Bias Tires: Comparison and Future

Bias-ply tires (also known as bias-ply tires or conventional tires) are an important category in the history of the tire industry. Their core characteristic is that the adjacent cords of the carcass ply and the buffer ply are arranged diagonally, forming an angle of less than 90° (typically 35°-55°) with the tread centerline.

This classic structure dominated the tire market for a long time, and even now, with radial tires becoming the mainstream, it still plays an irreplaceable role in specific areas.

Structurally, bias-ply tires consist of four core parts: the tread, the carcass ply, the buffer ply, and the bead. The tread, as the surface layer in direct contact with the ground, is divided into the crown, shoulder, and sidewall. The crown uses wear-resistant rubber and features anti-skid tread patterns, bearing the functions of friction, load, and impact cushioning. The shoulder, through optimized tread patterns, achieves both heat dissipation and anti-skid properties. The sidewall, although thinner, must withstand torsional deformation to protect the carcass ply from damage.

The ply layer is the core of the tire's skeleton, composed of multiple layers of rubber-coated cords bonded together. The number of layers is usually even to ensure even load distribution. Early ply layers used cotton yarn, but were gradually replaced by high-strength materials such as nylon and polyester fibers. Reducing the number of ply layers while maintaining the same load capacity lowers rolling resistance and extends tire life.

The buffer layer, located between the tread and the ply layer, is made of sparsely spaced cords and highly elastic rubber. It cushions road impacts and prevents the tread from separating from the ply layer during emergency braking. The bead consists of a steel wire ring, ply layer edging, and bead wrapping, securing the tire firmly to the rim with high rigidity and strength.

In terms of performance, the structure of bias-ply tires determines their distinct advantages and disadvantages. Advantages include high longitudinal rigidity, good tread and sidewall integrity, outstanding load-bearing capacity, especially stable pressure resistance under low-speed, heavy-load conditions, simple structure, low manufacturing cost, and high ease of maintenance.

However, its shortcomings are equally significant: due to the cross-arrangement of the cords, the interlayer friction is intense at high speeds, leading to heat generation and poor heat resistance; the unstable contact patch results in insufficient grip; uneven stress on the tread limits its wear resistance and lifespan; and the high sidewall stiffness results in poor riding comfort, making it unsuitable for high-speed driving.

Compared to modern mainstream radial tires, the core differences lie in their structural design and performance. Radial tires have radially arranged cords (at a 90° angle to the tread centerline) and an independent steel belt layer in the crown, separating the crown from the sidewall.

Therefore, they offer advantages such as a large contact patch, low rolling resistance, high wear resistance, and good fuel economy, but the sidewall is more fragile, resulting in slightly poorer lateral stability. Bias-ply tires, on the other hand, are characterized by high overall carcass rigidity and robust sidewalls, making them more adaptable to impact loads under complex road conditions; however, their overall performance has been surpassed by radial tires.

This difference directly leads to a divergence in application scenarios: radial tires are widely used in passenger cars and high-speed commercial vehicles, while bias-ply tires remain only in low-speed heavy trucks, construction machinery, and agricultural machinery—fields with lower requirements for high-speed performance but higher requirements for load-bearing capacity and impact resistance.

From an industry development perspective, bias-ply tires originated in the late 19th century, became the mainstream tire type for automobiles in the early 20th century, and saw significant performance improvements in the mid-20th century with the application of synthetic rubber and high-strength cord materials, ushering in a golden age of development.

However, since the advent of radial tires, their market share has gradually shrunk, and they have now withdrawn from the mainstream passenger car market, maintaining demand only in specific industrial and agricultural sectors. However, technological iteration has not stopped.

Modern bias-ply tires, through material improvements (such as the use of new synthetic rubbers) and process optimization, continue to improve in terms of load-bearing efficiency and aging resistance to meet the specific needs of professional scenarios.