for flexibility and a larger contact area with the road, which can enhance traction and ride comfort. Bias-ply tires are commonly found in older vehicles and certain types of trailers. Unlike radial tires, where the plies run perpendicular to the direction of travel, bias-ply tires have a crisscross pattern. This can lead to a softer ride but may result in less stability at high speeds. Bias-ply tires are often used in classic cars and off-road vehicles for their unique performance characteristics.