Yamaha 2007 XP500 Service Manual page 15

FEATURES
0%: There is no slip between the wheel and the road surface. The chassis speed is equal to the wheel
speed.
100%: The wheel speed is "0", but the chassis is moving (i.e., wheel lock).
EAS15B1006
Brake force and vehicle stability
When the brake pressure is increased, wheel speed is reduced. Slip occurs between the tire and the
road surface and brake force is generated. The limit of this brake force is determined by the friction
force between the tire and the road surface and is closely related to wheel slippage. Wheel slippage is
represented by the slip ratio. Therefore, side force is also closely related to wheel slippage. See figure
"A". If the brakes are applied while keeping the proper slip ratio, it is possible to obtain the maximum
brake force without losing much side force. ABS allows full use of the tire capabilities even on slippery
road surfaces or less slippery road surfaces. See figure "B" .
EAS15B1007
Wheel slip and hydraulic control
The ECU (ABS) calculates the wheel speed of each wheel according to the rotation signal received
from the front and rear wheel sensors. In addition, the ECU (ABS) calculates the vehicle chassis speed
and the rate of speed reduction based on the wheel speed values.
The difference between the chassis speed and the wheel speed calculated in the slip ratio formula is
equal to the wheel slip. When the wheel has a tendency to lock, the wheel speed is suddenly reduced.
When the wheel slip and the wheel speed reduction rate exceed the preset values, the ECU (ABS) de-
termines that the wheel has a tendency to lock.
If the slip is large and the wheel has a tendency to lock (point A in the figure), the ECU (ABS) reduces
the brake fluid pressure in the brake caliper and increases the pressure of the brake fluid in the brake
caliper when the tendency to lock has diminished (point B in the figure).
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