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Antilock Brake System (ABS)
The concept
ABS enhances active safety by helping
to prevent the wheels from locking when
the brakes are applied. This is done be-
cause locked wheels are dangerous.
When the front wheels slide, the driver
loses steering control over the vehicle.
Traction loss at the rear wheels can
cause the rear axle to break into an un-
controlled skid.
ABS is designed to meet two essential
requirements during every brake appli-
cation:
> to help provide vehicle stability
> to help maintain steering control and
maneuverability – on all types of road
surfaces (asphalt, concrete, mud,
wet, snow, ice).
The system can achieve the shortest
braking distances possible under most
conditions (on straight-aways and in
curves, on asphalt, ice, wet road sur-
faces, etc.).
Braking with ABS
The system becomes operative once
the vehicle exceeds a speed of approx.
5 mph (8 km/h). The ABS is deactivated
whenever the vehicle's speed drops
back below approx. 2 mph (3 km/h).
This means that the wheels can lock in
the final phase of a brake application –
a factor of no significance in actual
practice.
If you are in a situation that requires full
braking, you will exploit the full benefits
of the ABS system if you apply maxi-
mum brake pressure ("panic stop").
Since the vehicle maintains steering re-
sponsiveness, you can avoid possible
obstacles with a minimum of steering
effort, despite the full brake application.
The ABS system's closed-loop control
circuit cycles in fractions of a second.
A pulsation at the brake pedal indicates
to the driver that ABS is active, that is,
that the vehicle is within its maximum
braking range. In addition, a pulsation –
a result of the control function cycles –
indicates to the driver that vehicle
speed should be reduced to adapt to
road surface conditions when there is
reduced traction and grip between tires
and road surface (slippery road sur-
face).
Always depress the brake pedal steadily
and with consistent application force.
Do not pump the brakes.
On road surfaces that have a loose sur-
face layer on a firm base with good
traction (on gravel or snow, for exam-
ple), or when driving with snow chains,
braking distances may be longer than
with locked wheels. However, ABS
continues to provide enhanced vehicle
stability and steering response under
these conditions.
Online Edition Part-No. 01 41 0 155 062 - © 07/99 BMW AG