A wheel alignment adjusts the suspension and steering angles to ensure proper vehicle handling and minimize tire wear. The key alignment angles are camber, caster, toe, steering axis inclination, and included angle. Camber is the tilt of the wheel from vertical. Caster is the tilt of the steering axis. Toe is the difference in width between the front and rear of the tires. Correct alignment reduces tire wear and keeps the vehicle traveling in a straight line.

1. TOPIC 9:
WHEEL ALIGNMENT

3. OBJECTIVES:
Explain how camber, caster, and toe affect the handling and tire
wear of the vehicle.
A wheel alignment is the adjustment of the suspension and
steering to ensure proper vehicle handling with minimum tire
wear.
When a vehicle is new, the alignment angles are set at the factory.
After many miles and/or months of driving, the alignment angles
can change slightly.
By adjusting the suspension and steering components, proper
alignment angles can be restored. An alignment includes checking
and adjusting, if necessary, both
front and rear wheels.

4. A pull is usually defined as a tug on the steering wheel toward one
side or the other.
ALIGNMENT-RELATED PROBLEMS
Most alignment diagnosis is symptom-based diagnosis. The
problem with the alignment is determined from symptoms such
as excessive tire wear or a pull to one side of the road.
Pull Defined as a definite tug on the steering wheel or pull
toward the left or the right while driving straight on a level road.
Bent, damaged, worn
suspension and/or steering
components or tire problems
can cause this.

5. Road Crown Effects Most roads are constructed with a slight
angle to permit water to drain from the road surface. On a two-lane
road, the center of the road is often higher than the berms, resulting
in a road crown.
The crown of the road refers to the angle or slope of the roadway needed to drain water
off the pavement.

6. Wander is an unstable condition requiring constant driver corrections.
Wander A condition where constant steering wheel corrections
are necessary to maintain a straight-ahead direction on a straight,
level road is called wander.
Worn suspension and/or steering components are the likely cause of
this condition. Incorrect or unequal alignment angles such as caster
and toe, as well as defective tire(s), can cause this condition.

7. Positive camber. The solid vertical
line represents true vertical; the
dotted line the angle of the tire.
Negative camber. The solid vertical
line represents true vertical; the
dotted line the angle of the tire.
Zero camber.
Note the angle
of the tire is true
vertical.
CAMBER
Camber: is the inward or outward tilt of the wheels from true vertical as viewed from the
front or rear of the vehicle.

8. included angle causes scuffing and wear on the
outside edge of the tire

9. Excessive negative camber
causes scuffing and wear on the inside edge of the
tire,

10. Positive camber applies the vehicle weight
toward the larger inner wheel bearing. This is
desirable because the larger inner bearing is
designed to carry more vehicle weight than the
outer bearing.
Negative camber applies the vehicle weight to the
smaller outer wheel bearing. Excessive negative
camber, may contribute to outer wheel bearing
failure.
Incorrect camber can cause excessive wear on wheel bearings.
Many vehicle manufacturers specify positive camber so the vehicle’s weight is applied
to the larger inner wheel bearing and spindle.

11. Caster:
is the forward or rearward tilt of the steering axis in reference to a vertical line as viewed
from the side of the vehicle.
Zero caster.
The steering axis is defined
as the line drawn through
the upper and lower steering
pivot points.
Zero caster means the steering
axis is straight up and down.

12. Positive (+) caster Negative (–) caster is seldom specified
on today’s vehicles because it tends to
make the vehicle unstable at highway
speeds. Negative caster was specified
on some older vehicles not equipped
with power steering to help reduce the
steering effort.
Caster

13. Toe
Toe is the difference in distance between the front and rear of the tires.
As viewed from the top of the vehicle (a bird’s eye view), zero toe
means that both wheels on the same axle are parallel, as shown:
Zero toe. Note how both
tires are parallel to each
other as viewed from
above the vehicle.

14. Total toe is often expressed as an angle. Because both front wheels are tied together through
the tie rods and center link, the toe angle is always equally split between the two front wheels
when the vehicle moves forward.
Toe is also described as a comparison of horizontal lines drawn
through both wheels on the same axle, as shown here.

15. If the front of the tires is closer than the rear of the same tires,
then the toe is called toe-in or positive (+) toe.
Toe-in, also called positive (+) toe.

16. Some manufacturers of front-wheel-drive vehicles specify a toe-out
setting to compensate for the toe-in forces created by the engine
drive forces on the front wheels.
If the front of the tires is farther apart than the rear of the same
tires, then the wheels are toed-out, or have negative (–) toe.
Toe-out, also called negative (–) toe.

17. The purpose of correct toe setting is to provide maximum stability
with a minimum of tire wear when the vehicle is being driven.
Continued
Incorrect toe is the major
cause of excessive tire
wear!
This tire is just one month old! It was new and installed
on the front of a vehicle that had about 1/4 inch (6 mm)
of toe-out. By the time the customer returned to the tire
store for an alignment, the tire was completely bald on
the inside. Note the almost new tread on the outside.

