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WHAT CASTER DOES
A positive caster will aid in steering wheel return to a straight
ahead position. This is typically noticed following turns.
POSITIVE CASTER
If the angle is excessive (positive) steering will feel stiff
going into turns typically on vehicles without power steering.
NEGATIVE CASTER
Negative caster will allow turning into corners easier while
the vehicle is moving forward, however excessive nega-
tive caster will make the vehicle wander or cause it to be
unstable at speed while driving straight ahead.
ADJUSTMENT METHOD
Strut Rod, Shims, Cams, Slotted Frame, Strut Rotation,
Wedges, Ball Joint Rotation, Offset Ball Joints.
Toe us a design specification indicated by manufacturers to
achieve a "running toe condition" which provides directional
stability, low rolling resistance and optimum tire life.
MEASUREMENT METHOD
If dimension "B" is greater than dimension "A", the vehicle is
defined to have "Toe In".
Toe can be measured both as an angle or by the difference
between the "A" and "B" measurement. Though the method
of measurement differs depending on regions and vehicle
manufacturer's specifications, it is becoming increasingly
common to measure toe as an angle.
WHAT TOE DOES
If "A" is greater than "B", the vehicle has negative toe or
"Toe Out". On rear wheel drive vehicles, the front wheels are
being pushed along the road, and normal road drag will act
to separate the front edges of the front wheels as the play
in the front end is taken up.
These rear wheel drive vehicles typically require some
amount of toe in, such that when drag acts to separate the
front wheels, the front ends track at zero toe. This assumes
a typical positive scrub radius.
TOE
On most front wheel drive vehicles, the torque on the front
wheels acts to pull the front edges of the front wheels
together (when a positive scrub radius exists). In this situa-
tion, some toe out will allow the front wheels to track at zero
toe. However, not all front wheel drive vehicles require toe
out, and the manufacturer's specifications must always be
checked before any adjustments are made. This is due to
varying scrub angles which affect the toe dynamics while
the vehicle is driving down the road.
EXCESSIVE TOE
Toe is a common tire wearing angle. Excessive toe either
in or out will cause tire wear and unstable operation. When
the toe is extreme the vehicle will typically go in the direction
of the most loaded tire (or the one with the most traction),
meaning that as the vehicle goes over bumps it will dart
from one side to the other. This can also be due to bump
steer which is a different condition. Bump Steer is caused
when the toe angle changes as the vehicle suspension com-
presses expands.
ADJUSTMENT METHOD
Almost all vehicles use some form of Tie Rod Adjuster.
When toe is measured it represents the difference between
dimension "A" and "B. Dimension "A" is the distance from
the extreme front edge (centerline) of the left tire to the
extreme front edge of the right tire. Dimension "B" is the
distance from the extreme rear edge (centerline) of the left
tire to the extreme rear edge of the right tire. The toe present
on the vehicle is then (B - A). Toe measurements are read
as an angular measurement.
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