Transcript MEASURING SYSTEMS AND TOOLS

109
TIRES AND WHEELS
Automotive Technology, Fifth Edition
James Halderman
© 2011 Pearson Education, Inc.
All Rights Reserved
109 TIRES AND WHEELS
Figure 109-1 (a) A typical tire tread depth gauge. The center movable plunger is pushed down
into the groove of the tire.
Automotive Technology, Fifth Edition
James Halderman
© 2011 Pearson Education, Inc.
All Rights Reserved
109 TIRES AND WHEELS
Figure 109-1 (b) The tread depth is read at the top edge of the sleeve. In this example, the
tread depth is 6/32 in.
Automotive Technology, Fifth Edition
James Halderman
© 2011 Pearson Education, Inc.
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109 TIRES AND WHEELS
Figure 109-2 Wear indicators (wear bars) are strips of bald tread that show when the tread
depth is down to 2/32 in., the legal limit in many states.
Automotive Technology, Fifth Edition
James Halderman
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109 TIRES AND WHEELS
Figure 109-3 The tire tread runs around the circumference of the tire, and its pattern helps
maintain traction. The ribs provide grip, while the grooves direct any water on the road away from
the surface. The sipes help the tire grip the road.
Automotive Technology, Fifth Edition
James Halderman
© 2011 Pearson Education, Inc.
All Rights Reserved
109 TIRES AND WHEELS
Figure 109-4 Hydroplaning can occur at speeds as low as 30 mph (48 km/h). If the water is
deep enough and the tire tread cannot evacuate water through its grooves fast enough, the tire can
be lifted off the road surface by a layer of water. Hydroplaning occurs at lower speeds as the tire
becomes worn.
Automotive Technology, Fifth Edition
James Halderman
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109 TIRES AND WHEELS
Figure 109-5 Typical construction of a radial tire. Some tires have only one body ply, and some
tires use more than two belt plies.
Automotive Technology, Fifth Edition
James Halderman
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109 TIRES AND WHEELS
Figure 109-6 The major splice of a tire can often be seen and felt on the inside of the tire. The
person who assembles (builds) the tire usually places a sticker near the major splice as a means of
identification for quality control.
Automotive Technology, Fifth Edition
James Halderman
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109 TIRES AND WHEELS
Figure 109-7 Tire construction is performed by assembling the many parts of a tire together on a
tire-building machine.
Automotive Technology, Fifth Edition
James Halderman
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109 TIRES AND WHEELS
Figure 109-8 After the entire tire has been assembled into a completed “green” tire, it is placed
into a tire-molding machine where the tire is molded into shape and the rubber is changed
chemically by the heat. This nonreversible chemical reaction is called vulcanization.
Automotive Technology, Fifth Edition
James Halderman
© 2011 Pearson Education, Inc.
All Rights Reserved
109 TIRES AND WHEELS
FREQUENTLY ASKED QUESTION: Why Do I
Get Shocked by Static Electricity When I
Drive a Certain Vehicle? Static electricity
builds up in insulators due to friction of the
tires with the road. Newer tires use silica and
contain less carbon black in the rubber, which
makes the tires electrically conductive.
Because the tires cannot conduct the static
electricity to the ground, static electricity
builds up inside the vehicle and is discharged
through the body of the driver and/ or
passenger whenever the metal door handle is
touched.
NOTE: Toll booth operators report being
shocked by many drivers as money is being
passed between the driver and the toll booth
operator.
Newer tire sidewall designs that use silica
usually incorporate carbon sections that are
used to discharge the static electricity to
ground. To help reduce the static charge
buildup, spray the upholstery with an
antistatic spray available at discount and
grocery stores.
Automotive Technology, Fifth Edition
James Halderman
© 2011 Pearson Education, Inc.
All Rights Reserved
109 TIRES AND WHEELS
FREQUENTLY ASKED QUESTION: How
Much Does Tire Pressure Change with a
Change in Temperature? As the
temperature of a tire increases, the pressure
inside the tire also increases. The general
amount of pressure gain (when temperatures
increase) or loss (when temperatures
decrease) is as follows:
10°F increase causes 1 PSI increase
10°F decrease causes 1 PSI decrease
For example, if a tire is correctly inflated to 35
PSI when cold and then driven on a highway,
the tire pressure may increase 5 PSI or more.
