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 vehicle’s suspension moves up and down, the toe pattern varies. Toe pattern is
critical in controlling the directional 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 vehicle has been damaged.
STEERING AXIS INCLINATION (S.A.I.)
Steering axis inclination (1) 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 center
of the upper ball joint (or strut) and the lower ball joint.
S.A.I. is built into the vehicle and is not an adjustable
angle. If S.A.I. is not within specifications, a bent or
damaged suspension component may be the cause.
INCLUDED ANGLE (I.A.)
Included angle (3) is the sum of the S.A.I. angle (1)
plus or minus the camber angle (2), depending on
whether or not the wheel has positive or negative
camber. If camber is positive, add the camber angle to
the S.A.I angle. If camber is negative, subtract the
camber angle from the S.A.I. angle. Included angle is
not adjustable, but can be used to diagnose a frame
misalignment or bent suspension component (spindle,
strut).
THRUST ANGLE
Thrust angle is the averaged direction the rear wheels
are pointing in relation to the vehicle’s center line. The
presence of negative or positive thrust angle causes
the rear tires to track improperly to the left or right of
the front tires (dog tracking).
•
Negative thrust angle means the rear tires are
tracking to the left of the front tires.
•
Positive thrust angle means the rear tires are
tracking to the right of the front tires.
Improper tracking can cause undue tire wear, a lead
or pull and a crooked steering wheel. Excessive thrust
angle can usually be corrected by adjusting the rear
wheel toe so that each wheel has one-half of the total
toe measurement.
PM
WHEEL ALIGNMENT
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