General Instructions; Anti-Lock Brake System; (Abs); Anti-Lock Brake System (Abs) - BMW F800GT Rider's Manual

General instructions

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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
z
than a clean and dry asphalt sur-
face. The lower the coefficient
of friction, the longer the braking
distance.
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. The wheels continue to
turn and the driving stability is
retained irrespective of the road
condition.
What are the effects of
surface irregularities?
Surface irregularities can cause
the wheels to lose contact tem-
porarily with the road surface. If
this happens the braking force
that can be transmitted to the
road can drop to zero. If the
brakes are applied under these
circumstances the ABS has to
reduce braking force to ensure
that directional stability is main-
tained when the wheels regain
contact with the road surface.
At this instant the ABS must
assume an extremely low coef-
ficient 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 it registers the actual
circumstances, the system re-
acts instantly and adjusts braking
force accordingly to achieve op-
timum braking.
Rear wheel lift
Under very severe and sudden
deceleration, however, it is pos-
sible that the 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.