Vehicle Alignment
Safe and comfortable driving requires correct
vehicle alignment. In addition to affecting safety,
improperly aligned vehicles contribute to increased
wear and tear. This is particularly evident in
increased and uneven wear on tires. The three
primary vehicle alignment parameters are camber,
toe, and caster (Figure 13).
VISUAL INSPECTION CAPABILITIES AND
LIMITATIONS
A well-trained auto mechanic using simple tools
(Figure 14) can align a vehicle using visual methods.
Following is a typical checklist used for visual
inspection for alignment.
1. Prepare the vehicle. Ensure the vehicle is parked
on a level surface. Check that the tire pressure
aligns with the manufacturer’s specifications.
Make sure there are no heavy items in the trunk
or elsewhere that could impact the vehicle’s
stance. The vehicle should be in a neutral
position, with the steering wheel centered.
2. Inspect the tire condition. Look for signs of
uneven tire wear. Uneven wear on the inside or
outside of the tires may indicate misalignment.
3. Check the wheel toe alignment. The “toe” refers
to the angle of the wheels relative to the vehicle’s
centerline. Stand in front of the vehicle and look
at the front wheels. They should appear parallel
to each other and aligned with the car’s body.
Repeat the process from behind the vehicle,
checking the rear wheels.
4. Examine the camber angle. The camber is the
tilt of the wheel. When looking at the vehicle
from the front or back, the wheels should be
perpendicular to the ground. A visible tilt inward
(negative camber) or outward (positive camber)
could indicate a problem.
5. Observe the steering wheel position. Sit in the
driver’s seat and check if the steering wheel is
centered when the wheels are pointed straight
ahead. A misaligned steering wheel while driving
straight can indicate alignment issues.
6. Check the suspension components. Inspect the
suspension components for any signs of wear or
damage. Worn parts can affect wheel alignment.
Accurate measurements of toe and camber can
be achieved by establishing reference points
using string and a straight pipe (Figure 14). Key
alignment parameters can be measured using
these reference points, a tape measure, and a
level. While the cost of the alignment tools is
minimal, the procedure largely relies on visual
inspection and requires a well-trained mechanic.
CURRENT MACHINE VISION CAPABILITIES AND
OPPORTUNITIES
Currently, there is a shortage of well-trained
mechanics, and frequent turnover at automobile
service and repair shops increases training costs
while diminishing the productivity of mechanics
employed by these businesses. For automobile
service and repair shops specializing in vehicle
alignment, tools are required to enable mechanics
with minimal training to perform the complex task
of aligning a vehicle. Machine vision–based tools
(Figure 15) automate the vehicle alignment process
and generate digital records.
Using machine vision-based alignment tools
eliminates the error associated with visual inspec-
tion. The standard deviation for a typical machine
Figure 14. Visual
alignment of a
vehicle.
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vision–based system, for toe and camber measure-
ments, is typically around 0.02 degrees. Achieving
this level of accuracy through purely visual inspec-
tion is extremely challenging. Additionally, because
the workflow is embedded in software, technician
training requirements are reduced. The process is
guided by the software, ensuring accurate results.
Figure 16 shows results from a commercially
available machine vision–based wheel alignment
system.
A machine vision–based wheel alignment
system calculates the orientation of the wheels by
analyzing the alignment markers attached to each
wheel. Typical results, along with the acceptable
range for the specific vehicle under test, are shown
in Figure 16. For instance, the camber specification
includes a minimum of –1.75, a maximum of –0.25,
and a preferred value of –1.00 (all values are in
degrees).
Conclusion
For many years, automotive mechanics have relied
on visual inspection to perform a variety of tasks,
including tire inspection, dent repair, and wheel
alignment. Visual inspection is crucial for determin-
ing whether tires need to be replaced, identifying
and repairing dents and other damages in collision
shops, and assessing vehicle alignment by auto
mechanics. However, purely visual methods are sus-
ceptible to errors. Limitations in visual acuity, inad-
equate lighting, fatigue, and other human factors
contribute to errors in visual inspections. These
errors can range from minor, such as overlooking a
small dent, to major, such as inaccurately assessing
vehicle wheel alignment or tire tread depth.
Machine vision–based methods establish
standard inspection and repair processes, mitigate
measurement errors, reduce training require-
ments, and improve the overall efficiency of
vehicle inspections and repairs. Today, automotive
shops have access to a variety of machine vision–
based tools. These tools include both 2D and 3D
imaging for almost all aspects of vehicle inspec-
tion and repair that were previously done through
purely visual techniques. As vehicle manufacturers
continue to integrate advanced technologies into
automobiles, the demand for advanced machine
vision–based tools will increase. For instance, new
tools are required to meet the need for calibration
and repair of ADAS (Advanced Driver Assistance
Systems) and other autonomous or semi-autonomous
technologies.
AUTHOR
Daniel L. Lau, PhD: Databeam Professor and Certi-
fied Professional Engineer, Department of Electrical and
Computer Engineering, University of Kentucky, Lexington,
KY dllau@uky.edu
CITATION
Materials Evaluation 82 (7): 24–32
https://doi.org/10.32548/2024.me-04447
©2024 American Society for Nondestructive Testing
• Camera systems acquire
images of targets that
are attached to the vehicle
wheels
• A rotating turntable under
the steering wheel facilitates
castor measurements
Typical camera
systems for acquiring
images of targets
Typical camera systems for
acquiring images of targets
• Camera systems acquire images of targets that
are attached to the vehicle wheels
• A rotating turntable under the steering wheel
facilitates castor measurements
Figure 15. Tools
for performing a
machine vision–
based alignment
of a passenger
vehicle.
min –1.75
pref –1.00
max –0.25
min 0.00
pref 0.10
max 0.20
min –1.55
pref –0.80
max –0.05
min –0.03
pref 0.13
max 0.28
min –1.75
pref –1.00
max –0.25
min 0.00
pref 0.10
max 0.20
min –1.55
pref –0.80
max –0.05
min –0.03
pref 0.13
max 0.28
Rear Front
Camber –1.05
Toe 0.15
Camber –0.80
Toe 0.15
Camber –2.30
Toe –0.25
Camber –1.65
Toe –0.25
min – – –
pref – – –
max – – –
min – – –
pref – – –
max – – –
Caster 3.35 Caster 3.25
Adjust assistance
–0.05 0.25 0.55
Total toe
–0.10
–0.05 0.25 0.55
Total toe
–0.10
–0.30 0.0 0.30
Thrust angle 0.20
Figure 16. Typical
measurement results from
a machine vision–based
wheel alignment system.
FEATURE
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AUTOMOTIVEVT
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