TIRE SIZE AND INFLATION PRESSURE INFLUENCE ON STATIC STEERING EFFORT 2010-36-0105

The required hand wheel effort the driver inputs into the steering wheel during parking maneuvers is an important design factor for a vehicle, that has a strong influence on the customer's overall perception of steering performance. During the development of a new vehicle, the designer is faced by the challenge of achieving the desired level of steering effort without jeopardizing other handling characteristics, like steering sensitivity and on-center performance. The suspension and steering tuning to achieve the adequate trade-off between these different metrics is especially critical for manual steering systems, which is a very common configuration for emerging market vehicles. In addition, due to communization of architectures, it is common that a vehicle with a manual steering system must share common suspension components and geometric parameters with configurations that have power steering assistance, making this trade-off even more difficult.

The objective of this work is to evaluate the influence of tire size and inflation pressure on static steering effort. This was quantified by objective measurements of steering wheel torque for parking maneuvers over a surface with controlled friction coefficient, changing only the tire parameters. The interaction of these parameters with other handling metrics is a natural sequence of this work, however is not being evaluated here due time and resource restrictions. In the sequence of the physical measurements, the results obtained have been compared against analytical predictions of the static steering effort, where the tire scrub torque has been calculated using finite element models that consider all relevant parameters of the tires physically evaluated including the non-linear effects. The results of this study allowed the understanding of the tire parameters that affected the most the static steering effort within the studied range. Finally, the correlation of the analytical simulation results with the physical measurements makes it possible for both the vehicle and the tire development teams to design and specify tires that can help meeting specific static steering effort targets early in the development cycle, taking advantage of reduced time and costs associated with the usage of early virtual assessments.