Antilock Brake System (Abs) - BMW 528I Owner's Manual

Antilock Brake System (ABS)

The concept
ABS enhances active safety by helping
to prevent the wheels from locking un-
der braking. The reason: 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 end to
break into an uncontrolled skid.
ABS is designed to meet two essential
requirements during every brake appli-
cation:
> To help provide vehicle stability
> To help retain steering and maneu-
vering capability on all types of road
surface (asphalt, cement, dirt, mois-
ture, snow and ice).
The system can achieve the shortest
braking distances possible under most
conditions (on straight-away 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.
6 mph (10 km/h). The ABS is deacti-
vated whenever the vehicle's speed
drops back below approx. 4 mph
(6 km/h). This means that the wheels
can lock in the final phase of a brake
application – a factor of no significance
in actual use.
If you are in a situation which requires
full braking, you will exploit the full ben-
efits of the ABS system if you apply
maximum 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 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, the audible
pulsation that accompanies the control
operation calls the attention of the
driver to the reduced traction between
the tires and the road surface (slippery
road surface), and serves as a reminder
that the speed of the car should be re-
duced to adapt to road conditions.
On road surfaces which have a loose
layer on a firm base (on gravel or snow,
for instance), the braking distances with
ABS may be longer than with the
wheels locked. The same applies when
snow chains have been mounted. How-
ever, ABS continues to provide en-
hanced vehicle stability and steering re-
sponse under these conditions.
Online Edition for Part No. 01 41 0 155 012 - © 07/99 BMW AG
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