Your tires are the only part of the car that has direct contact with the road. Tires affect your vehicle handling, ride, braking, and safety. For optimum performance, tires must have the correct air pressure, tread depth, balance and the wheels of the vehicle must be properly aligned.

Checking your tires on a regular basis is an important step in protecting your safety and your automotive investment. Ideally, tire inspections should be performed monthly. If you drive over potholes and debris in the road, live in a cold climate, or drive long distances regularly, then you should inspect your tires more often.

Always inspect your tires before a long trip. The more often these inspections are performed, the easier it will be to find a small problem, such as a nail in your tire, and fix it before it becomes a more expensive and time-consuming issue.

Poor tire maintenance can lead to premature tire wear, a flat tire or even a blowout. Factors other than tires themselves also can affect tire wear. Worn suspension parts and wheel alignment both play a direct role in tire wear and performance.

Tire Problems to Look For During a Visual Inspection

• Over inflation: Too much air pressure causes mostly the tire's middle section to contact the road. This creates wear primarily in the center of the tread, with less wear at the tire's edges.
• Under inflation: Too little air pressure causes mostly the tire's outer edges to contact the road. This creates wear primarily on both edges of the tire tread, with less wear in the center.
• Tread wear on one edge of the tire: This typically occurs when the wheels are out of alignment.
• Erratic tread wear: This is often called cupping, and may mean the wheel is out of balance, or that the shock absorbers or other suspension components need to be replaced.
• Raised portion of the tread or sidewall: May indicate that one of the belts in the tire carcass has separated from those next to it.

Tire Problems to Look for While Driving

• Unusual vibration or thumping noise: Vibration or thumpingnoises can indicate an out-of-balance tire, one with tread that has a flat spot due to locking the wheels in a panic stop, or a tire with a separated belt.
• A pull to one side: While driving at a steady speed, pulling to one side may indicate an underinflated or damaged tire on the side of the car to which the vehicle pulls. If this is not the case, a brake problem or poor wheel alignment may be causing the pull.

Tire Tread Inspection

Tires depend on good tread condition depth to maintain traction and to shed water on wet roads. The tread should be checked at least once a month for excessive and uneven wear. The most accurate tread depth measurements are made with a simple tread depth gauge available at any parts store. Or you can use the traditional quarter and penny tests.

Insert a quarter into a tread groove with the top of Washington's head facing down. If the top of his head is not visible, your tires have at least 4/32" of tread and are fine for continued use. If you can see above the top of Washington's head, it is time to start shopping for new tires. Take measurements in three locations across the tire's tread: (1)outer edge, (2) center, and (3) inside edge.

The penny test is done in the same way, except that if you can see above the top of Lincoln's head your tires have less than 2/32" of tread, which is below the legal minimum and cause for immediate replacement. Tires worn to this level will also have visible wear indicators (thin bald strips) running from side to side across two or more tread segments.

The difference between 4/32" and 2/32" of tread depth might not seem like much, but based on research by the Tire Rack, America's largest independent tire tester the difference is significant. For example, a pickup truck traveling at 70 miles per hour that passes the penny test can take up to 499.5 feet to stop on wet pavement . However, the same truck has a stopping distance 122 feet shorter if it passes the quarter test instead. This is a 24 percent difference in stopping distance, and the equivalent of six or more car lengths.

The Tire Rack also reported that tires passing the quarter test exhibited better grip on the road under other driving conditions as well. Given these facts, AAA suggests you put that penny back in your piggy bank and instead use a quarter to check tire wear and determine when it is time for replacement.

Tire Inflation Inspection

Keeping your tires properly inflated is one of the easiest ways to help maintain good gas mileage and extend the life of your tires. Check your car's tire pressure at least once a month with a quality gauge, that measures pressure in pounds-per square inch (psi). Three types of tire pressure gauges are available at most auto parts stores: digital, dial and pen/stick types. The digital and dial designs tend to be more accurate and easier to read, although a good pen/stick gauge will do the job as well. Pressure gauges built into air hoses at gas stations are often abused and frequently inaccurate.

Recommended tire pressures are for cold tires. Therefore, tire pressure should be checked at ambient temperature before the vehicle has been driven. Checking tire pressure on a car that has warm tires can result in a pressure reading of up to 5 psi higher than the recommended pressure. The recommended inflation pressures for your car's tires can be found in the vehicle's owner's manual or on the tire information decal attached to the driver's door jamb. On older cars the decal may be in the glove box or inside the fuel filler door.

Checking Air Pressure

1. Remove the tire's valve cap.
2. Place the gauge over the tire's valve stem and press firmly so that no escaping air is heard. The tire gauge will indicate how much pressure is in the tire.
3. Adjust the tire's air pressure as needed. When adding air, push the air hose into the valve firmly, until the air stops escaping. Check the pressure every few seconds to help judge the amount of air going into the tire, until you reach the recommended air pressure. If the tire's pressure is greater than it should be, use the nipple on the tire gauge to press the center of the tire valve stem and release air.
4. Replace the valve cap.
5. Repeat the process for the other tires. Don't forget the spare tire.