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TRN-AUTO19-04 · Lesson 10 · 30 clock hours · lab

Four-Wheel Computerized Alignment: Setup, Measurement, and Adjustment

Objective. Students will perform a complete four-wheel computerized wheel alignment on an assigned vehicle, measuring all primary angles, identifying adjustable and non-adjustable components, and making all manufacturer-approved adjustments to bring the vehicle within specification.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a certified examiner or master technician in the trade or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.

Why Four-Wheel Alignment Matters

Wheel alignment is the precise adjustment of a vehicle's suspension and steering geometry so that every tire contacts the road at the correct angle. When alignment angles fall outside manufacturer specification, the result is uneven tire wear, pulling or drifting during straight-line driving, poor fuel economy, and premature wear of steering and suspension components. A four-wheel computerized alignment measures and corrects angles at all four corners simultaneously, accounting for the relationship between the front and rear axles — something a traditional two-wheel alignment cannot do.

Primary Alignment Angles

Camber is the inward or outward tilt of the tire when viewed from the front. Positive camber means the top of the tire tilts outward; negative camber means it tilts inward. Excessive positive camber wears the outer tread edge; excessive negative camber wears the inner edge. Most passenger vehicles specify a slight negative or near-zero camber.

Toe describes whether the fronts of the tires point toward each other (toe-in) or away from each other (toe-out) when viewed from above. Toe is the most critical adjustment for tire wear. Incorrect toe causes a feathered or sawtooth tread wear pattern. Toe is typically expressed in degrees or fractions of an inch.

Caster is the forward or rearward tilt of the steering axis when viewed from the side. Positive caster (top of the steering axis tilted rearward) improves straight-line stability and steering return. Caster is measured on the front axle only. It is rarely adjustable on modern unibody vehicles, but must be verified.

Thrust angle is the direction the rear axle is pointed relative to the vehicle's centerline. A non-zero thrust angle causes a vehicle to dog-track (rear axle offset from front axle). The alignment system calculates a thrust line from rear toe readings; the front wheels are then adjusted to the thrust line, not just the geometric centerline.

Setback is a difference in the fore-aft position of one front wheel compared to the other, often indicating prior collision damage.

The Alignment System and Run-Out Compensation

Modern computerized alignment heads use electronic sensors — typically cameras, inclinometers, or a combination — to measure angles in real time. Before any measurement is trusted, run-out compensation must be performed. This procedure corrects for any wobble caused by bent rims, hub flange runout, or imperfect head mounting.

To perform run-out compensation: with the heads clipped securely to all four wheels and the vehicle on the alignment rack, roll the vehicle slowly backward a short distance (typically about 10–12 inches), stop, let the software record the position, then roll forward the same distance to the starting point. The software calculates the average, canceling rim and hub runout errors from every subsequent measurement. Skipping this step produces false readings.

Safety Before You Start

Setup and Measurement Procedure

1. Drive the vehicle onto the alignment rack. Perform a pre-alignment inspection: check tire pressure (inflate to placard spec), check for worn ball joints, tie-rod ends, wheel bearings, and bushings. Do not align a vehicle with worn steering or suspension components — adjustment will not hold.

2. Mount the alignment heads to all four wheels using the appropriate clamps. Tighten the locking knobs firmly. A loose head will move during the roll-back procedure and corrupt measurements.

3. Enter the vehicle year, make, model, and trim level into the alignment software. The system retrieves OEM specifications automatically.

4. Perform the run-out compensation (roll-back/roll-forward) procedure as directed by the software.

5. Observe live readings for all primary angles. Compare against the OEM spec windows displayed on screen. Green indicates in spec; yellow or red indicates out of spec.

6. Document pre-adjustment values on the printout.

Making Adjustments

Adjustment methods vary by vehicle design:

Final Steps

Torque all adjusted fasteners to OEM specification using a calibrated torque wrench. Re-check ride height. Print the final alignment report. The completed printout should show all primary angles in the green (within OEM spec). The instructor will verify both the printout and that no fasteners were left loose.

Key terms9

CamberThe inward or outward tilt of a tire from vertical when viewed from the front of the vehicle, expressed in degrees; affects tread wear and cornering.
ToeThe difference in the distance between the front edges and the rear edges of a pair of tires on the same axle; expressed in degrees or inches and is the primary cause of feathered tire wear.
CasterThe forward or rearward tilt of the steering axis when viewed from the side of the vehicle; positive caster improves directional stability and steering return-to-center.
Thrust angleThe angle between the vehicle's geometric centerline and the direction the rear axle is pointed; a non-zero thrust angle causes dog-tracking and front-tire wear.
Run-out compensationA calibration procedure performed by rolling the vehicle backward and forward a short distance so the alignment software can average out errors caused by rim and hub wobble.
Eccentric (cam) boltA fastener with an off-center head or collar that, when rotated within a slotted mount, shifts a suspension component to change camber or toe.
Thrust line alignmentAn alignment strategy in which the front wheels are steered to match the thrust line established by the rear axle, rather than the geometric centerline alone.
SetbackA condition in which one front wheel is positioned farther rearward than the other, often indicating prior collision damage to the frame or suspension mounting points.
Ride heightThe measured distance from a specified reference point on the vehicle body or frame to the ground; suspension geometry is engineered around a specific ride height, and alignment must be performed at that height.

