A vehicle motion control apparatus is provided for performing a vehicle
stability control on the basis of a parameter indicative of lateral
margin for a tire on a road. The apparatus includes a steering control
device for controlling a relationship between a steering angle and a tire
angle to be varied, and a decelerating control device for controlling a
vehicle speed to be decreased. The parameter indicative of lateral margin
for the tire is monitored, and the steering control device and the
decelerating control device are controlled on the basis of the monitored
parameter. The steering control device is controlled to decrease the tire
angle relative to the steering angle, when the parameter is decreased
from a value of relatively large lateral margin to a value of relatively
small lateral margin, which is smaller than a first threshold value, and
the decelerating control device is controlled to decrease the vehicle
speed in addition to the steering control by the steering control device,
when the parameter is further decreased to a value of lateral margin
smaller than a second threshold value, which is smaller than the first
threshold value.