CAUTION: DO NOT LET AIR OUT OF A HOT
TIRE! If air is released from a hot tire to bring
the pressure down to specifications, the tire
will be underinflated when the tire has cooled.
The tire pressure specification is for a cold tire.
Always check the tire pressures on a vehicle
that has been driven fewer than 2 miles (3.2
km).
Air pressure in the tires also affects fuel
economy. If all four tires are underinflated
(low on air pressure), fuel economy is reduced
about 0.1 mile per gallon (mpg) for each 1 PSI
low. For example, if all four tires were inflated
to 25 PSI instead of 35 PSI, not only is tire life
affected but fuel economy is reduced by about
1 mile per gallon
(10 X 0.1 = 1 mpg).
Automotive Technology, Fifth Edition
James Halderman
© 2011 Pearson Education, Inc.
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109 TIRES AND WHEELS
Figure 109-9 Notice that the overall outside diameter of the tire remains almost the same and at
the same time the aspect ratio is decreased and the rim diameter is increased.
Automotive Technology, Fifth Edition
James Halderman
© 2011 Pearson Education, Inc.
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109 TIRES AND WHEELS
FREQUENTLY ASKED QUESTION: How Much Bigger Can I Go? Many owners think they can improve their vehicle by
upgrading the tire size over the size that comes from the factory to make their vehicle look sportier and ride and handle
better. When changing tire size, there are many factors to consider:
1. The tire should be the same outside diameter as the original to maintain the proper suspension, steering, and ride height
specifications.
2. Tire size affects vehicle speed sensor values, ABS brake wheel sensor values that can change automatic transmission
operation, and ABS operation.
3. The tire should not be so wide as to contact the inner wheel well or suspension components.
4. Generally, a tire that is 10 mm wider is acceptable. For example, an original equipment tire size 205/75 X 15 (outside
diameter = 27.1 in.) can be changed to 215/75 X 15 (outside diameter = 27.6 in.). This much change is less than 1/2 in. in
width and increases the outside diameter by 1/2 in.
NOTE: Outside diameter is calculated by adding the wheel diameter to the cross-sectional height of the tire, multiplied by 2.
- SEE FIGURE 109–9 .
5. Whenever changing tires, make sure that the load capacity is the same or greater than that of the original tires. 6. If
wider tires are desired, a lower aspect ratio is required to maintain the same, or close to the same, overall outside diameter
of the tire.
Old
New
P205/75 × 15
P215/70 × 15
205 × 0.75= 154 mm
215 × 0.70 = 151 mm
Notice that the overall sidewall height is generally maintained.
If even larger tires are needed, then 225/60 15s may be OK–let’s check the math:
225 X 0.60 = 135 mm
Notice that this is much too short a sidewall height when compared with the original tire (see no. 6).
7. Use the “plus 1” or “plus 2” concept. When specifying wider tires, the sidewall height must be reduced to maintain the
same, or close to the same, original equipment specifications. The “plus 1” concept involves replacing the wheels with
wheels 1 in. larger in diameter to compensate for the lower aspect of wider tires.
Original
Plus 1
205/75 X 15
225/60 X 16
The overall difference in outside diameter is only 0.5 in., even though the tire width has increased from 205 mm to 225 mm
and the wheel diameter has increased by 1 in. If money is no object and all-out performance is the goal, a “plus 2” concept
can also be used (use a P245/50 X 17 tire and change to 17-in.-diameter wheels).
Here the overall diameter is within 1/20” of the original tire/wheel combination, yet the tire width is 1.6 inches (40 mm)
wider than the original tire. Refer to the section entitled “Wheels” later in this chapter for proper wheel back spacing and
offset when purchasing replacement wheels.
Automotive Technology, Fifth Edition
James Halderman
© 2011 Pearson Education, Inc.
