BMW G 650 Xmoto, Manual

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Brake system with
BMW Motorrad ABS
OE
How does ABS work?
The amount of braking force that
can be transferred to the road
depends on factors hat include
the coefficient of friction of the
road surface. Loose stones, ice
and snow or a wet road all have
much lower coefficients of fric-
tion than a clean, 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 maxim-
um transferrable 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 transferrable 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 irregularit-
ies can cause the wheels to lose
contact temporarily with the road
surface; if this happens the brak-
ing force that can be transmit-
ted 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 maintained when the wheels
regain contact with the road sur-
face. At this instant the BMW
Motorrad ABS must assume an
extremely low coefficient of fric-
tion, so that the wheels will con-
tinue to rotate under all imagin-
able circumstances, because this
is the precondition for ensuring
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
Even under severe braking, a
high level of tyre 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.
Severe braking can cause
the rear wheel to lift off the
ground.
When you brake, bear in mind
that ABS control cannot be relied
on in all circumstances to prevent
the rear wheel from lifting clear of
the ground.
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z Engineering details