PART 7: STARTING & OPERATING THE VEHICLE
ANTI-LOCK BRAKING SYSTEM OPERATING INFORMATION
(05/10)
Y53-6032
– 113 –
Yaw Stability
Yaw stability counteracts the tendency of a vehicle to spin
about its vertical axis. During operation, if the friction
between the road surface and the tires is not sufficient to
oppose lateral (side) forces, one or more of the tires can
slide, causing the truck/tractor to spin.
These yaw events are referred to as either “under-steer”
(where there is a lack of vehicle response to steering input
due to tire slide on the steer axle) or “over-steer” (where
the tractor's rear end slides out due to tire slide on the rear
axle) situation. Generally, shorter wheelbase vehicles
(tractors, for instance) have less natural yaw stability,
while longer wheelbase vehicles (straight trucks, for
instance) have greater natural yaw stability. Factors that
influence yaw stability are: wheelbase, suspension, steer-
ing geometry, weight distribution front to rear, and vehicle
track width.
Yaw Control
Yaw Control responds to a wide range of low- to high-fric-
tion surface scenarios including rollover, jackknife and
loss of control. In the case of vehicle slide (over-steer or
understeer situations), the system will reduce the throttle
and then brake one or more of the “four corners” of the
vehicle (in addition to potentially applying the trailer
brakes), thus applying a counter-force to better align the
vehicle with an appropriate path of travel. For example, in
an over-steer situation, the system applies the “outside”
front brake; while in an under-steer condition, the “inside”
rear brake is applied.
Y53-6032.book Page 113 Monday, May 24, 2010 3:37 PM
Summary of Contents for Peterbilt 587
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