All Rights Reserved
109 TIRES AND WHEELS
FREQUENTLY ASKED QUESTION: What Effect Does
Tire Size Have on Overall Gear Ratio? Customers often
ask what effect changing tire size has on fuel economy
and speedometer readings. If larger (or smaller) tires are
installed on a vehicle, many other factors also will change.
These include the following:
1. Speedometer reading. If larger-diameter tires are used,
the speedometer will read slower than you are actually
traveling. This can result in speeding tickets!
2. Odometer reading. Even though larger tires are said to
give better fuel economy, just the opposite can be
calculated! Since a larger-diameter tire travels farther
than a smaller-diameter tire, the larger tire will cause the
odometer to read a shorter distance than the vehicle
actually travels. For example, if the odometer reads 100
miles traveled on tires that are 10% oversized in
circumference, the actual distance traveled is 110 miles.
3. Fuel economy. If fuel economy is calculated on miles
traveled, the result will be lower fuel economy than for the
same vehicle with the original tires.
Calculation: mph = RPM × diameter × 3.14
gear ratio
RPM = mph × gear × ratio
diameter × 3.14
gear ratio = RPM × diameter × 3.14
mph
Automotive Technology, Fifth Edition
James Halderman
© 2011 Pearson Education, Inc.
All Rights Reserved
109 TIRES AND WHEELS
Figure 109-10
Cross-sectional view of a typical tire showing the terminology.
Automotive Technology, Fifth Edition
James Halderman
© 2011 Pearson Education, Inc.
All Rights Reserved
109 TIRES AND WHEELS
FREQUENTLY ASKED QUESTION: If I Have an Older Vehicle, What Size Tires Should I
Use? Newer radial tires can be used on older-model vehicles if the size of the tires is selected
that best matches the original tires. See the following cross-reference chart.
Cross-Reference Chart
(This Chart Does Not Imply Complete Interchangeability.)
Pre-1964 1965 to 1972
Metric 70 Series
80 Series Metric
Alpha Numeric
P-Metric 75 Series
78 Series
PRadial
Radial
590-13
P175/70R13
640-13
P185/70R13
725-13
P205/70R13
590-14
P185/70R14
650-14
P195/70R14
700-14
P205/70R14
750-14
P215/70R14
800-14
P225/70R14
850-14
P235/70R14
590-15
P175/70R15
650-15
P185/70R15
640-15
P205/70R15
670-15
P215/70R15
710-15
P225/70R15
760-15
P235/70R15
800-15
P235/70R15
820-15
P255/70R15
600-13
165-13
A78-13
P165/75R13
650-13
175-13
B78-13
P175/75R13
700-13
185-13
D78-13
P185/75R13
645-14
155-14
B78-14
P175/75R14
695-14
175-14
C78-14
P185/75R14
735-14
185-14
E78-14
P195/75R14
775-14
195-14
F78-14
P205/75R14
825-14
205-14
G78-14
P215/75R14
855-14
215-14
H78-14
600-15
165-15
A78-15
P165/75R15
685-15
175-15
C78-15
P175/75R15
735-15
185-15
E78-15
P225/75R14
P195/75R15
775-15
195-15
F78-15
P205/75R15
815-15
205-15
G78-15
P215/75R15
855-15
215-15
H78-15
P225/75R15
885-15
230-15
J78-15
P225/75R15
900-15
235-15
L78-15
P235/75R15
Automotive Technology, Fifth Edition
James Halderman
© 2011 Pearson Education, Inc.
All Rights Reserved
109 TIRES AND WHEELS
FREQUENTLY ASKED QUESTION: What Does the Little “e” Mean on the
Sidewall? Most countries have government agencies that regulate standards for
motor vehicles sold and/or driven within their jurisdiction. In the United States, the
U.S. Department of Transportation and National Highway Traffic Safety Administration
are responsible for developing many of the nationwide standards for vehicles. Tires
that are certified by their manufacturers to meet U.S. standards are branded with
“DOT” (Department of Transportation) preceding the Tire Identification Code on their
sidewall. In Europe, because so much personal and commercial travel extends beyond
the borders of any one country, the Economic Commission for Europe (E.C.E.) helps
develop uniform motor vehicle standards for its member countries to regulate and
standardize passenger and commercial vehicle components.
