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129n
Index Data Technology Repairs Car care Controls Overview
Antilock Brake System (ABS)
The concept
ABS enhances active safety by helping
to prevent the wheels from locking dur-
ing brake applications. The reason:
Locked wheels are dangerous. When
the front wheels slide, the driver loses
steering control over the vehicle. Trac-
tion loss at the rear wheels can cause
the rear end to break into an uncon-
trolled skid.
With ABS, you will achieve the shortest-
possible braking distances under all
given conditions (braking while driving
straight ahead or in curves, different
road surfaces).
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
pavement, snow, ice).
Braking with ABS
The system becomes operative once
the vehicle exceeds a speed of approx.
6 mph (10 km/h). The ABS is deactivated
whenever the vehicle's speed drops
back below approx. 4 mph (6 km/h). This
means that the wheels can lock in the fi-
nal phase of a panic stop – a factor of no
significance in actual use.
If you are in a situation that requires full
braking, you will exploit the full benefits
of the ABS system if you apply maximum
brake pressure ("panic stop"). Since the
vehicle maintains steering responsive-
ness, you can avoid possible obstacles
with a minimum of steering effort, de-
spite the full brake application.
The ABS system's closed-loop control
circuit cycles in fractions of a second.
A pulsation at the brake pedal, together
with the sounds associated with the
hydraulic controls, tells you that the
brake system is within its maximum
limit range and reminds you that you
should adapt road speed to the road
conditions.
On road surfaces that have a loose
surface layer on a firm base with good
traction (on gravel or snow, for in-
stance), braking distances may be
longer than with locked wheels. This is
also true if snow chains are mounted.
However, ABS continues to provide
enhanced vehicle stability and steering
response under these conditions.
Online Edition for Part No. 01 41 0 004 597 - © 08/99 BMW AG
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