Everything 

Rides on It

2

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);	and

	 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	driver’s	side	vehicle	

door edge or door post. 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 amount 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.)
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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 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	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 difficult to 

determine some levels of underinflation by 

visual	inspection.

For	convenience,	buy	

a	tire	pressure	gauge	to	

keep	in	your	vehicle.	

Gauges can be purchased 

at	tire	dealerships,	auto	

supply	stores,	and	other	

retail	outlets.	
4

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 :	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.	

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	have	different	recommended	

inflation pressures).

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	
5

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, buy new tires that are the 

same	size	as	the	vehicle’s	original	tires	or	another	

size	recommended	by	the	vehicle	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.

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	2/32	of	an	inch.	
6

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.

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.

Be	aware	that	some	tires	may	have	a	onedirectional	tread	pattern	that	requires	them	to	be	
7

operated in one direction only. Therefore, these 

tires	should	only	be	rotated	from	front	to	back	on	

the	same	side	of	the	vehicle.

A Tire Rotation Example

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 

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	

buying	new	tires.	You	also	can	use	this	information	

to	inquire	about	the	quality	of	tires	placed	on	

new	vehicles.
8

Treadwear Grade

The treadwear grade is 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	graded	400	should	last	twice		

as	long	as	a	tire	graded	200.

Traction Performance Grade

The traction grade indicates 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 Resistance Grade

The temperature resistance grade 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.

Although this grading 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.

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. 

Examples	of	key	information	found	on	passenger	

vehicle	and	light	truck	tires	follow.	

Passenger Car Tires

RT AE WD RAE

ART 022 TC OI N A TEMPERATURE A

Radial

Ratio of height to

width (aspect ratio) 

Nominal width of

tire in millimeters 

Passenger

car tire 

Max.

permissible

inflation

pressure 

Treadwear, traction

and temperature grades 

Max. 

load rating

Tire ply

composition

and materials

used 

Severe snow

conditions 

U.S. DOT tire

identification number 

Rim diameter

code Load index &

speed rating 

Sidewall Outer Circle 

Passenger Car Tire 

The “P” indicates the tire is for passenger cars 

and	other	light	vehicles.

Nominal Width 

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.

Aspect Ratio

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.

Radial 

The “R” stands for radial. Radial ply 

construction	of	tires	has	been	the	industry	

standard	for	the	past	30	years.
0

Rim Diameter Code

This two-digit number is the wheel or rim 

diameter	in	inches.	If	you	change	your	wheel	

size,	you	will	have	to	buy	new	tires	to	match	the	

new	wheel	diameter.

Load Index 

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.

Speed Rating 

The speed rating denotes the maximum speed at 

which a tire is designed to be driven. The ratings 

range from 99 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	manufacturers	

must	use	the	letters	ZR.

Severe Snow Conditions 

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	capability.


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 buy snow tires that 

are the same size as the other tires 

on your vehicle.

Sidewall Inner Circle 

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	digits	

represent	the	week	and	year	the	tire	was	built.	

For	example,	the	digits	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.
Light-Truck Tires 

Tires for light trucks have other markings besides 

those	found	on	the	sidewalls	of	passenger	tires.

LT235/85R16 D 114/111Q

MAX. LOAD DUAL 1883 AB (2281 lbs) • AT 455 kPa (55 psi) CO DL L• AO

M• DEGNAR D

XA L. OAD S NI GLE 1110 xg (2623 lbs) • AT 455 kPa (55 psi) COLD •

Load

range 

Light

truck tire 

Maximum load

& inflation when

used as a single 

Maximum load

& inflation when

used as a dual 

Severe snow conditions

See page 9 

Light Truck Tire

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

Load Range

This information identifies the tire’s loadcarrying capabilities and its inflation limits.

Maximum Load Dual

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).*

Maximum Load Single

This information indicates the maximum load 

and	tire	pressure	when	the	tire	is	used	as	a	

single.*

*		Maximum	load	is	presented	in	kilograms	and	pounds	(kg/lbs).	

Maximum	tire	pressure	is	presented	in	kilopascals	and	pounds	

per	square	inch	(kPa/psi)	for	when	the	tire	is	cold.

2
Tire Safety Tips

Preventing Tire Damage

Slow	down	if	you	have	to	go	over	a	pothole	

or	other	object	in	the	road.

Do	not	run	over	curbs	or	foreign	objects	in	

the	roadway,	and	try	not	to	strike	the	curb	

when	parking.

Tire Safety Checklist

✔	 Check	tire	pressure	regularly	(at	least	once	a	

month),	including	the	spare.

✔	 Inspect	tires	for	cracks,	foreign	objects,	

uneven	wear	patterns	on	the	tread,	or	other	

signs	of	wear	or	trauma.

✔	 Remove	bits	of	glass	and	other	foreign	

objects	wedged	in	the	tread.

✔	 Make	sure	your	tire	valves	have	valve	caps.

✔	 Check	tire	pressure	before	going	on	a		

long	trip.

✔	 Do	not	overload	your	vehicle.	Check	the		

tire	information	placard	or	owner’s	manual	

for	the	maximum	recommended	load	for	

the	vehicle.

✔	 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 888-327-4236

DOT HS 810 900