Mazda Training manual — part 82

Dynamic Driving Safety Systems

Fundamentals

•

The illustration below shows the influence of the wheel slip to the coefficient of friction
between a tire and a dry normal road.

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X Wheel slip

Y Coefficient of friction

Curriculum Training

01-7

Fundamentals

Dynamic Driving Safety Systems

Kamm’s Circle

•

A tire transmits both longitudinal and lateral forces to the road surface. Both forces form
the resulting force that must be transmitted by the tire.

•

A completely blocked wheel can no longer exert any cornering force. On the other hand,
a vehicle that is subjected to additional braking when being pushed to the limit of
adhesion during cornering will start to skid.

•

The dependence on longitudinal and lateral force is shown in the so-called “Kamm’s
circle”. As long as the resulting force remains within the illustrated circle, driving stability
of the vehicle is ensured. If the resulting force leaves the circle, the vehicle becomes
unstable and skids.

NOTE:

The diameter of the Kamm’s circle, (the maximum transmittable force) depends on

the above mentioned values.

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1 Lateral force

3 Longitudinal force

2 Resulting

force

01-8 Curriculum

Training

Dynamic Driving Safety Systems

Fundamentals

•

The illustration below shows the dependency between longitudinal and lateral force in a
diagram.

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X Slip

2 Lateral

force

Y Transmittable force

3 Stable driving condition

1 Longitudinal force

4 Instable driving condition

Curriculum Training

01-9

Fundamentals

Dynamic Driving Safety Systems

Antilock Brake System

•

Although all Mazdas are equipped with powerful and reliable brake systems that provide
excellent braking power even at high speeds, a standard brake system cannot prevent a
driver from over-reacting in an emergency situation and applying too much force to the
brake pedal (especially under bad road / weather conditions or in case of an emergency
braking).

•

If the driver applies too much force to the brake pedal, the wheels will lock-up and the
vehicle might skid, especially on irregular road surfaces.

L2003_01008

01-10 Curriculum

Training