Alignment Fundamentals

Wheel alignment sets the angles of the wheels so that the vehicle tracks straight, the steering wheel sits centered and the tires wear evenly. A good alignment goes unnoticed. A bad one means a pull, a crooked wheel or a set of tires worn out early, and the customer feels it every day. The machine only measures. Your job is to make sure the car is ready and that the numbers mean what they seem to.

What You Will Be Able to Do

• Define camber, caster, toe and thrust angle and say what each does.
• Predict which way a vehicle pulls from side-to-side readings.
• Confirm a vehicle is ready for the rack.
• Make adjustments in the correct order and finish with a centered steering wheel.
• Separate a true alignment problem from a tire or brake problem.

The Three Main Angles

Specs for all these angles come from the vehicle maker. Numbers in this guide are only typical examples.

Camber

Camber is the tilt of the wheel in or out at the top, seen from the front of the vehicle.

• Negative camber: The top of the wheel leans in toward the vehicle. Too much wears the inner edge of the tire.
• Positive camber: The top of the wheel leans out. Too much wears the outer edge.
• Typical range: Many cars run slightly negative, often within about 1 degree of zero.
• Side-to-side difference: The vehicle tends to pull toward the side with more positive camber.

Caster

Caster is the tilt of the steering axis forward or back, seen from the side. Positive caster tilts the top of the axis toward the rear of the vehicle. Think of a shopping cart wheel, which trails behind its pivot and straightens itself.

• Job: Positive caster gives straight-line stability, and it makes the steering wheel return to center after a turn.
• Typical range: Modern cars often run about +3 to +7 degrees.
• Tire wear: Caster is not a direct tire wear angle.
• Side-to-side difference: The vehicle pulls toward the side with less positive caster.

Toe

Toe is the direction the wheels point compared with each other, seen from above.

• Toe-in: The front edges of the tires point toward each other.
• Toe-out: The front edges point away from each other.
• Tire wear: Toe wears tires faster than any other angle. Too much, either way, scrubs the tire sideways and feathers the tread into a saw-tooth edge, often with a road roar.
• Typical range: Total toe is usually a small figure close to zero, such as 0 to 0.20 degrees.

Worked Example: Reading a Pull

A vehicle pulls right and the printout shows these front readings.

Camber is nearly equal, so it is not the cause. Caster differs by 1.5 degrees. The vehicle pulls toward the side with less positive caster, and that is the right side, so the readings match the complaint. A small cross-caster difference is sometimes built in to offset road crown, so check the spec before you decide it is wrong.

Other Angles on the Printout

Thrust angle matters most. If the rear axle does not point straight ahead, the vehicle "dog-tracks", with the rear offset from the front, and the steering wheel sits crooked even when the front toe is right. A thrust alignment corrects for this by referencing the front toe to the rear axle's direction. Vehicles with adjustable rear toe can be brought close to zero first.

SAI and setback are usually not adjustable. A reading out of spec suggests a bent part or crash damage, and it needs a closer look.

When an Alignment Is Needed

• After replacing a tie rod, control arm, strut, ball joint or steering rack
• After lowering or lifting a vehicle
• After a hard curb or pothole strike
• With new tires, to protect the investment
• When tires show uneven wear
• When the vehicle pulls or the steering wheel is off center

Getting the Vehicle Ready

This is the most important part of the job. The machine cannot tell that a joint is loose or a tire is low. Work through these steps before you mount any targets, and record what you find.

1. Listen to the complaint. Road test the vehicle if the customer reports a pull, a wander or an off-center wheel.
2. Set tire pressures to the placard. A low tire tilts the vehicle and changes the readings.
3. Check the tires. Look for matched sizes and tread on each axle, and note the wear pattern on the repair order.
4. Inspect steering and suspension parts. Check tie rod ends, ball joints, control arm bushings, sway bar links and wheel bearings. A worn part lets the wheel move, so an alignment will not hold.
5. Measure ride height against the spec. Sagging springs change every angle, since geometry moves with height.
6. Remove heavy loads from the vehicle unless the maker says otherwise.

Warning: Do not align a vehicle with worn or loose steering parts. It may leave the shop looking correct on paper while still being unsafe. Quote the repair first, and align after it is done.

How the Rack Works

Most modern machines use cameras that read targets clamped to each wheel. Others use sensor heads fitted to each wheel.

1. Drive straight onto the rack and center the wheels on the turn plates. Check that the plates are locked until you need them.
2. Select the correct year, make, model and trim.
3. Mount the targets or heads to the wheels.
4. Perform compensation, usually by rolling the vehicle a short distance, so that the machine can account for any wheel runout.
5. Jounce the suspension to settle it, and set the brake pedal depressor if the machine calls for it.
6. Perform a caster sweep by turning the wheels left and right as the machine directs, then read the values.
7. Print or save the "before" readings.

Adjustment Order

Work from the rear of the vehicle to the front, and finish with front toe, because every other change moves it.

1. Rear camber, if adjustable.
2. Rear toe, if adjustable, which sets the thrust angle.
3. Front caster.
4. Front camber.
5. Center the steering wheel, and lock it with a holder.
6. Front toe, last, set evenly on each side.

Where the adjustment is depends on the vehicle:

Many cars have no factory camber or caster adjustment. Eccentric bolts or aftermarket kits can add adjustment on some of them. A solid rear axle usually has no adjustment, so a bad thrust angle may mean a bent housing or worn mounts.

Torque every fastener you moved to spec, including tie rod jam nuts and cam bolts. When you turn a tie rod, make sure the rack boot does not twist, since a twisted boot tears.

Finishing the Job

1. Recheck all readings after the last fastener is tight, since tightening can move an angle.
2. Road test the vehicle on a flat, straight road. Check for a centered wheel and no pull.
3. Print the report with both the before and after readings.
4. Give a copy to the customer and keep a copy in the shop file. It is your proof of work.

When It Is Not the Alignment

If the readings are good and the car still pulls, look elsewhere:

Common Mistakes

Check Your Understanding

1. A front tire is feathered across the tread, and the car tracks straight. Which angle do you suspect first? Toe. Feathering is the classic toe wear pattern.
2. Left camber is -1.2 degrees and right camber is -0.2 degrees. Which way will the vehicle tend to pull? Right, toward the side with more positive camber.
3. You find a loose outer tie rod end during the check, but the customer only wants an alignment. What do you do? Stop and report it. A worn tie rod is a safety issue, and the alignment will not hold until it is replaced.
4. The front toe is in spec, but the steering wheel sits crooked and the car seems to run sideways. Which reading do you check? Thrust angle, because the rear axle may not point down the centerline.
5. The readings are in spec and the car still pulls left. What is a quick next check? Swap the front tires side to side. If the pull moves to the right, a tire is the cause.

Key Takeaways

• Camber wears tire edges, toe feathers tires, and caster mainly affects stability and pull.
• A vehicle pulls toward more positive camber and less positive caster.
• Thrust angle shows where the rear axle points.
• Inspect, set pressures and check ride height before you touch the rack.
• Work rear to front, with front toe last.
• Keep the before and after readings for the customer and the shop.