CROSS CASTER
Cross caster is the difference between left and
right caster.
TOE
Toe is the inward or outward angle of the wheels
as viewed from above the vehicle (Fig. 3).
• Toe-in is produced when the front edges of the
wheels on the same axle are closer together than the
rear edges.
• Toe-out is produced when the front edges of the
wheels on the same axle are farther apart than the
rear edges.
Toe-in and toe-out can occur at the front wheels
and the rear wheels.
Toe is measured in degrees or inches. The mea-
surement identifies the amount that the front of the
wheels point inward (toe-in) or outward (toe-out). Toe
is measured at the spindle height. Zero toe means
the front and rear edges of the wheels on the same
axle are equally distant.
TOE-OUT ON TURNS
Toe-out on turns is the relative positioning of the
front wheels while steering through a turn (Fig. 4).
This compensates for each front wheel’s turning
radius. As the vehicle encounters a turn, the out-
board wheel must travel in a larger radius circle
than the inboard wheel. The steering system is
designed to make each wheel follow its particular
radius circle. To accomplish this, the front wheels
must progressively toe outward as the steering is
turned from center. This eliminates tire scrubbing
and undue tire wear when steering a vehicle through
a turn.
DYNAMIC TOE PATTERN
Dynamic toe pattern is the inward and outward toe
movement of the front and rear tires through the
suspension’s jounce and rebound travel. As the vehi-
cle’s suspension moves up and down, the toe pattern
varies. Toe pattern is critical in controlling the direc-
tional stability of the vehicle while in motion. Front
and rear dynamic toe pattern is preset by the factory
at the time the vehicle is assembled.
It is not necessary to check or adjust front or rear
dynamic toe pattern when doing a normal wheel
alignment. The only time dynamic toe pattern needs
to be checked or adjusted is if the frame of the vehi-
cle has been damaged.
STEERING AXIS INCLINATION (S.A.I.)
Steering axis inclination is the angle between a
true vertical line starting at the center of the tire at
the road contact point and a line drawn through the
Fig. 3 Toe
1 - TOE-IN
2 - TOE-OUT
Fig. 4 Toe-Out On Turns
1 - TOE-OUT ON TURNS
ZB WHEEL ALIGNMENT 2 - 57
WHEEL ALIGNMENT (Continued)
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