Besides physical specifications, the E.C.E. standards now require tire “pass-by” noise to meet
specific limits. These standards were phased-in starting in 2004. The tires must pass noise
emission testing, and the standards will continue to expand in scope until 2009, when the
standards will be applied to all tires sold in Europe.
The E.C.E. symbol on a tire’s sidewall identifies that the manufacturer certifies that the tire meets
all regulations, including the load index and speed symbol that appear in its service description.
The letter “e” and number code combination (positioned in a circle or rectangle) identify the
country originally granting approval, followed by two digits indicating the Regulation Series under
which the tire was approved. Tires that have also been tested and meet the “pass-by” noise limits
can have a second E.C.E. branding followed by an “-s” (for sound ). = SEE FIGURE 109–12 .
The following list indicates selected E.C.E. codes and the countries they represent:
Code
E1
E2
E3
E4
E5
E6
E7
E8
E9
E10
E11
E12
E13
Country
Germany
France
Italy
Netherlands
Sweden
Belgium
Hungary
Czech Republic
Spain
Yugoslavia
United Kingdom
Austria
Luxembourg
Code
E14
E15
E16
E17
E18
E19
E20
E21
E22
E23
E24
E25
E26
Automotive Technology, Fifth Edition
James Halderman
Country
Switzerland
Norway
Finland
Denmark
Romania
Poland
Portugal
Russian Federation
Greece
Ireland
Croatia
Slovenia
Slovakia
© 2011 Pearson Education, Inc.
All Rights Reserved
109 TIRES AND WHEELS
FREQUENTLY ASKED QUESTION: What Does the Little “e” Mean on the Sidewall? Most countries have
government agencies that regulate standards for motor vehicles sold and/or driven within their jurisdiction. In the
United States, the U.S. Department of Transportation and National Highway Traffic Safety Administration are
responsible for developing many of the nationwide standards for vehicles. Tires that are certified by their
manufacturers to meet U.S. standards are branded with “DOT” (Department of Transportation) preceding the Tire
Identification Code on their sidewall. In Europe, because so much personal and commercial travel extends beyond
the borders of any one country, the Economic Commission for Europe (E.C.E.) helps develop uniform motor
vehicle standards for its member countries to regulate and standardize passenger and commercial vehicle
components.
Besides physical specifications, the E.C.E. standards now require tire “pass-by” noise to meet specific limits. These standards
were phased-in starting in 2004. The tires must pass noise emission testing, and the standards will continue to expand in scope
until 2009, when the standards will be applied to all tires sold in Europe.
The E.C.E. symbol on a tire’s sidewall identifies that the manufacturer certifies that the tire meets all regulations, including the load
index and speed symbol that appear in its service description.
The letter “e” and number code combination (positioned in a circle or rectangle) identify the country originally granting approval,
followed by two digits indicating the Regulation Series under which the tire was approved. Tires that have also been tested and
meet the “pass-by” noise limits can have a second E.C.E. branding followed by an “-s” (for sound ). = SEE FIGURE 109–12 .
The following list indicates selected E.C.E. codes and the countries they represent:
Code
E1
E2
E3
E4
E5
E6
E7
E8
E9
E10
E11
E12
E13
Country
Germany
France
Italy
Netherlands
Sweden
Belgium
Hungary
Czech Republic
Spain
Yugoslavia
United Kingdom
Austria
Luxembourg
Code
E14
E15
E16
E17
E18
E19
E20
E21
E22
E23
E24
E25
E26
Country
Switzerland
Norway
Finland
Denmark
Romania
Poland
Portugal
Russian Federation
Greece
Ireland
Croatia
Slovenia
Slovakia
Automotive Technology, Fifth Edition
James Halderman
© 2011 Pearson Education, Inc.
All Rights Reserved
109 TIRES AND WHEELS
FREQUENTLY ASKED QUESTION: What Does the Little “e” Mean on the Sidewall?
