Initial Inspection and Diagnostic Overview

Inspection and Verification
To maximize tire performance, inspect the tires for signs of incorrect inflation and uneven wear which may indicate a need for balancing, rotation or front suspension alignment. Tires should also be checked frequently for cuts, stone bruises, abrasions, blisters, and for objects that may have become embedded in the tread. More frequent inspections are recommended when rapid or extreme temperature changes occur or when road surfaces are rough or occasionally littered with foreign material.

As a further visible check of tire condition, tread wear indicators are molded into the bottom of the tread grooves. When these indicator bands become visible, new tires should be installed.

Tire Wear Diagnosis
New tires should be installed if the wear indicators are exposed or if there is severe shoulder wear. Shoulder wear is usually caused by either excessive camber or excessive toe on tires.

Sometimes incorrect rear toe settings or worn struts will cause severe "cupped" or "scalloped" tire wear on nondriven wheels.

Severely misadjusted rear toe will also cause other unusual wear patterns.

Tire Vibration Diagnosis
A tire vibration diagnostic procedure always begins with a road test. The road test and customer interview (if available) will provide much of the information needed to find the source of a vibration.

During the road test, drive the vehicle on a road that is smooth and free of undulations. If vibration is apparent, note and record the following:
- the speed at which the vibration occurs.
- what type of vibration occurs in each speed range.
+ mechanical or audible
- How the vibration is affected by changes in the following:
+ engine torque
+ vehicle speed
+ engine speed
- type of vibration - sensitivity: torque sensitive, vehicle speed sensitive or engine speed sensitive.

The following explanations help isolate the source of the vibration.

Torque Sensitive
This means that the condition can be improved or made worse by accelerating, decelerating, coasting, maintaining a steady vehicle speed or applying engine torque.

Vehicle Speed Sensitive
This means that the vibration always occurs at the same vehicle speed and is not affected by engine torque, engine speed or the transaxle gear selected.

Engine Speed Sensitive
This means that the vibration occurs at varying vehicle speeds when a different transaxle gear is selected. It can sometimes be isolated by increasing or decreasing engine speed with the transaxle in NEUTRAL or by stall testing with the transaxle in gear. If the condition is engine speed sensitive, the cause is probably not related to the tires.

If the road test indicates that there is tire whine, but no shake or vibration, the noise originates with the contact between the tire and the road surface.

A thumping noise usually means that the tire is flat or has soft spots making a noise as they slap the roadway. Tire whine can be distinguished from axle noise. Tire whine remains the same over a range of speeds.