Studies of tire safety show that 

maintaining proper tire pressure, 

observing tire and vehicle load limits 

(not carrying more weight in your vehicle than 

your tires or vehicle can safely handle), avoiding 

road hazards, and inspecting tires for cuts, 

slashes, and other irregularities are the most 

important things you can do to avoid tire failure, 

such as tread separation or blowout and flat 

tires. These actions, along with other care and 

maintenance activities, can also: 

• Improve vehicle handling 

•	 Help protect you and others from avoidable breakdowns and accidents 

• Improve fuel economy 

• Increase the life of your tires. 

This booklet presents a comprehensive overview 

of tire safety, including information on the 

following topics: 

• Basic tire maintenance 

• Uniform Tire Quality Grading System 

• Fundamental characteristics of tires 

• Tire safety tips. 

Use this information to make tire safety a regular 

part of your vehicle maintenance routine. 

Recognize that the time you spend is minimal 

compared with the inconvenience and safety 

consequences of a flat tire or other tire failure. 

Safety First–Basic Tire Maintenance 

Properly maintained tires improve the steering, 

stopping, traction, and load-carrying capability of 

your vehicle. Underinflated tires and overloaded 

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vehicles are a major cause of tire failure.

Therefore, as mentioned above, to avoid flat

tires and other types of tire failure, you should

maintain proper tire pressure, observe tire and

vehicle load limits, avoid road hazards, and

regularly inspect your tires. 

Finding Your Vehicle’s Recommended

Tire Pressure and Load Limits

Tire information placards and vehicle

certification labels contain information on tires

and load limits. These labels indicate the vehicle

manufacturer’s information including:

• Recommended tire size

• Recommended tire inflation pressure

• Vehicle capacity weight (VCW–the maximum occupant

and cargo weight a vehicle is designed to carry)

• Front and rear gross axle weight ratings (GAWR–

the maximum weight the axle systems are designed

to carry).

Both placards and certification labels are

permanently attached to the vehicle door edge,

door post, glove-box door, or inside of the trunk

lid. You can also find the recommended tire

pressure and load limit for your vehicle in the

vehicle owner’s manual. 

Understanding Tire Pressure 

and Load Limits

Tire inflation pressure is the level of air in the

tire that provides it with load-carrying capacity

and affects the overall performance of the

vehicle. The tire inflation pressure is a number

that indicates the amount of air pressure–

measured in pounds per square inch (psi)–a tire
requires to be properly inflated. (You will also 

find this number on the vehicle information 

placard expressed in kilopascals (kPa), which is 

the metric measure used internationally.) 

Manufacturers of passenger vehicles and light 

trucks determine this number based on the 

vehicle’s design load limit, that is, the greatest 

amount of weight a vehicle can safely carry and 

the vehicle’s tire size.The proper tire pressure for 

your vehicle is referred to as the “recommended 

cold inflation pressure.” (As you will read below, 

it is difficult to obtain the recommended tire 

pressure if your tires are not cold.) 

Because tires are designed to be used on more 

than one type of vehicle, tire manufacturers list 

the “maximum permissible inflation pressure” 

on the tire sidewall. This number is the greatest 

amount of air pressure that should ever be put 

in the tire under normal driving conditions. 

Remember, however, that the vehicle 

manufacturer, not the tire manufacturer, 

determines the correct 

3 

tire pressure 

for the tires 

on your 

vehicle. 
Checking Tire Pressure 

It is important to check your vehicle’s tire 

pressure at least once a month for the 

following reasons: 

• Most tires may naturally lose air over time. 

• Tires can lose air suddenly if you drive over a pothole 

or other object or if you strike the curb when parking. 

•	 With radial tires, it is usually not possible to determine 

underinflation by visual inspection. 

For convenience, purchase a tire pressure gauge 

to keep in your vehicle. Gauges can be 

purchased at tire dealerships, auto supply stores, 

and other retail outlets. 

The recommended tire inflation pressure that 

vehicle manufacturers provide reflects the 

proper psi when a tire is cold. The term cold 

does not relate to the outside temperature. 

Rather, a cold tire is one that has not been 

driven on for at least three hours. When you 

drive, your tires get warmer, causing the air 

pressure within them to increase. Therefore, to 

get an accurate tire pressure reading, you must 

measure tire pressure when the tires are cold or 

compensate for the extra pressure in warm tires. 

Steps for Maintaining Proper 

Tire Pressure 

Step 1: Locate the recommended tire pressure on the 

vehicle’s tire information placard, certification label, or 

in the owner’s manual. 

Step 2: Record the tire pressure of all tires. 

Step 3: If the tire pressure is too high in any of the 

tires, slowly release air by gently pressing on the tire 

valve stem with the edge of your tire gauge until you 

get to the correct pressure. 

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Step 4: If the tire pressure is 

too low, note the difference 

between the measured tire 

pressure and the correct tire 

pressure. These “missing” 

pounds of pressure are what you 

will need to add. 

