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.