Car Maintenance Guide  
Tires

Link from:http://www.aaasouth.com/auto_maintenance_text.asp?section=Tires

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 vehicle must have the correct wheel alignment.

Checking your tires on a regular basis is an important step in protecting your safety as well as 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 problem.

However, properly trained and equipped service personnel should perform some tire maintenance, including puncture repairs, tire replacement (mounting on the rim), tire rotation and balancing, and wheel alignment.

Poor tire maintenance can lead to premature tire wear, tire blowout or a flat tire. Factors other than tires themselves also can affect tire wear. Worn suspension parts and the vehicle's 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 only the tire's middle section to touch the road. This creates wear primarily in the center of the tire, and not the tire's edges.		Under inflation: Too little air pressure causes the tire's sides to sag and the middle section pulls up from the road. This creates wear primarily on both edges of the tire, but not 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 ball joints need to be replaced.

Raised portion of the tread: may indicate that a radial belt inside the tire has separated.

Tire Problems to Look for While Driving

• Unusual vibration or thumping noise: Vibration or thumping noises can indicate a separated radial belt or badly chopped tire.
• A pull to one side: While driving at a steady speed, pulling to one side may indicate that tires on one side of the vehicle do not have equal air pressure with the tires on the other side of the vehicle. If this is not the case, then pulling to one side may be caused by a separated radial belt, or the need for a wheel alignment.

When driving conditions change, so should your tires. Most vehicles come equipped with all-season tires, which are designed to be used in all seasons and weather conditions. However, the tread pattern is not as aggressive as that of a dedicated snow tire. When driving in snow regions, it may be in your best interest to invest in tires specifically designed for greater traction in snow, sleet and icy conditions.

Snow Tires

Snow tires are the most common solution for driving in snow regions. They are designed to provide maximum traction in snow. The aggressive tread design provides traction when the condition of the road surface has unfavorable traction characteristics (snow, sleet, ice or mud).

Snow Chains

Snow chains are a set of chains that are attached to each other, and fit around the tire to improve traction on snow, sleet and ice. Show chains provide good traction, but they are hard on the roads. Before investing in snow chains, check to be sure they are legal where you plan to use them. Many states allow them to only be used during certain times of the year or when officials deem that the conditions warrant their use. Some states have laws against the use of snow chains.

Studded Snow Tires

Studded snow tires have the same basic design as regular snow tires, but incorporate a series of studs (small, metal spikes protruding from the tire's tread) for added traction on snow, sleet or ice covered surfaces. Similar to snow chains, the studs provide good traction but are hard on the roads. Check to be sure they are legal where you plan to use them. Many states allow studded snow tires to only be used during certain times of the year or when officials deem that the conditions warrant their use. Some states have laws against the use of studded snow tires.

Tips

• When purchasing snow tires, be sure they are labeled M/S (mud and snow). This will help ensure that you are in compliance with any local or state regulations that may require the use of snow tires. Most all-season tires are marked M/S.
• If snow chains are used, be sure they properly fit the tires and are in good condition.
• Check your tire pressure more often in cold weather. This will help avoid under inflation, which can hamper traction.
• Whether your vehicle has front or rear wheel drive, maximum traction and proper handling of the vehicle can only be achieved when snow tires are installed on all four wheels.
• If you decide to use only two snow tires, be sure to put them on the drive wheels of the vehicle. Drive wheels refer to the front wheels for front wheel drive vehicles and the rear wheels for rear wheel drive vehicles.

While you are checking the air pressure on each tire, visually inspect the tire's tread and sidewall for signs of wear and road debris that may have penetrated your tire.

Tires depend on good tread condition to maintain traction and to shed water on wet roads. Tread depth should be checked for excessive and uneven wear. Measure tire tread with a depth gauge (available at most parts stores) or a small ruler that has 1/16" graduations. Although it is not as accurate, you also can check tread depth by placing a penny in the tread of the tire. Insert the penny upside-down (inserting President Lincoln's head into the tire's tread). If President Lincoln's entire head is showing, it is time to replace your tires.

Take measurements in three locations across the tire's tread: (1) outer edge, (2) center, and (3) inside edge. The more tread the tire has remaining, the higher the reading will be. Uneven readings indicate improper tire inflation or the need for a wheel alignment. At 3/32 of an inch, it is time to shop for new tires. At 2/32 (1/16) of an inch, the tread wear has reached its legal limit in most states.

You also may see wear indicators (thin bald strips) revealed across two or more treads. This indicates that the tires have worn to an unsafe tread level, and should be replaced.

