Tire wear? Where?: a guide to diagnosing customers' problems.

In this article we'll examine a variety of chassis conditions that affect passenger-vehicle radial tire wear. As part of this, we'll look at distinct tire wear patterns and offer tips on tracing the cause in each case.

Alignment

Chassis misalignment is responsible for a host of tire wear problems.

Camber: On either front or rear axle positions, an off-camber problem will cause premature shoulder wear, as the incorrect vertical stance of the tire concentrates the scrub area away from the center of the tread.

Excess negative camber exists when the top of the tire leans too far inboard.

It results in an over-concentrated amount of scrub on the inside shoulder/tread area. When you see that, negative camber is the first thing to check out.

Conversely, excess positive camber will cause the top of the tire to lean outboard, as excess wear takes place on the outside tread/shoulder area.

A camber-only mis-adjustment will result in fairly smooth and even wear along the concentrated wear path. But if choppy, rough or scalloped wear is also evident, look for additional factors.

These can be worn shocks, loose control arm joints or bushings, loose strut to spindle bolts, etc.

Excess positive or negative camber coupled with low tire inflation will result in a more pronounced roughness along the wear path, especially at the edges of tread blocks along the concentrated scrub area.

Toe: Equal but incorrect toe settings cause both steer tires to roll ahead at an angle that's not parallel to the vehicle thrust line.

This will cause a "feathered" wear across the tread face. In turn this results in angled wear across the tread blocks that creates a slightly raised tread block edge in the direction of the excess toe.

In the case of toe-in, the raised featheredge will be toward the inboard edge of the tread blocks. With toe-out, the raised edges will be on the outboard side of the tread blocks.

In the case of unequal toe, it's automatically assumed that the tire with the greatest out-of-toe setting will wear irregularly.

For example, one wheel may be set at zero toe and the …