Stress and strain patterns developed in each of several regions of automobile tires have been mapped by using methods particularly suited to each region. Miniature force transducers were used to measure (1) the cord stresses due to shaping tires during vulcanization, (2) the change in cord stress patterns caused by postinflation, and (3) the cord loads caused by tire inflation and by cornering. Liquid metal gages were used to measure rubber strains on tire surfaces. A photoelastic method was used to measure the strain distribution interior to the tire under simulated load. In each of these procedures, particular attention was given to the differences in properties among bias, belted bias, and radial ply tires.
Tire rotation is impeded by a drag force of 10 to 20 lb per 1000‐lb load in normal vehicle operation. The principal cause is hysteresis, which is a function of the viscoelastic properties of the rubber and cord components, the way these materials are used in the tire, and the way the tire is operated. The influence of material properties has been well documented, and many laboratory tests have been developed for their measurement. Of even greater importance to energy losses, however, is tire construction. This subject is developed by consideration of the forces and moments involved in tire operation and of the mechanisms of energy loss. The importance of service conditions is emphasized by a discussion of the factors influencing rolling resistance. Tire rolling losses can be an important fraction of the total power consumption in low‐powered vehicles. Future trends in tire engineering, and their effects on rolling resistance, are discussed.
Fundamentals of composite material technology are applied to the investigation of multi‐ply cord‐reinforced rubber systems as used in pneumatic tires. The stiffness parameters of such multi‐ply systems are determined through the use of the elastic properties of the constituent cord and rubber components. The effects of coupling between the bending and stretching modes of deformation are discussed along with the limitations of present composite material technology as applied to soft rubbery systems. The predicted stiffness parameters are related to tread wear, obstacle envelopment, vibration, and stress analysis of tires.