BMW 2010 650 Service Manual download pdf (Page 57)

Brake system with

BMW Motorrad ABS

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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Engineering details

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