Step 5: At a service station, add the 

missing pounds of air pressure to each tire that is 

underinflated. 

Step 6: Check all the tires to make sure they have the 

same air pressure (except in cases in which the front 

and rear tires are supposed to have different amounts 

of pressure). 

If you have been driving your vehicle and think 

that a tire is underinflated, fill it to the 

recommended cold inflation pressure indicated on 

your vehicle’s tire information placard or 

certification label. While your tire may still be 

slightly underinflated due to the extra pounds of 

pressure in the warm tire, it is safer to drive with 

air pressure that is slightly lower than the vehicle 

manufacturer’s recommended cold inflation 

pressure than to drive with a significantly 

underinflated tire. Since this is a temporary fix, 

don't forget to recheck and adjust the tire’s 

pressure when you can obtain a cold reading. 

Tire Size 

To maintain tire safety, purchase new tires that 

are the same size as the vehicle’s original tires or 

another size recommended by the manufacturer. 

Look at the tire information placard, the owner’s 

manual, or the sidewall of the tire you are 

replacing to find this information. If you have 

any doubt about the correct size to choose, 

consult with the tire dealer. 

5 
Tire Tread 

The tire tread provides the gripping action and 

traction that prevent your vehicle from slipping 

or sliding, especially when the road is wet or icy. 

In general, tires are not safe and should be 

replaced when the tread is worn down to 1/16 

of an inch. Tires have built-in treadwear 

indicators that let you know when it is time to 

replace your tires. These indicators are raised 

sections spaced intermittently in the bottom of 

the tread grooves. When they appear “even” 

with the outside of the tread, it is time to 

replace your tires. Another method for checking 

tread depth is to place a penny in the tread with 

Lincoln’s head upside down and facing you. If 

you can see the top of Lincoln’s head, you are 

ready for new tires. 

Tire Balance and Wheel Alignment 

To avoid vibration or shaking of the vehicle when 

a tire rotates, the tire must be properly balanced. 

This balance is achieved by positioning weights 

on the wheel to counterbalance heavy spots on 

the wheel-and-tire assembly. A wheel alignment 

adjusts the angles of the wheels so that they are 

positioned correctly relative to the vehicle’s 

frame. This adjustment maximizes the life of 

your tires and prevents your car from veering to 

the right or left when driving on a straight, level 

road. These adjustments require special 

equipment and should be performed by a 

qualified technician. 

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Tire Rotation

Rotating tires from front to back and from side

to side can reduce irregular wear (for vehicles

that have tires that are all the same size). Look in

your owner’s manual for information on how

frequently the tires on your vehicle should be

rotated and the best pattern for rotation.

Tire Repair

The proper repair of a punctured tire requires a

plug for the hole and a patch for the area inside

the tire that surrounds the puncture hole.

Punctures through the tread can be repaired if

they are not too large, but punctures to the

sidewall should not be repaired. Tires must be

removed from the rim to be properly inspected

before being plugged and patched.

Uniform Tire Quality Grading System

(UTQGS)

To help consumers compare a passenger car

tire’s treadwear rate, traction performance, and
temperature resistance, the federal government 

requires tire manufacturers to grade tires in 

these three areas. This grading system, known 

as the Uniform Tire Quality Grading System, 

provides guidelines for making relative 

comparisons when purchasing new tires. You 

also can use this information to inquire about 

the quality of tires placed on new vehicles. 

Although this rating system is very helpful when 

buying new tires, it is not a safety rating or 

guarantee of how well a tire will perform or 

how long it will last. Other factors such as 

personal driving style, type of car, quality of the 

roads, and tire maintenance habits have a 

significant influence on your tire’s performance 

and longevity. 

Treadwear grades are an indication of a tire’s 

relative wear rate. The higher the treadwear 

number is, the longer it should take for the tread 

to wear down. For example, a tire grade of 400 

should wear twice as long as a tire grade of 200. 

Traction grades are an indication of a tire’s 

ability to stop on wet pavement. A higher 

graded tire should allow you to stop your car on 

wet roads in a shorter distance than a tire with 

a lower grade. Traction is graded from highest 

to lowest as “AA”, “A”, “B”, and “C”. 

Temperature grades are an indication of a tire’s 

resistance to heat. Sustained high temperature 

(for example, driving long distances in hot 

weather), can cause a tire to deteriorate, leading 

to blowouts and tread separation. From highest 

to lowest, a tire’s resistance to heat is graded as 

“A”, “B”, or “C”. 

8 
Tire Fundamentals 

Federal law requires tire manufacturers to place 

standardized information on the sidewall of all 

tires. This information identifies and describes the 

fundamental characteristics of the tire and also 

provides a tire identification number for safety 

standard certification and in case of a recall. 

Information on Passenger Vehicle Tires 

Please refer to the diagram below. 

Radial 

Ratio of height to 

width (aspect ratio) 

Nominal width of 

tire in millimeters 

Passenger 

car tire 

pressure 

inflation 

permissible 

Max. 

