Most people think that wheel alignment is best left to the professionals. This is true in many respects, but some alignment specs are easy to check yourself, and toe is one aspect of alignment that can be checked at home. This can come in handy after replacing steering or suspension components so that the vehicle won't be wildly out of adjustment for the trip to the alignment shop, or at the very least provide a better understanding of the alignment process.
Factors affecting wheel alignment
In theory, all four wheels should be perpendicular to the ground and parallel to each other. When the vehicle starts pulling to one side – or after a sharp impact with a curb – most drivers suspect that the wheels might be out of alignment. Irregular tire wear, vibration and odd handling characteristics are other clues.
The three factors that affect alignment are toe-in, camber and caster. The first two can easily be checked at home.
Car front tires are slightly pigeon-toed to intentionally place a very slight load on the wheel bearings. Typical toe-in specs vary from one-thirty-second to one-eighth-inch, depending on the vehicle. Check a service manual for your car's acceptable range.
The best tip-off to a toe problem is a saw-tooth wear pattern that's equal on both front tires. If the tread blocks point toward the frame, then toe-in is excessive; pointing outward indicates too much toe-out.
Toe-in spec-check and adjustment are shown in the accompanying photos.
Two things to remember when measuring and adjusting toe: First, true spec is measured midway up the tires. If the car's body makes this impractical, take the front and rear measurements one-quarter of the way up the tires, then double that to get the true toe as it would be in the center of the tires. Also, an off-center steering wheel can sometimes be corrected by adjusting one tie-rod more than the other. (Steering wheel position has no effect on your final alignment.)
Camber is the measurement of tire lean in degrees. If the top of the tire tilts inward, the vehicle has negative camber; outward lean is positive camber. Most newer vehicles have slightly negative camber to improve stability and handling.
Two indicators of camber problems are the vehicle pulling to one side (the one with more positive camber or possibly less air in the tire) and uneven tire wear across the tread. Camber is easy to check with an angle finder and a straight edge, ideally one that's the same length as the wheel diameter so that tire sidewall bulge doesn't interfere with the straight edge.
Many front-wheel-drive cars don't have camber adjustments, and out-of-spec camber here often indicates bent or worn parts. On vehicles that have adjustable camber, the job can involve adding shims between the control arms and frame and turning cam bolts. Many people prefer to let an alignment shop make these adjustments, particularly if their car has independent rear suspension.
Caster is the angle of steering pivot in degrees. Just as water-skiers lean backward for stability, most vehicles are designed with slight negative caster – the upper ball joint is to the rear of the lower ball joint (similar to the front wheels on a shopping cart).
A clue to caster problems is the vehicle pulling to one side (the one with less positive caster). Heavy steering and wheel hopping over bumps are signs of too much positive caster, and light steering but excessive wander are clues of too much negative caster. Aligning to spec usually involves repairing or replacing chassis parts, so the average motorist is probably better off leaving caster corrections to the pros.
Taking a few minutes to check your alignment will make your tires last longer and your vehicle handle better. Even if you choose to have a shop align the vehicle, you'll have a better idea of the problem – and knowledge normally equals power.