BMW HP4 Rider's Manual page 113

What happens when
rough roads are
encountered?
Bumpy or rough roads can briefly
lead to a loss of contact be-
tween the tires and the road sur-
face, until the transferable brak-
ing force is reduced to zero. If
braking is carried out in this sit-
uation, ABS must reduce the
brake pressure to ensure driv-
ing stability when restoring con-
tact to the road. At this point in
time, the BMW Motorrad Integral
ABS must assume extremely low
friction coefficients (gravel, ice,
snow) so that the running wheels
turn in every imaginable case and
the driving stability is ensured.
After detecting the actual con-
ditions, the system adjusts the
optimum brake pressure.
How is the BMW Motorrad
Race ABS noticeable to
the rider?
If the ABS system must reduce
the braking forces due to the
conditions described above, then
vibrations can be felt at the hand-
brake lever.
If the handbrake lever is pulled,
then braking pressure is built up
at the rear wheel with the integral
function. If the footbrake lever is
first actuated after this, the brake
pressure already built up can be
felt earlier than the counter-pres-
sure, than when the footbrake
lever is actuated before or to-
gether with the handbrake lever.
Lifting off rear wheel
Even during severe braking, a
high level of tire grip can mean
that the front wheel does not
lock up until very late, if at all.
Consequently, ABS does not in-
tervene until very late, if at all.
Under these circumstances the
rear wheel can lift off the ground,
and the outcome can be a high-
siding situation in which the mo-
torcycle can flip over.
Heavy braking can lead to
the rear wheel lifting off the
ground.
When braking, bear in mind
that the ABS control cannot
always be relied on to prevent
the rear wheel from lifting off the
ground.
Special situations
To detect the tendency of the
wheels to lock up, the speeds
of the front and rear wheel are
compared. If implausible values
are detected over a longer period
of time, the ABS function is de-
activated for safety reasons and
an ABS fault is indicated. The
condition for a fault code is the
completed self-diagnosis.
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