Most countries have government agencies that regulate standards for motor vehicles sold
and/or driven within their jurisdiction. In the United States, the U.S. Department of
Transportation and National Highway Traffic Safety Administration are responsible for
developing many of the nationwide standards for vehicles. Tires that are certified by their
manufacturers to meet U.S. standards are branded with “DOT” (Department of
Transportation) preceding the Tire Identification Code on their sidewall. In Europe,
because so much personal and commercial travel extends beyond the borders of any one
country, the Economic Commission for Europe (E.C.E.) helps develop uniform motor
vehicle standards for its member countries to regulate and standardize passenger and
commercial vehicle components.
Besides physical specifications, the E.C.E. standards now require tire “pass-by” noise to meet specific
limits. These standards were phased-in starting in 2004. The tires must pass noise emission testing,
and the standards will continue to expand in scope until 2009, when the standards will be applied to
all tires sold in Europe.
The E.C.E. symbol on a tire’s sidewall identifies that the manufacturer certifies that the tire meets all
regulations, including the load index and speed symbol that appear in its service description.
The letter “e” and number code combination (positioned in a circle or rectangle) identify the country
originally granting approval, followed by two digits indicating the Regulation Series under which the
tire was approved. Tires that have also been tested and meet the “pass-by” noise limits can have a
second E.C.E. branding followed by an “-s” (for sound ). = SEE FIGURE 109–12 .
The following list indicates selected E.C.E. codes and the countries they represent:
Code
E1
E2
E3
E4
E5
E6
E7
E8
E9
E10
E11
E12
E13
Country
Germany
France
Italy
Netherlands
Sweden
Belgium
Hungary
Czech Republic
Spain
Yugoslavia
United Kingdom
Austria
Luxembourg
Code
E14
E15
E16
E17
E18
E19
E20
E21
E22
E23
E24
E25
E26
Country
Switzerland
Norway
Finland
Denmark
Romania
Poland
Portugal
Russian Federation
Greece
Ireland
Croatia
Slovenia
Slovakia
Automotive Technology, Fifth Edition
James Halderman
© 2011 Pearson Education, Inc.
All Rights Reserved
109 TIRES AND WHEELS
CHART 109–1 Speed ratings are based on continuous operation at the speed rating speed.
*The exact speed rating for a particular Z-rated tire is determined by the tire manufacturer and may
vary according to size. For example, not all Brand X Z-rated tires are rated at 170 mph, even though
one size may be capable of these speeds.
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James Halderman
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109 TIRES AND WHEELS
Figure 109-11
Typical sidewall markings for load index and speed rating following the tire size.
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James Halderman
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109 TIRES AND WHEELS
Figure 109-12 The E.C.E. symbol on a sidewall of a tire. Notice the small -s at the end,
indicating that the tire meets the “pass-by” noise limits.
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109 TIRES AND WHEELS
Figure 109-13 A typical door placard used on a General Motors vehicle indicating the
recommended tire inflation. Note that the information also includes the tire size and speed rating of
the tire as well as the recommended wheel size.
Automotive Technology, Fifth Edition
James Halderman
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109 TIRES AND WHEELS
Figure 109-14 Conicity is a fault in the tire that can cause the vehicle to pull to one side due to
the cone effect (shape) of the tire.
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James Halderman
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109 TIRES AND WHEELS
Figure 109-15 Notice the angle of the belt material in this worn tire. The angle of the belt fabric
can cause a “ply steer” or slight pulling force toward one side of the vehicle.
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James Halderman
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109 TIRES AND WHEELS
FREQUENTLY ASKED QUESTION: Is There
a Rule-of-Thumb for Rim Size? According
to the Tire and Rim Association, Inc., the
answer is no. Each tire size has a designated
rim width on which it is designed to be
mounted so as to provide the best
performance and wear. The width of the
specified rim also varies with rim diameter. A
235/45 X 17 tire may require a 7.5-in. rim but
a 235/45 X 19 tire may require an 8.0-in. rim.
A rule-of-thumb that has been used is to
multiply the width of the rim by 33.55 to
determine the approximate tire size for the
rim. For example, consider the following.
