Yamaha FJR1300A(X), Service Manual, Page: 16 / 754

FEATURES
1-7
• Slip ratio:
When the brakes are applied, slipping occurs between the tires and the road surface. This causes a
difference between the wheel speed and the chassis speed.
Slip ratio is the value that shows the rate of wheel slippage and is defined by the following formula.
0%: There is no slipping 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).
Brake force and vehicle stability
When the brake pressure is increased, wheel speed is reduced. Slipping 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.
Side force is also closely related to wheel slippage. See figure “A”. If the brakes are applied while keep-
ing the proper slip ratio, it is possible to obtain the maximum brake force without losing much side force.
ABS allows full use of the tires’ capabilities even on slippery road surfaces or less slippery road surfac-
es. See figure “B”.
Wheel slip and hydraulic control
The ABS ECU calculates the wheel speed of each wheel according to the rotation signal received from
the front and rear wheel sensors. In addition, the ABS ECU calculates the vehicle chassis speed and
the rate of speed reduction based on the wheel speed values.
Slip ratio =
Chassis speed –
Wheel speed
×
100 (%)
Chassis speed
b
c
a
A
d
a
e
f
g
d
B
a. Friction force between the tire and road
surface
b. Brake force
c. Side force
d. Slip ratio (%)
e. Less slippery road surface
f.
Controlling zone
g. Slippery road surface