How Does Abs Work?; What Are The Effects Of Surface Irregularities?; General Notes; Antilock Brake System (Abs) - BMW F 750 GS Rider's Manual

174 ENGINEERING DETAILS

GENERAL NOTES

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eering go to:
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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 fric-
tion of the road surface. Loose
stones, ice and snow or a wet
road all have much lower coef-
ficients of friction than a clean,
dry asphalt surface. The lower
the coefficient of friction, the
longer the stopping distance.
If the rider increases braking
pressure to the extent that
braking 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 irregu-
larities can cause the wheels
to lose contact temporarily
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 maintained when
the wheels regain contact
with the road surface. At this
instant 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 imaginable
circumstances, because this is
the precondition for ensuring
directional stability. As soon
as is registers the actual
circumstances, the system
reacts instantly and adjusts
braking force accordingly to
achieve optimum braking.