Tire wear patterns, such as scuffing, cupping and outside shoulder wear, often are an indication of a larger problem with a vehicle's chassis components, reports Terry Hawkins, alignment specialist and senior instructor with Moog Automotive.

"The cause of uneven tire wear can be as simple as under inflation or over inflation," says Hawkins, "but it also can result from loose parts such as shocks, struts, ball joints, steering linkage or from weak springs." As a precaution against tire failure -- the No. 1 cause of highway breakdowns Hawkins recommends checking tires regularly for the following conditions:

Shoulder wear, which can be caused by under-inflation or hard cornering. Many shredded rubber tires seen along highways are the result of either under inflated tires, running too long and too hot, or from severe misalignment.

Center tread wear, which usually indicates over-inflation. Over inflation results when a vehicle owner tries to compensate for a slow leak by over inflating the tire to make it stay up longer.

Cupping can be caused by an unbalanced tire condition, faulty wheel bearings, loose parts, fatigued springs or weak shock absorbers. Check the condition of the shock by forcefully bouncing the front end of the car several times and releasing it on the down stroke. Failure of the vehicle to settle after two strokes suggests worn shocks or struts.

Camber or toe wear indicates misalignment due to loose, worn or bent steering linkage components. Many camber and toe wear problems can be traced to spring fatigue, which causes the vehicle's frame to ride closer to the road. Once the vehicle is below the manufacturer's height specifications, it is not possible to achieve the correct camber change designed into the suspension without replacing the springs. The vehicle also experiences excessive toe change as the suspension travels through jounce and rebound, again causing abnormal tire wear.

Diagonal scuffing and cupping across the face on rear tires signals problems with toe. Diagonal tread wear or cupping on rear tires is caused when the direction the vehicle's wheels are heading is not in line with the geometric center line of the vehicle. When this condition occurs, front-wheel steering can be affected and lead to tire slip or loss of traction or control. (Note: The wear pattern that develops on rear tires from improper toe will vary depending on tread design. Wear patterns from rear-wheel misalignment may resemble cupping on tires with highway tread design and diagonal scuffing on tires with an all season tread pattern.)

"Once a particular wear pattern develops," says Hawkins, "it will continue for the life of the tire." New tires will not correct a wear pattern problem and will soon begin to wear unevenly or prematurely if the cause of the problem is not repaired.

"In the classroom, I ask my students, 'When was the last time you replaced a set of tires that were worn evenly all the way down to the bottom of the tread?' You don't see that. Tires are commonly worn in patches or along their edges due to misalignment, or loose chassis parts."

In order to achieve optimum tire performance, vehicle owners should follow a preventive maintenance schedule that includes frequent checks of tire pressure and rotation of tires every 6,000 to 7,500 miles.

"Every car owner should have a tire gauge to monitor tire pressure once a month or whenever they check their oil," says Al Lynch, manager of technical services for Moog. "Tire pressure should conform with the manufacturer's recommendations, found inside the passenger door, door jamb, or glove box, to accommodate the rated vehicle load."

Tire wear patterns often are easier to feel than to see, adds Lynch. "Before feeling the tire," he cautions, "make sure there are no pieces of steel belting or metal embedded in the rubber which could result in a cut or splinter. Also make sure the vehicle is turned off and the parking brake is engaged.

"As you check each tire, be sure to feel both side to side and up and down the tread. If the tread pattern on the outside of the tires feels worn, either a camber or toe problem may exist which means it is time to have the wheel alignment checked by a qualified technician.