A robust nonparametric approach to improve vehicle yaw rate dynamics by means of a rear active differential is introduced. An additive model set is used to describe the uncertainty arising from the wide range of the vehicle operating situations. The effects of saturation of the control variable (i.e. yaw moment) have been taken into account by adopting enhanced internal model control methodologies in the design of the feedback controller. In order to improve the transient behavior a feedforward control contribution has been added giving rise to a two degree of freedom structure. Improvements on understeering characteristics, stability in demanding conditions such as mu-split braking and damping properties in impulsive maneuvers are shown through simulation results performed on an accurate 14 degree of freedom nonlinear model