Rim width
tire
Rim width
tire
Rim width
tire
Rim width
tire
Rim width
tire
Rim width
tire
Rim width
tire
Rim width
tire
Rim width
tire
Rim width
mm) tire
5.0 in. X 33.55 = 167.85 (165 mm)
5.5 in. X 33.55 = 184.50 (185 mm)
6.0 in. X 33.55 = 201.30 (195 mm)
6.5 in. X 33.55 = 218.00 (215 mm)
7.0 in. X 33.55 = 234.90 (235 mm)
7.5 in. X 33.55 = 252.00 (245 mm)
8.0 in. X 33.55 = 268.00 (265 mm)
8.5 in. x 33.55 = 285.00 (285 mm)
9.0 in. X 33.55 = 302.00 (305 mm)
10.0 in. X 33.55 = 335.60 (335
Always check with the tire manufacturer as to
the specified tire rim width that should be
used.
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James Halderman
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109 TIRES AND WHEELS
Figure 109-16 Slip angle is the angle between the direction the tire tread is heading and the
direction it is pointed.
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109 TIRES AND WHEELS
Figure 109-17
tire sidewall.
Typical “Uniform Tire Quality Grading System” (UTQGS) ratings imprinted on the
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109 TIRES AND WHEELS
REAL WORLD FIX: Tire Date Code
Information Saved Me Money! This author
was looking at a three-year-old vehicle when I
noticed that the right rear tire had a build date
code newer than the vehicle. I asked the
owner, “How badly was this vehicle hit?” The
owner stumbled and stuttered a little, then
said, “How did you know that an accident
occurred?” I told the owner that the right rear
tire, while the exact same tire as the others,
had a date code indicating that it was only one
year old, whereas the original tires were the
same age as the vehicle. The last three
numbers of the DOT code on the sidewall
indicate the week of manufacture (the first two
numbers of the three-digit date code) followed
by the last number of the year.
The owner immediately admitted that the
vehicle slid on ice and hit a curb, damaging
the right rear tire and wheel. Both the tire and
wheel were replaced and the alignment
checked. The owner then dropped the price of
the vehicle $500! Knowing the date code helps
assure that fresh tires are purchased and can
also help the technician determine if the tires
have been replaced. For example, if new tires
are found on a vehicle with 20,000 miles, then
the technician should check to see if the
vehicle may have been involved in an accident
or may have more miles than indicated on the
odometer.
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James Halderman
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109 TIRES AND WHEELS
Figure 109-18
Typical DOT date code. This tire was built the sixth week of 2005.
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Figure 109-19
pressure sensor.
Cutaway of a run-flat tire showing the reinforced sidewalls and the required
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James Halderman
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109 TIRES AND WHEELS
Figure 109-20 A conventional tire on the left and a run-flat tire on the right, showing what
happens when there is no air in the tire.
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James Halderman
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109 TIRES AND WHEELS
TECH TIP: PAX Replacement
Tip In most cases, the
fastest and easiest approach to
follow if a PAX tire requires
replacement is to purchase a
replacement tire/wheel
assembly. While more
expensive than replacing just
the tire, this approach is often
used to help the vehicle owner
get back on the road faster
without any concerns as to
whether the replacement tire
was properly installed.
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Figure 109-21 The PAX run-flat tire system is composed of three unique components—a special
asymmetrical wheel, a urethane support ring, and special tire.
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James Halderman
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Figure 109-22 The Tire Performance Criteria (TPC) specification number is imprinted on the
sidewall of all tires used on General Motors vehicles from the factory.
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James Halderman
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109 TIRES AND WHEELS
FREQUENTLY ASKED QUESTION: What Is
a Low-Rolling-Resistance Tire? Lowrolling-resistance (LRR) tires reduce rolling
resistance, which is the power-robbing friction
between the tire and crown. The E-metric tire,
designated for use on electric or hybrid
vehicles, operates at higher inflation
pressures, reduced load percentages, and
lower rolling resistance. These tires were first
used on the GM EV1 electric vehicle.
To soften the ride of tires pumped with
additional air, a new tire profile was
developed. Narrower rim width and rounder
sidewalls make the tire more shock absorbent.
To make the tires roll more freely, low-rollingresistant tread compounds are molded into
smaller tread elements that flex easily and
with less friction when they touch the road.
