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Slip
The brake slip is the difference between the vehicle speed and the wheel circumference speed. If
the wheel locks, the slip is greatest, that is 100 %. If the wheel is running freely and un-braked,
the slip is the lowest, equal to 0 %. Slip can be calculated from the vehicle speed Vveh and the
wheel speed Vw. The equation for this is:
Vveh = 100 km/h, Vw = 70 km/h
Slip ratio (S) =
S = 30%
Typical Slip Curves
Vveh - Vw
X 100%
Vveh
For the various road conditions, the friction
coefficients were plotted. The typical course
of the curves is always the same. The only
special feature is shown by the curve for
freshly fallen snow, for this curve increases at
100 % slip. In a vehicle without ABS, the
wheel locks on braking and therefore pushes
a wedge before it. This wedge of loose
surface or freshly fallen snow means and
increased resistance and as a result the
stopping distance is shorter. This reduction in
stopping distance is not possible with a
vehicle with ABS, as the wheel does not lock.
On these surfaces the stopping distance with
ABS is longer than without ABS. The reason
for this is based in physics and not in the
Anti-Lock System.
However, as mentioned before, ABS is not
about the stopping distance, but
maneuverability and driving stability, for the
vehicle with locking wheels without ABS
cannot be steered.
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