The Basics of Car Wheel Alignment
Proper wheel alignment is an important part of the maintenance of your car. As a rule of thumb, alignment should be checked every time you purchase new tires or every 30,000 miles. Check your vehicle maintenance recommendations for an exact interval.
Alignment is a quick check and many tire and brake shops will do it for free if you're having other services done. Most vehicles rarely require adjustment. Proper adjustment is important because it affects tire wear, fuel efficiency, and can cause problems with other maintenance issues (power steering, bearings, etc).
There are three main angles that are checked for wheel alignments: camber, caster, and toe. Rear wheels may have a thrust angle check. Thanks to the McPherson Strut, however, most cars made in the past couple of decades likely require only a toe adjustment.
Because it's the most likely, we will start with this one. All four tires will have a toe-in or -out measurement. While some vehicles require a specific angle, most require that the toe be completely straight relative to the vehicle's frame.
A toe-in can be "pigeon toed" (angling inward) or "thrust" (angled outward). The toe is a measurement of the difference in distance between the front and rear of the tires on the same axle. So on the front, the steering tires will be measured front-to-front (closest to the bumper) and rear-to-rear (closest to the driver). The difference is the toe.
If the toe is "in" (or positive) then the front of the tires are closer to one another than the rear. If the opposite, the toe is "out" (or negative).
Camber is the angle of the wheel when viewed from the front. Many vehicles have a specific camber for "at rest," making them look funny when parked. When the vehicle is in motion, the camber flattens, putting the tire exactly perpendicular to the ground.
A negative camber is one where the top of the tire pushes inward towards the car while positive camber is pushing outward.
The caster angle is rarely adjusted, but could be an issue on older cars with a lot of steering linkage wear. It is the measurement of the wheel's turning point relative to the ground.
Imagine your car's wheel with a cross drawn through it so that the center (bullseye) of the cross is in the exact center of the wheel - the point where it connects to the car. The caster angle is the straight up-and-down line created by your cross. If this is off in any way, serious safety and maintenance concerns arise.
Adjustments to any of the alignments are made by technicians with specialized tools and equipment. The home mechanic is not likely to have the correct measurement tools to make a proper adjustment. "Eyeballing it" is not good enough - these are tiny fractions of inches that cannot be seen by the naked eye.
Most vehicles rarely require an alignment and many will never have a single adjustment required in their lifetimes.
How to diagnose an alignment problem