LRR tires are available from most major tire
manufacturers, including Michelin the Energy
MXV4 Plus and Goodyear VIVA 2. According to
tire engineers, the basic tradeoff of low rolling
resistance is poor wet traction performance. To
improve wet road performance and traction
requires the use of more silica in the tread,
which increases the cost of the tire. Neither a
technician nor a vehicle owner can determine
the relative rolling resistance unless the tires
are compared using a coast-down test from
highway speed to zero or a laboratory testing
machine.
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James Halderman
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109 TIRES AND WHEELS
Figure 109-23 The size of the wheel is usually cast or stamped into the wheel. This wheel is 7
inches wide. The letter “J” refers to the contour of the bead seat area of the wheel.
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109 TIRES AND WHEELS
Figure 109-24 The wheel rim well provides a space for the tire to fit during mounting; the bead
seat provides a tire-to-wheel sealing surface; the flange holds the beads in place.
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Figure 109-25
A cross section of a wheel showing part designations.
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Figure 109-26 Offset is the distance between the centerline of the wheel and the wheel
mounting surface.
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109 TIRES AND WHEELS
Figure 109-27 Back spacing (rear spacing) is the distance from the mounting pad to the edge of
the rim. Most custom wheels use this measurement method to indicate the location of the mounting
pad in relation to the rim.
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109 TIRES AND WHEELS
Figure 109-28 Bolt circle is the diameter of a circle that can be drawn through the center of each
lug hole or stud. The bolt circle is sometimes referred to as PCD for pitch circle diameter.
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109 TIRES AND WHEELS
Figure 109-29 Measuring the bolt circle on a five lug wheel is difficult, but a quick and easy way
includes measuring as shown to determine the approximate bolt circle of a five-lug wheel.
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Figure 109-30 Measure center-to-center distance and compare the distance to the figures in the
chart in the text to determine the diameter for a five-lug bolt circle.
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FREQUENTLY ASKED
QUESTION: What Does This
Mark in a Wheel Mean? The
symbol JWL, for the Japan
Wheel Light Metal Standard
Mark, means that the wheel
meets the technical standards
for passenger-car light-alloy
wheels. See the mark in FIGURE 109–31 .
The manufacturer is
responsible for conducting the
inspections set forth in the
technical standard, and the
JWL mark is displayed on those
products that pass the
inspection.
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Figure 109-31
A typical JWL symbol for the Japan Wheel Light Metal standard mark.
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Figure 109-32 (a) A rubber snap-in style tire valve assembly. (b) A metal clamp-type tire valve
assembly used on most highpressure (over 60 PSI) tire applications such as is found on many
trucks, RVs, and trailers. The internal Schrader valve threads into the valve itself and can be
replaced individually, but most experts recommend replacing the entire valve assembly every time
the tires are replaced to help prevent air loss.
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Figure 109-33
Various styles of lug nuts.
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TIRE INSPECTION 1 Check the tire information placard, usually located on the driver’s door or
door jamb, for the specified tire size and inflation pressure.
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TIRE INSPECTION 2
Visually check the tires for abnormal wear or damage.
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TIRE INSPECTION 3
stem.
Remove the tire valve cap and visually check the condition of the valve
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TIRE INSPECTION 4 Check inflation pressure by pushing the tire pressure gauge straight onto
the end of the tire valve. If a “hissing” sound is heard, then the reading will not be accurate.
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TIRE INSPECTION 5 Read the pressure and compare to specifications. Use an analog or digital
gauge if possible which have been proven to be more accurate than a mechanical pencil-type gauge.
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TIRE INSPECTION 6
A typical tire tread depth gauge.
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TIRE INSPECTION 7 The blade of the tire tread depth gauge is pushed down into the groove of
the tire at the lowest part.
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TIRE INSPECTION 8 Remove the gauge from the tire and read the tread depth at the metal
housing. Tread depth is usually measured in 1/32’s of an inch.
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TIRE INSPECTION 9 If the top of Lincoln’s head is visible, then the tread depth is lower than
2/32 in., the legal limit in many states.
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