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 balljoint is to the rear of the lower balljoint (similar to the front wheels on a shopping cart).
Clues to caster problems include 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.
|Irregular tread wear signals alignment problems. A saw-tooth pattern (left) indicates a toe problem, and beveled wear (right) points to camber problems. (Courtesy Hunter Engineering)|
|Toe is the fore-and-aft difference in tire distance. Most vehicles are slightly toe-in for a lighter steering feel and to keep a slight pre-load on wheel bearings. (Courtesy Hunter Engineering)|
|To check the toe, park the vehicle on level ground with the tires straight ahead and the steering wheel centered. Jack up one of the front tires, secure the vehicle on jackstands, then spray-paint a stripe on the tread while spinning the tire.|
|Scribe a sharp concentric line in the paint on the tread by spinning the tire. We used a small nail held in a mini vise and lightly pressed against the tread to ensure a straight line.|