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The paper has two objectives - (1) to describe the manner in which tires are involved in the “torsional nibble” disturbance an occasional problem in vehicle development, and (2) to illustrate a generally applicable approach for diagnosing the relationships between tire properties and subjective disturbances.

Engineers who are developing new models of vehicles invest considerable effort in adjusting the steering characteristics to conform with specific commercial objectives. In this process, tires have to be redesigned so that their steering properties match the requirements imposed by the physical nature of the vehicle and the subjective reactions of test drivers. One method for the identification of the underlying physical system, and the determination of the required tire properties proceeds by the general approach outlined in the paper.

The paper presents data showing the effects of the state of wear, structure, load, and inflation pressure on the cornering stiffness and aligning torque stiffness of typical passenger tires. A method is introduced and applied for assessing contributions of local elements of the tread interface to the cornering force, the cornering stiffness, the aligning torque, and the aligning stiffness. There is also a further identification of the contributions to the aligning torque from fore and aft interfacial stress distributions and from lateral stress distributions. Pneumatic trail is redefined in the light of the interfacial measurements, and values are established for various operating conditions, states of wear, and tire types.

A method is derived and confirmed for predicting the tread wear configurations of tires positioned on nondriven axles of passenger vehicles. The method is based on laboratory measurements of the interfacial stresses of freely rolling tires and takes account of perturbations in these stresses that occur during the road test procedure. Wear is found to occur primarily at the exit end of the tire-road interface, and the degree of wear is related to the interfacial pressure and slip determining conditions at that location. The steering properties of the tire also enter into the determination. Abrasion resistance of the rubber, temperature, character of the road surface, the test course, and the procedure all appear in the equations of wear in aggregate as a coefficient. In addition, there are interference effects between adjacent ribs of the tire that are established and taken into account.

This paper outlines the nature of the measuring equipment used in the investigation of tire-road interactions and presents the results of a study of the interfacial stress distributions of a radial-ply, a bias-belted, and a 4-ply bias-angle tire. There is a discussion of tractive ratios and effective coefficients of friction. Distributions of tractive ratios are displayed for all of the conditions treated and for the three types of tires. The paper also covers the changes in stress distributions that result from steering and the relation of these alterations to the lateral thrust and self-aligning torque of the tires.

Disturbances transmitted to the occupants of vehicles often involve tires in their formation or transmission. Tire engineers attempting to reduce disturbances in specific vehicles have two courses of action; alter the tire design according to insight or whim until subjective testing indicates improvements; or analyze the chain of relationships from sensory impression through the tire-vehicle system to internal tire design. This paper describes a “chain-of-relationships” procedure using sensory comparison techniques for identifying pertinent physical stimuli, and an approach to system modeling that best identifies structural tire properties.

The objective of the investigation is to provide a basis for judging whether or not the dynamic steering adjustments of the tire forces affect vehicle performance in a significant manner. The differential equation of cornering force adjustment is developed from experimental data. This equation is applied, for a typical radial ply tire, to a crude but sufficient mathematical model of a vehicle. The responses of the vehicle in certain maneuvers differ to some degree when the model is programmed with instantaneously reacting tires or with simulations of actual tires. The authors judge that there are slight and unimportant effects on the path and heading curves of the vehicle due to the delays in build-up cornering force. On the other hand, there appear to be detectable effects that may be important in the sensory information provided to the driver.

The paper treats the following: a. The basic mechanical processes leading to the formation of the rolling resistance of radial ply pneumatic tires, b. Special testing procedures for elucidating the contributions and characteristics of these mechanical processes, c. An assessment of the relative contributions to the rolling resistance from various mechanisms and parts of the tire.