WHEEL ALIGNMENT 2B – 3
STEERING AXIS INCLINATION
Steering Axis Inclination (SAI) is the tilt at the top of the
steering knuckle from the vertical. Measure the SAI
angle from the true vertical to a line through the center of
the strut and the lower ball joint as viewed from the front
of the vehicle.
SAI helps the vehicle track straight down the road and
assists the wheel back into the straight ahead position.
SAI on front wheel drive vehicles should be negative.
INCLUDED ANGLE
The included angle is the angle measured from the cam-
ber angle to the line through the center of the strut and
the lower ball joints as viewed from the front of the ve-
hicle.
The included angle is calculated in degrees Most align-
ment racks will not measure the included angle directly.
To determine the included angle, subtract the negative
or add the positive camber readings to the Steering Axis
Inclination (SAI).
SCRUB RADIUS
The scrub radius is the distance between true vertical
and the line through the center of the strut and lower ball
joint to the road surface. Scrub radius is bulit into the de-
sign of the vehicle. Scrub radius is not adjustable.
SETBACK
The setback is the distance in which one front hub and
bearing assembly may be rearward of the other front
hub and bearing assembly. Setback is primarily caused
by a road hazard or vehicle collision.
TURNING ANGLE
The turning angle is the angle of each front wheel to the
vertical when the vehicle is making a turn.