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General notes
8
To find out more about engineer-
ing go to:
142
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logy
Antilock 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
z
much lower coefficients of friction
than a clean, dry asphalt surface.
The lower the coefficient of fric-
tion, the longer the stopping 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 motorcycle loses
its directional stability; a fall is
imminent. 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 (gravel, ice,
snow), so that the wheels will
continue to rotate under all ima-
ginable circumstances, because
this is the precondition for ensur-
ing directional stability. As soon
as is registers the actual circum-
stances, the system reacts in-
stantly and adjusts braking force
accordingly to achieve optimum
braking.
Rear wheel lift
Under very severe and sudden
deceleration, however, under
certain circumstances it is pos-
sible that the BMW Motorrad
ABS will be unable to prevent
the rear wheel from lifting clear
of the ground. If this happens
the outcome can be a highsiding
situation in which the motorcycle
can flip over.
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