An unbalanced wheel and tire assembly may create an annoying vibration when you drive on a smooth road and may result in irregular treadwear.

Misalignment of wheels in the front or rear, improperly operating brakes or shock absorbers, bent wheels, worn bushings and other mechanical problems cause uneven and rapid treadwear and should be corrected by a qualified mechanic. Front-wheel-drive vehicles, and those with independent rear suspension, require special attention with alignment of all four wheels.

These systems should be checked periodically as specified by the vehicle owner's manual or whenever you have an indication of trouble.

A bad jolt, such as hitting a pothole, can throw your front end out of alignment even if you had it checked an hour earlier. Such an impact can also bend the rim, causing a loss of air pressure, and damage your tires with little or no visible external indication.

Sometimes irregular tire wear can be corrected by rotating your tires. Consult your car owner's manual, the tire manufacturer or your tire dealer for the appropriate pattern for your vehicle.

If your tires show uneven wear, ask your tire dealer to check for and correct any misalignment, imbalance or other mechanical problem involved before rotation.

Sometimes front and rear tires on a vehicle use different pressures. After rotation, adjust individual tire air pressure to the figures recommended by the vehicle manufacturer for the new locations -- front or rear -- as shown on the tire placard in the vehicle.

The purpose of regularly rotating tires is to achieve more uniform wear for all tires on a vehicle. Before rotating your tires, always refer to your individual owner's manual for rotation recommendations. If no rotation period is specified, tires should be rotated approximately every 6,000 miles.

However, rotate your tires earlier if signs of irregular or uneven tire wear arise, and have the vehicle checked by a qualified technician to determine the cause of the wear problem. The first rotation is most important.

Do not include a "Temporary Use Only" spare tire in any of the rotation patterns shown. If you have a matching full-size tire as a spare and wish to include it in the rotation process, use one of the patterns shown. Insert the spare in the right rear position and place the tire that would have gone on the right rear in the trunk as the new spare.

Some tires cannot be rotated in the manners described. Such tires include uni-directional tires and tires with asymmetric tread designs. Also, some vehicles may have different-sized tires mounted on the front and rear axles, and these different-sized tires also have rotation restrictions. Check your owner's manual, or with your tire dealer or tire manufacturer, for the proper rotation recommendations for these special cases.