General instructions
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logy
Anti-lock brake system
(ABS)
How does ABS work?
The amount of braking force that
can be transferred to the road
depends on factors that include
the coefficient of friction of the
road surface. Loose stones, ice
and snow or a wet road all have
much lower coefficients of friction
than a clean, dry asphalt surface.
The lower the coefficient of fric-
tion, the longer the braking dis-
tance.
If the rider increases braking
pressure to the extent that brak-
ing force exceeds the maximum
transferable limit, the wheels start
to lock and the vehicle loses its
directional stability; a fall is im-
minent. Before this situation
can occur, ABS intervenes and
adapts braking pressure to the
maximum transferable braking
force, so the wheels continue
to turn and directional stability
is maintained irrespective of the
condition of the road surface.
What are the effects of
surface irregularities?
Humps and surface irregular-
ities can cause the wheels to
lose contact temporarily with
the road surface; if this hap-
pens the braking force that can
be transmitted to the road can
drop to zero. If the brakes are
applied under these circum-
stances the ABS has to reduce
braking force to ensure that dir-
ectional stability is maintained
when the wheels regain contact
with the road surface. At this in-
stant the BMW Motorrad ABS
must assume an extremely low
coefficient of friction, so that the
wheels will continue to rotate un-
der all imaginable circumstances,
because this is the precondition
for ensuring directional stability.
As soon as is registers the ac-
tual circumstances, the system
reacts instantly and adjusts brak-
ing force accordingly to achieve
optimum braking.
What is the design
baseline for
BMW Motorrad ABS?
Within the limits imposed by
physics, BMW Motorrad ABS en-
sures directional stability on any
surface. The system is not op-
timised for special requirements
that apply under extreme com-
petitive situations off-road or on
the track.
8
90
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Engineering details
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