To people who aren't familiar with automobile suspension science, the idea that a vehicle's wheels can go out of alignment might seem a little weird. After all, even a big-wheel tricycle can keep its wheels pointed straight ahead. Two-ton automobiles, on the other hand, have to deal with more stress than the average toddler's tricycle and require subtler engineering to cope with the conditions they encounter. That makes suspension alignment an ongoing part of any vehicle ownership experience.
Tire alignment is a complex topic that covers not only the wheels of a car, but also the vehicle's suspension system. This can be broken down into three main measurements: the toe, the camber, and the caster. The toe refers to the angle your tires point - inward or outward - when you look at your car from a bird's eye view. Slight changes to the wheel's toe angle so it points inward or outward can drastically affect the wear on and life of your wheels. The camber refers to the inward or outward lean of the tire in relation to the ground. Caster refers to the angle created from the steering axis when looking at the car from the side. Caster helps with the steering and stability of your car, so misalignment may lead to premature tire wear.
Why you might need an alignment
Because manufacturers typically build some adjustability into the suspension, it tends to go out of adjustment over time and use. Some vehicles are better at maintaining their adjustment settings than others, but even a vehicle that never goes out of adjustment still needs periodic alignments. Alignment settings change as components wear, as metal fatigues, and as tires wear down. Hard use such as driving on rough roads and off-roading can throw suspension out of alignment quickly. Your vehicle's wheels can go out of alignment almost immediately after it hits a big pothole or speed bump.
Manufacturers typically recommend checking suspension alignment at certain service intervals, most often either every second or third oil change or during tire rotations. Don't assume anything, though; every vehicle is different. Check your manufacturer service schedule for alignment inspection intervals.
Any change in a vehicle's driving characteristics, such as pulling to one side or vagueness in steering response can signal a need for realignment. These changes may go unnoticed for a long time because suspension tends to go out of alignment slowly. It might be a while before you realize something's up; and by then, your tires may have some oddball wear patterns. Tires that wear faster on one side than the other indicate suspension alignment issues. Changes to camber angle cause one edge of the tire to wear much faster than the other. In extreme cases, such as an improper suspension lowering kit, the inner edge of the tire can be completely bald while the outer edge looks brand new. Changes to toe angle tend to cause gradual feathering with uneven wear spreading at least halfway across the tread. Not all tire wear indicates bad alignment, though. Tires that are worn excessively on both edges indicate chronic under-inflation, while those worn heavily in one, big stripe down the middle are over-inflated.
Align or repair, or repair and align?
Most misalignment occurs over time and use, which is normal. In other cases, misalignment can be symptomatic of a suspension component that's bent, broken, missing or worn-out. The latter is common with stabilizer bar and steering end-links, which wear out over time and affect alignment. Inspect the suspension components and end-links for looseness, wear and ruptured grease boots before scheduling an alignment. Aligning a worn-out suspension won't fix anything. If you're unfamiliar with how to inspect or repair these things, then have a shop qualified to perform inspections do the alignment. It could save you some money over the long term - and regular inspections are good practice anyway.