Tread?BR>wear?BR>indicators

Check your tire's pressure at least once a month with a tire gauge, which measures pressure in pounds-per-square inch (psi). Tire gauges are available at most auto parts stores. There are basically three types of air pressure gauges: pen, digital and dial. Dial gauges are easier to read then pen or stick designs.

Recommended tire pressures are for cold tires. Therefore, tire pressure should be checked when tires are cold. Checking tire pressure on a car that has hot tires can result in a pressure reading of up to 5 psi higher than the recommended pressure. Look for your tire's recommended air pressure in the vehicle's owner's manual, or inside the driver's side car door or glove compartment. Increase the pressure by 2 to 4 psi when carrying a heavy load or pulling a trailer.

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. It is in your best interest to purchase your own high-quality pressure gauge, because gas station and convenience store gauges are sometimes abused and may not be accurate.
3. Adjust the tire's air pressure if 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.

There are tire maintenance procedures that automotive repair professionals should do because they have the proper tools and knowledge. However, understanding these procedures will help you feel more confident in dealing with a repair provider.

Tire Rotation

Tires on the front and the rear of vehicles operate at different loads and perform different steering and braking functions, resulting in unequal wear patterns. To gain maximum life and performance from your tires, it is essential to rotate your vehicle's tires every 6,000 miles if you drive under normal driving conditions.

Wheel Balancing Properly balanced tires help minimize uneven wear and extend their life. When tires are balanced, small lead weights are attached to the wheels to limit vibration of the tire and wheels as they turn. Tires and wheels should be balanced when the tires are rotated (normally every 6,000 miles), after putting on new tires, after fixing a flat tire, and any other time a tire is removed from its rim.

Lead weights

Wheel Alignment

Wheel alignment is the measurement of the position of the wheels compared to specifications that the vehicle manufacturers recommend. Each vehicle has a specific wheel alignment range. If the wheel alignment isn't within its range, steering may become difficult and tires can wear unevenly. This can make them unsafe and also lower the vehicle's fuel mileage. You should check your wheel alignment every 12,000 miles or whenever you get your tires serviced. If the wheel alignment is out of specification, adjustments can be made by moving adjustable suspension parts.

A vehicle's wheels are properly aligned when you can drive down a road in a straight line without drifting or pulling to one side. Drifting and pulling to one side also can be caused by several other factors: a failed radial belt in a tire, low air pressure and worn or bent suspension parts can cause these conditions. A complete inspection should be made before a wheel alignment is performed.

Tires are stamped with traction, temperature and resistance-to-wear grade and ratings to help you purchase the right replacement tires for your vehicle and assist in choosing a tire that will meet your driving needs. All of your vehicle's tires should be the same size and grades (the exception being some performance cars that utilize front tires with a different size than the rear tires). These vehicles should still maintain the same size and grade for both front tires, and the same size and grade for both rear tires.

Treadwear, Traction and Temperature Grades: Treadwear indicates an estimate of how long the tire tread will last before the tire is worn out. Grading starts at 100 and goes up to 500, with 500 being the longest lasting tire wear grade. Tire wear also is determined by tire maintenance, your driving style and where you drive. The word "Traction" followed by a letter A, B or C (A providing the best traction) rates the tire's ability to stop on a wet road surface. Most quality tires will indicate an "A" grade. "Temperature" grades the tire's ability to withstand and dissipate heat. It also is graded A, B, or C, where "C" indicates a temperature grade that meets Federal requirements for passenger car tires, and A and B providing an even higher level of performance. This can be very critical if you live in a hot climate where road temperatures can increase tire temperature significantly.

DOT Number: This indicates compliance with the Department of Transportation safety standards. The "DOT" will be followed by the tire's identification number, which is used to identify a variety of characteristics about that tire (the manufacturer and plant code, tire size code, optional codes and the date the tire was tire is recalled. For example, 059 indicates a tire that was manufactured in the 5th week of 1999.

Size: This designates the size of the tire, such as a 15 inch or 16 inch tire. Below is a breakdown of a typical tire size and tire ratings that are located on the sidewall of the tire, and what the numbers and letters indicate.

To determine which tire size is recommended for your vehicle, check the tire sticker which can be found in one of the following locations: vehicle door edge, door post, glove box door, or fuel door.

Load Index/Load Rating: The load index is a number ranging from 0 to 279, and indicates the maximum load a tire can carry at the speed indicated by the speed rating.

Speed Index/Speed Rating: The speed rating is an alphabetical code (A through Z) that indicates the range of speeds at which the tire can carry a load corresponding to its load index. When replacing your tires, consult your vehicle owner's manual for the tire's recommended speed rating.