Understanding Tire Parts and Construction

Modern tire technology blends a unique mix of chemistry, physics, and engineering to give consumers a high degree of comfort, performance, efficiency, reliability, and safety. Many tires are custom-designed to meet the stresses and performance needs specified by the maker of a particular model vehicle. Every tire is carefully inspected, and random samples are pulled for additional safety tests. As part of these tests, tires are x-rayed, cut apart and examined, run on test wheels, or road-tested to evaluate handling, mileage, and traction performance. If properly cared for, tires can last a long time - usually from 40,000 to 80,000 miles, depending on the application.

The construction of a tire includes:

TREAD: Provides traction and cornering grip
BELTS: Stabilize and strengthen the tread
SIDEWALL: Protects the side of the tire from road and curb damage
"BODY PLY": Gives the tire strength and flexibility
BEAD: Assures an airtight fit with the wheel
INNERLINER: Keeps air inside the tire

How to Take Care of Your Tires

Proper tire care and safety are simple and easy. The Rubber Manufacturers Association (RMA) recommends taking five minutes every month and before every long trip to check your tires, including the spare. Just remember to "Be Tire Smart - Play Your PART: Pressure, Alignment, Rotation, Tread."

• Pressure - Under inflation results in unnecessary tire stress, irregular wear, loss of control and accidents. A tire can lose up to half of its inflation pressure and not appear to be flat!

• Alignment - A bad jolt from hitting a curb or pothole can throw your front end out of alignment and damage your tires. Have a tire dealer check the alignment periodically to ensure that your car is properly aligned.

• Rotation - Regularly rotating your vehicle's tires will help you achieve more uniform wear. Unless your vehicle's owners manual has a specific recommendation, the guideline for tire rotation is approximately every 5,000-8,000 miles.

• Tread - Advanced and unusual wear can reduce the ability of tread to grip the road in adverse conditions. Visually check your tires for uneven wear, looking for high and low areas or unusually smooth areas. Also, check for signs of damage.

How To Check Inflation Pressure

Look for this information in your vehicle. Refer to your vehicle's owners manual for the proper level of inflation; it may also be posted on the door post or in the glove box.

When you check the inflation pressure, make sure the tires are cool - meaning they are not hot from driving even a mile. (Note: If you have to drive a distance to get air, check and record the tire pressure first and add the appropriate inflation pressure when you get to the pump. It is normal for tires to heat up and the inflation pressure inside to increase as you drive. Never "bleed" or reduce air pressure when tires are hot.)

• Check inflation pressure once a month and before long trips.

• If you overfill the tire, you can release air by pushing on the metal stem in the center of the valve with a fingernail or the tip of a pen. Then recheck the pressure with your tire gauge.

• Replace the valve cap.

• Remember to check the spare. (Note: Some spare tires require higher inflation pressure).

Why Check Your Alignment?

If your car's suspension system is out of alignment, your tires will wear unevenly and you may experience handling problems. Potholes and rough roads can contribute to problems with alignment.

Front-wheel drive vehicles, and those with independent rear suspension require alignment of all four wheels.

Have a tire dealer check your alignment periodically as specified by your vehicle owner's manual or if handling problems develop, such as "pulling."

Also, have your tire balance checked periodically. An unbalanced tire and wheel assembly may result in irregular wear or vibration.

Why Rotate Your Tires?

Each tire on your car supports a different amount of weight; this unequal weight distribution causes your tires to wear at different rates. By rotating your tires, you can extend their useful life 

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. Refer to your vehicle's owners manual for rotation recommendations. If no rotation period is specified, tires should be rotated approximately every 5,000-8,000 miles.

Sometimes front and rear tires use different pressures. After rotation, adjust tire inflation pressure to the figures recommended by the vehicle manufacturer.

How to Check Tread

When the tread is worn down to 2/32 of an inch, tires must be replaced.  All tires have "wear bars," which are small, raised bars of rubber in the groove that indicate when tires are worn out. If your tread is worn down to the wear bars, it's time for a new tire.

A penny is a reliable tool to check tire tread.

1. Take a penny and put Lincoln's head into one of the grooves of the tire tread. If part of his head is covered by the tread, you're driving with the legal amount of tread.
2. If you can see all of Lincoln's head, it's time to replace the tire.

Visually check your tires for signs of uneven wear. You may have irregular tread wear if there are high and low areas or unusually smooth areas. Also, make sure no nails or other objects are embedded in the tire. Consult your tire dealer as soon as possible if you see problems.

To determine the percentage of wear once you have checked the remaining tread life of your tires, click here.

Other Important Information

Practice good driving habits, which will help keep your tires in good condition.

Tire Pressure Monitoring System (TPMS)
Vehicles equipped with Tire Pressure Monitoring Systems (TPMS) can help motorists detect loss of inflation pressure. Federal regulations require TPMS to warn drivers when tires are 25% under inflated. For many vehicles, this warning may be too late to prevent damage caused by under inflation. TPMS units are NOT a replacement for monthly tire pressure checks with a gauge.

• Obey posted speed limits.
• Always buckle your seat belt.
• Avoid fast starts, stops, and turns.
• Avoid potholes and other objects on the road.
• Do not run over curbs or hit your tires against the curb when parking.
• Do not overload your vehicle. Check your vehicle's tire information or owner's manual for the maximum recommended load for your vehicle.

How to Read a Tire Sidewall

35        Section Height (Aspect Ratio)
Z          Speed rating
R          Radial
20        Wheel Diameter (inches)
93W     Service Description