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S
tudies 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 break-
downs 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 FirstâBasic 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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2
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 Vehicleâs 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
manufacturerâs information including:
⢠Recommended tire size
⢠Recommended tire inflation pressure
⢠Vehicle capacity weight (VCWâthe maximum occupant
and cargo weight a vehicle is designed to carry)
⢠Front and rear gross axle weight ratings (GAWRâ
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 ownerâs 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 pressureâ
measured in pounds per square inch (psi)âa tire
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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
vehicleâs design load limit, that is, the greatest
amount of weight a vehicle can safely carry and
the vehicleâs tire size.The proper tire pressure for
your vehicle is referred to as the ârecommended
cold inflation pressure.â (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 âmaximum permissible inflation pressureâ
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
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tire pressure
for the tires
on your
vehicle.
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Checking Tire Pressure
It is important to check your vehicleâs 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
vehicleâs tire information placard, certification label, or
in the ownerâs 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 âmissingâ
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 vehicleâs 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
manufacturerâs 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 tireâs
pressure when you can obtain a cold reading.
Tire Size
To maintain tire safety, purchase new tires that
are the same size as the vehicleâs original tires or
another size recommended by the manufacturer.
Look at the tire information placard, the ownerâs
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.
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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 âevenâ
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
Lincolnâs head upside down and facing you. If
you can see the top of Lincolnâs 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 vehicleâs
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 ownerâs 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
tireâs treadwear rate, traction performance, and
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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 tireâs performance
and longevity.
Treadwear grades are an indication of a tireâs
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 tireâs
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 âAAâ, âAâ, âBâ, and âCâ.
Temperature grades are an indication of a tireâs
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 tireâs resistance to heat is graded as
âAâ, âBâ, or âCâ.
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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 âPâ 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 tireâs 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 âRâ 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 tireâs load index.
It is a measurement of how much weight each tire can
support. You may find this information in your ownerâs
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 âM+Sâ or âM/Sâ 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 âDOTâ 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
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the tire was built. For example, the numbers 3197
means the 31st week of 1997. The other numbers are
marketing codes used at the manufacturerâs 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 tireâs 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 tireâs 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 âAAâ,âAâ, âBâ, and âCâ.
Temperature Letter
This letter indicates a tireâs 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 tireâs resistance to heat is graded
as âAâ, âBâ, or âCâ.
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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 âLTâ 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 tireâs 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 Safety Tips
Preventing Tire Damage
â˘
Slow down if you have to go over a pothole or
other object in the road.
â˘
Do not run over curbs or other foreign objects in
the roadway, and try not to strike the curb when
parking.
Tire Safety Checklist
â
Check tire pressure regularly (at least once a
month), including the spare.
â
Inspect tires for uneven wear patterns on the
tread, cracks, foreign objects, or other signs of
wear or trauma.
â
Remove bits of glass and other foreign objects
wedged in the tread
.
â
Make sure your tire valves have valve caps.
â
Check tire pressure before going on a long trip.
â
Do not overload your vehicle. Check the tire
information placard or ownerâs manual for the
maximum recommended load for the vehicle.
â
If you are towing a trailer, remember that some
of the weight of the loaded trailer is transferred
to the towing vehicle.
For more information, visit www.nhtsa.gov
or call 1-888-327-4236
DOT HS 809 361