There is a significant difference between bias ply and radial ply tyres. The so-called cord angle, defined as the angle formed between the single cord plies of a carcass fabric with the center line of the circumference of the wheel, plays a decisive role. In the case of radial ply tyres the cord angle amounts to 85°-90° while with bias ply tyres is it about 20°-40°. Fig. 1-2 shows the design of a passenger car's radial ply tyre and the function of the individual components.
While radial ply tyres are reinforced in the tread area by a suitable belt, in the case of bias ply tyres it is necessary to stiffen or increase the number of plies in the entire carcass including the load carrying sidewall. This explains the larger spring stiffness of a bias tyre. At the same time it causes increased internal friction, a stronger damping, and thus a larger flexing resistance.