Tyre construction — understanding bias ply tyres In a bias ply (cross-ply) tyre, the cord plies are arranged so that:

Introduction / Context:
Tyre performance depends strongly on carcass construction. Bias ply and radial ply designs differ in cord orientation, affecting stiffness, heat buildup, handling, and durability.

Given Data / Assumptions:

• Bias ply is also called cross-ply.
• Cord plies are typically nylon, rayon, or polyester in automotive applications.
• Steel belts are associated primarily with radial tyres.

Concept / Approach:
In bias ply tyres, cords in successive plies cross each other at an angle (often 30 to 40 degrees) to the circumferential direction. This criss-cross arrangement gives a stiffer sidewall and tread coupling, but generates higher heat at high speeds compared to radials. Radials have cords at roughly 90 degrees to the circumference and use steel belts under the tread for stiffness.

Step-by-Step Solution:
Identify tyre type: bias (cross-ply).Recall standard construction: alternating diagonal plies crossing each other.Choose the option that states 'one ply diagonally one way and another diagonally the other way'.

Verification / Alternative check:
Tyre manufacturer cutaway diagrams show the characteristic crossed ply angle of bias tyres and steel-belted radial structure as distinct alternatives.

Why Other Options Are Wrong:
Parallel plies describe neither bias nor radial tyres. Steel belts are typical of radials, not bias tyres. 'All of the above' cannot be correct because the statements conflict.

Common Pitfalls:
Confusing steel-belted radial features with bias ply; assuming cord angle is the same for all tyres; overlooking the impact on ride comfort and heat generation.

Final Answer:
one ply layer runs diagonally one way and another layer runs diagonally the other way