Rim diameter 

code 

speed symbol 

Load index & 

U.S. DOT tire 

identification number 

Severe snow 

conditions 

Tire ply 

composition 

and materials 

used 

Treadwear, traction 

and temperature grades Max. load rating 

P 

The “P” indicates the tire is for passenger vehicles. 

Next number 

This three-digit number gives the width in 

millimeters of the tire from sidewall edge to 

sidewall edge. In general, the larger the number, the 

wider the tire. 

Next number 

This two-digit number, known as the aspect ratio, gives 

the tire’s ratio of height to width. Numbers of 70 or 

lower indicate a short sidewall for improved steering 

response and better overall handling on dry pavement. 

R 

The “R” stands for radial. Radial ply construction of 

tires has been the industry standard for the past 20 

years. 

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Next number 

This two-digit number is the wheel or rim diameter in 

inches. If you change your wheel size, you will have to 

purchase new tires to match the new wheel diameter. 

Next number 

This two- or three-digit number is the tire’s load index. 

It is a measurement of how much weight each tire can 

support. You may find this information in your owner’s 

manual. If not, contact a local tire dealer. Note: You 

may not find this information on all tires because it is 

not required by law. 

M+S 

The “M+S” or “M/S” indicates that the tire has some 

mud and snow capability. Most radial tires have these 

markings; hence, they have some mud and snow capa	

bility. 

Speed Rating 

The speed rating denotes the speed at which a tire is 

designed to be driven for extended periods of time. The 

ratings range from 99 miles per hour (mph) to 186 

mph. These ratings are listed below. Note: You may not 

find this information on all tires because it is not 

required by law. 

Q 99 mph H 130 mph 

R 106 mph V 149 mph 

S 112 mph W 168 mph* 

T 118 mph Y 186 mph* 

U 124 mph 

* For tires with a maximum speed capability over 149 mph, 

tire manufacturers sometimes use the letters ZR. For those 

with a maximum speed capability over 186 mph, tire manu	

facturers always use the letters ZR. 

U.S. DOT Tire Identification Number 

This begins with the letters “DOT” and indicates that the 

tire meets all federal standards. The next two numbers 

or letters are the plant code where it was manufactured, 

and the last four numbers represent the week and year 

10 
the tire was built. For example, the numbers 3197 

means the 31st week of 1997. The other numbers are 

marketing codes used at the manufacturer’s discretion. 

This information is used to contact consumers if a tire 

defect requires a recall. 

Tire Ply Composition and Materials Used 

The number of plies indicates the number of layers of 

rubber-coated fabric in the tire. In general, the greater 

the number of plies, the more weight a tire can support. 

Tire manufacturers also must indicate the materials in 

the tire, which include steel, nylon, polyester, and others. 

Maximum Load Rating 

This number indicates the maximum load in kilograms 

and pounds that can be carried by the tire. 

Maximum Permissible Inflation Pressure 

This number is the greatest amount of air pressure 

that should ever be put in the tire under normal 

driving conditions. 

UTQGS Information 

Treadwear Number 

This number indicates the tire’s wear rate. The higher 

the treadwear number is, the longer it should take for 

the tread to wear down. For example, a tire graded 

400 should last twice as long as a tire graded 200. 

Traction Letter 

This letter indicates a tire’s ability to stop on wet pave	

ment. A higher graded tire should allow you to stop 

your car on wet roads in a shorter distance than a tire 

with a lower grade. Traction is graded from highest to 

lowest as “AA”,”A”, “B”, and “C”. 

Temperature Letter 

This letter indicates a tire’s resistance to heat. The 

temperature grade is for a tire that is inflated properly 

and not overloaded. Excessive speed, underinflation or 

excessive loading, either separately or in combination, 

can cause heat build-up and possible tire failure. From 

highest to lowest, a tire’s resistance to heat is graded 

as “A”, “B”, or “C”. 

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Additional Information on Light Truck Tires 

Please refer to diagram below. 

Load 

range 

Light 

truck tire 

Maximum load 

& inflation when 

used as a single 

Load inflation 

limits 

Maximum load 

conditions 

Severe snow 

& inflation when 

used as a dual 

Tires for light trucks have other markings besides those 

found on the sidewalls of passenger tires. 

LT 

The “LT” indicates the tire is for light trucks. 

Max. Load Dual kg(lbs) 

at kPa(psi) Cold 

This information indicates the maximum load and tire 

pressure when the tire is used as a dual, that is, when 

four tires are put on each rear axle (a total of six or 

more tires on the vehicle). 

Max. Load Single kg(lbs) 

at kPa(psi) Cold 

This information indicates the maximum load and tire 

pressure when the tire is used as a single. 

Load Range 

This information identifies the tire’s load-carrying 

capabilities and its inflation limits. 

Snow Tires 

In some heavy snow areas, local governments 

may require true snow tires, those with very 

deeply cut tread. These tires should only be 

used in pairs or placed on all four wheels. Make 

sure you purchase snow tires that are the same 

size and construction type as the other tires on 

your vehicle. 

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Tire S

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