Worked examples4

1. A vehicle's left front toe reading is +0.15° and the right front toe reading is +0.05°. The OEM total front toe specification is +0.20° ± 0.10°. Is total toe within specification, and what is the individual side split?
  1. Add the two individual toe readings to find total front toe: 0.15° + 0.05° = 0.20°.
  2. Compare total toe to the OEM specification: 0.20° is exactly at the center of the spec range (+0.10° to +0.30°), so total toe is within specification.
  3. Calculate the split: the difference between the two sides is 0.15° − 0.05° = 0.10°. A large split (one side significantly different from the other) can pull the steering wheel off-center even when total toe is correct. Check whether the OEM allows this split or requires individual side specs.
Answer: Total front toe is +0.20°, which is within the +0.20° ± 0.10° specification. The left side reads 0.10° more toe-in than the right side; if individual side specs are given, verify each side independently and adjust the tie-rod on the side that is furthest from its target first.
2. After loosening a cam bolt to adjust left rear camber, the technician moves the reading from −1.8° to −1.1°. The OEM specification is −0.8° ± 0.3° (acceptable range −0.5° to −1.1°). Is the angle now in spec?
  1. Identify the acceptable range: −0.5° to −1.1° negative camber.
  2. The current reading is −1.1°. Check whether −1.1° falls within the range −0.5° to −1.1°.
  3. −1.1° is equal to the most-negative limit of the specification, so it is at the edge of the green zone.
Answer: The angle is within specification (just at the negative limit). The technician should torque the cam bolt to OEM spec and recheck; if the angle shifts slightly during torquing and goes below −1.1°, a further small adjustment is needed before final torque.
3. A tie-rod sleeve adjustment changes front toe by approximately 0.06° per half-turn of the sleeve on this vehicle. The right front toe currently reads +0.28° and the OEM target is +0.10°. How many half-turns of the sleeve are needed, and in which direction does toe need to move?
  1. Calculate the correction needed: 0.28° − 0.10° = 0.18° of toe reduction (less toe-in is needed).
  2. Divide the correction by the change per half-turn: 0.18° ÷ 0.06° per half-turn = 3 half-turns.
  3. Reducing toe-in means the front of the tire must move outward. Shortening the tie-rod on most vehicles moves the wheel toward toe-out. Consult the OEM service information to confirm which direction to turn the sleeve for this vehicle's tie-rod orientation, then apply 3 half-turns and recheck live readings.
Answer: Approximately 3 half-turns of the tie-rod adjustment sleeve in the direction that reduces toe-in (typically shortening the outer tie-rod) should bring the right front toe from +0.28° to approximately +0.10°. Always recheck the live reading after adjustment rather than relying on the estimate alone.
4. The alignment printout shows front ride height at 13.5 inches on the left and 13.5 inches on the right. The OEM specification is 14.0 inches ± 0.5 inches. Is ride height acceptable for performing a valid alignment?
  1. Determine the acceptable ride-height range: 14.0 − 0.5 = 13.5 inches minimum; 14.0 + 0.5 = 14.5 inches maximum.
  2. Both sides measure 13.5 inches, which equals the minimum acceptable value.
  3. The measurement is at the lower limit but still within specification. Side-to-side difference is 0.0 inches, so there is no lean. Alignment may proceed, but the marginal ride height should be noted on the work order and the customer advised about spring condition.
Answer: Ride height of 13.5 inches is at the minimum allowable limit of the 13.5–14.5 inch range, so alignment can proceed. Document the finding and advise the customer that spring inspection is recommended, because ride height at the lower limit may indicate spring sag that could allow the vehicle to fall out of alignment prematurely.

The math in this lesson2

Learners divide toe correction by 0.06° per half-turn to find sleeve turns needed.
6.RP.37.NS.3
In class: Students mount alignment heads on all four wheels, level the system, and perform a run-out compensation (roll-back/roll-forward) procedure on an assigned vehicle; instructor checks head security and sensor calibration before the student proceeds. · Students navigate the alignment software, read live angle displays, compare readings to OEM specifications on screen, and document pre-alignment and post-alignment values on the alignment printout. · Students perform camber and toe adjustments using eccentric bolts, cam bolts, or shim kits as applicable to the vehicle, rechecking angles after each adjustment and performing a final ride-height check before printing the completed alignment report.
Materials: Four-wheel computerized alignment system (Hunter, Snap-on, or equivalent) with calibrated heads, alignment rack or drive-on lift, eccentric and cam bolt adjustment sets, alignment shim kit, torque wrench, ride-height measuring tape, OEM alignment specifications in shop software, alignment report printer
Check: Final alignment printout must show all primary angles within OEM specification (green on the printout); instructor reviews printout and vehicle for any loosened fasteners left un-torqued — both conditions must be met to pass.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

ASE A4 – Steering and Suspension
1. Which alignment angle describes the inward or outward tilt of a tire from vertical when viewed from the front of the vehicle?
ASE A4 – Steering and Suspension
2. A technician performs a four-wheel alignment but skips the run-out compensation procedure. What is the most likely consequence?
ASE A4 – Steering and Suspension
3. After adjusting left rear camber by loosening a cam bolt, what MUST the technician do before the vehicle is returned to the customer?
ASE A4 – Steering and Suspension
4. Thrust angle is the angle between the vehicle centerline and the direction the rear axle points. What driving symptom is most directly caused by a large positive thrust angle?
ASE A4 – Steering and Suspension
5. A vehicle's front total toe specification is +0.20° ± 0.15°. The alignment system displays the left front at +0.05° and the right front at +0.05°. Which statement best describes the situation?
ASE A4 – Steering and Suspension
6. Before recording alignment angles on a vehicle that has been sitting with a full load of cargo, the technician should FIRST:
ASE A4 – Steering and Suspension
7. Which tire wear pattern is most closely associated with excessive toe-out on a front-wheel-drive vehicle?
ASE A4 – Steering and Suspension
8. During a pre-alignment inspection, the technician finds the outer tie-rod end has noticeable play when the wheel is shaken laterally. What is the correct action?
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