18. NOTE: If the toe is improper by just 1/8 in. (3 mm), the resulting tire
wear is equivalent to dragging a tire sideways 28 feet (8.5 m) for
every mile traveled (1.6 km).
If not correct, toe causes camber-type wear on one side of the tire.
Excessive toe-out and the type of wear that can occur to the inside of the left front tire.

19. Feather-edge wear is also common,
especially if the vehicle is equipped
with nonradial tires.
Excessive toe-in and the type of wear that can
occur to the outside of the left front tire.
Feather-edge wear pattern
caused by excessive toe-in
or toe-out.

20. Rear toe-in (+). The rear toe (unlike the front toe)
can be different for each wheel while the vehicle
is moving forward because the rear wheels are
not tied together as they are in the front.
Diagonal wear such as shown here is
usually caused by incorrect toe on the
rear of a front-wheel-drive vehicle.
Incorrect toe can
cause the tire to
run sideways as it
rolls, resulting in a
diagonal wipe.

21. STEERING AXIS INCLINATION (SAI)
The steering axis is the angle formed between true vertical and an
imaginary line drawn between the upper and lower pivot points of
the spindle.
Steering axis inclination (SAI) is the inward tilt of the steering
axis. SAI is also known as kingpin inclination (KPI) and is the
imaginary line drawn through the kingpin as viewed from the
front.
SAI is also called ball joint inclination (BJI), if SLA-type
suspension is used, or MacPherson strut inclination (MSI).
Continued

22. The left illustration shows that the
steering axis inclination angle is
determined by drawing a line through the
center of the upper and lower ball joints.
This represents the pivot points of the
front wheels when the steering wheel is
rotated during cornering.
The right illustration shows that the
steering axis inclination angle is
determined by drawing a line through
the axis of the upper strut bearing
mount assembly and the lower ball
joint.
STEERING AXIS INCLINATION (SAI)

23. INCLUDED ANGLE
The included angle is the SAI added
to the camber reading of the front
wheels only.
Included angle on a MacPherson-strut-type
suspension.
The included angle is determined by
the design of the steering knuckle,
or strut construction.

24. Included angle is an important angle to measure for diagnosis of
vehicle handling or tire wear problems. If the cradle is out of
location due to previous service work or an accident, knowing
SAI, camber, and included angle can help in determining what
needs to be done to correct the problem.
Cradle placement. If the cradle is not replaced in
the exact position after removal for a
transmission or clutch replacement, the SAI,
camber, and included angle will not be equal
side-to-side.
If the included angles are equal
side-to-side, but the camber is
unequal on both sides, the SAI
must be unequal.
For best handling, the included
angle should be within 1/2
degree of the SAI of the other
side of the vehicle.

25. TURNING RADIUS (TOE-OUT ON TURNS)
When a vehicle turns a corner, the inside wheel has to turn at a sharper
angle than the outside wheel because the inside wheel has a shorter
distance to travel.
To provide handling, the inside wheel has to turn
at a greater turning radius than the outside
wheel.
1. Tire squeal noise during
normal cornering, even at
low speeds
2. Scuffed tire wear
Turning radius, a nonadjustable angle, is called toe-out on turns, TOT or
TOOT.
Symptoms of out-of-spec
turning angle include:
It is determined by angle of the steering knuckle arms, and should be
measured to check if the steering arms are bent or damaged.

26. The proper toe-out on turns is achieved by angling the steering arms.
The proper angle of the steering arms is where imaginary lines
drawn from the steering arms should intersect exactly at the center
of the rear axle. This angle is called the Ackerman Effect (named for
its promoter, English publisher, Rudolph Ackerman, ca. 1898).

27. SETBACK
Setback is the angle formed by a line drawn perpendicular (at 90
degrees) to the front axles.
(b) Negative setback.
(a)
(b)
(a) Positive setback.
Positive setback means
the right front wheel is
set back farther than
the left
negative setback means
the left front wheel is set
back farther than the
right.

28. The causes of setback include the following:
1. Cradle placement not correct on a front-wheel-drive vehicle. This can be
caused by incorrectly installing the cradle after a transmission, clutch, or
engine replacement or service.
2. An accident that affected the frame or cradle of the vehicle and was
unnoticed or not repaired
Cradle placement affects setback.

29. (a)
(b)
(c)
Zero thrust angle.
Thrust line to the right.
Thrust line to the left.
If both rear wheels have zero toe, then the thrust angle is the same as the geometric centerline of the vehicle.
The total of the rear toe setting determines the thrust line, or the direction the rear wheels are pointed.
THRUST ANGLE
On vehicles with an independent
rear suspension, if both wheels do
not have equal toe, the vehicle
will pull in the direction of the side
with the most toe-in.

30. (a)
(b)
Proper tracking.
Front wheels steering
toward thrust line.
TRACKING
The rear wheels should track directly behind the front wheels. If the vehicle has been involved in an accident, it is
possible that the frame or rear axle mounting could cause dog tracking.