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REPAIR TIRE AND WHEEL
Competency Standard (SK) :
Repairmen Tire and Wheel
Basic Competency (KD)
1. Identify wheel and tire construction2. Check wheel3. Remove and install wheels4. Check tire5. Remove and install tires6. Tire and wheel balancing
Competency Achievement Indicators
1. Explain function of tire and wheel reffering to the text book
2. Type and characteristic of tire and wheel explained reffering to text book
3. Damage type of tire and wheel explained reffering to text book
4. Remove, install tire and wheel without damaging other ones and other system
5. Tire and wheel balancing according to Standard Operational Procedure (SOP)
Instructional Materials
The friction (traction) between the tire and the roaddetermines the handling characteristics of any vehicle.
The compounding, construction, and condition of tiresare some of the most important aspects of steering,suspension, alignment, and braking of any vehicle.
A vehicle that handles poorly, pulls, darts, jumps, orsteers “funny” may be suffering from defective orworn tires.
TIRE AND WHEEL
TIRES
Tires are mounted on wheels that are bolted to the vehicle toprovide the following:
1. Shock absorber action when driving over rough surfaces
2. Friction (traction) between the wheels and the road
Tires are available in many different designs and sizes.Understanding the construction of a tire is important for the techto be able to identify tire failure or vehicle handling problems.
All tires are assembled by hand from many different componentparts consisting of various rubber compounds, steel, and varioustypes of fabric material.
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PARTS OF A TIRE
Tread The part of the tire that contacts the ground is the tread.Tread rubber is chemically different from other rubber parts of atire. It is compounded for a combination of traction and tire wear.
Tread depth is usually 11/32 in. deep on new tires (this couldvary, depending on manufacturer, from 9/32 to 15/32 in.).
Figure 83–1 shows a tread depth gauge.
NOTE: A tread depth is always expressed in 1/32nds of an inch, even if
the fraction can be reduced to 1/16ths or 1/8ths.Continued
TIRE AND WHEEL
the groove of the tire. (b) The tread depth is read at the top edge of the sleeve. In this example, the
Figure 83–1 (a) A typical tire tread depth gauge. The center movable plunger is pushed down into
tread depth is 6/32 in.
(a) Wear indicators are also called wear bars.When tread depth is down to the legallimit of 2/32″, bald strips appear acrossthe tread.
(b)
See Figure 83–2.
Continued
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Figure 83–2 Wear indicators (wear bars) are strips of bald tread that show when the tread depthis down to 2/32 in, the legal limit in many states.
Continued
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Tie bars are molded into the tread of most all-season-rated tires,placed between tread blocks on outer tread rows to preventunusual wear and to reduce tread noise.
As the tire wears normally, the tie bars will gradually appear. Thisshould not be mistaken for an indication of excess outer edgewear. A solid band across the entire width of the tread is what theservice technician should consider the wear bar indicator.
Grooves, called circumferential grooves or kerfs, are large, deeprecesses molded in the tread and separating the tread blocks.Grooves running sideways across the tread lateral grooves.
See Figure 83–3.Continued
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Figure 83–3 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.
Continued
TIRE AND WHEEL
Grooves in both directions are necessary for wet traction. Trappedwater can actually cause the tires to ride up on a layer of water andlose contact with the ground, called hydroplaning.
Sipes are small slits in the tread area to increase wet and drytraction.
With worn tires, hydroplaning can occur at speeds as low as 30mph on wet roads. Stopping and cornering is impossible whenhydroplaning occurs.
See Figure 83-4.
Continued
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Figure 83–4 Hydroplaning can occur at speeds as low as 30 mph (48 km/h). If the water is deepenough and the tire tread cannot evacuate water through its grooves fast enough, the tire can belifted off the road surface by a layer of water. Hydroplaning occurs at lower speeds as the tire
becomes worn.
Continued
TIRE AND WHEEL
Sidewall The part of the tire between the tread and the wheel iscalled the sidewall. It contains all the size and construction detailsof the tire.
Some tires turn brown on the sidewalls after a short time due toozone (atmosphere) damage, which causes the rubber to oxidize.Premium-quality tires contain an anti-oxidizing chemical additiveblended with the sidewall rubber to prevent this discoloration.
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White Sidewall/Lettered On pneumatic tires constructed in theearly 1900s, natural rubber was used. The entire tire was white.
It was discovered that carbon black greatly increased the toughnessof a tire. The public did not like the change from white tires toblack, so manufacturers put the carbon black (lamp black) only inthe rubber that was to be used for the tread portion of the tire. Thistire lasted a lot longer because the black rubber tread was strongerand tougher; it sold well because the sidewalls were white.
White sidewall or white lettered tires contain a strip of whiterubber under the black sidewall, ground off at the factory to revealthe white rubber. Various widths of whitewalls are made possibleby changing the width of the grinding wheel.
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Bead The bead is the foundation of the tire and is located wherethe tire grips the inside of the wheel rim.
1. The bead is constructed of many turns of copper- orbronze-coated steel wire.
2. The main body plies (layers of material) are wrappedaround the bead.
3. Most radial-ply tires and all truck tires wrap the beadwith additional material to add strength.
CAUTION: If the tire bead is cut or damaged, the tire must be replaced!
Continued
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Body Ply A tire gets strength from the layers of material wrappedaround both beads under the tread and sidewall rubber. This creates
the framework, or “carcass,” of the tire; these body plies are often
called carcass plies.
Figure 83–5 Typical construction of a radialtire. Some tires have only one body ply, andsome tires use more than two belt plies.
A 4-ply tire has four layers of material.
If body plies overlap at an angle (bias), the tire is called a bias-ply tire.
If one or two body plies are used and lie directly from bead tobead, the tire is called radial ply.
Continued
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Belt A tire belt is two or more layers of material applied over thebody plies and under the tread area only, to stabilize the tread andincrease tread life and handling.
1. Belt material can consist of the following:
• Steel mesh • Fiberglass
• Aramid• Nylon
• Rayon
2. All radial tires are belted.
NOTE: Most tires rated for high speed use a nylon “overlay” or “cap
belt” between the 2-ply belt and the tread of the tire. This overlay helpsstabilize the belt package and helps hold the tire together at high speeds,when centrifugal force acts to tear a tire apart.
Continued
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Inner Liner The soft rubber lining (usually a butyl rubbercompound), the inner liner, protects the body plies and helpsprovide for self-sealing of small punctures.
Major Splice When the tire is assembled by a craftsperson on atire-building machine, the body plies, belts, and tread rubber arespliced together.
The fabric is overlapped approximately five threads. The pointwhere the majority of these overlaps occur is called the major
splice, which represents the stiffest part of the tire. This majorsplice is visible on most tires on the inside.
See Figure 83–6.
Continued
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Figure 83–6 The major splice of a tire canoften be seen and felt on the inside of thetire. The person who assembles (builds)the tire usually places a sticker near themajor splice as a means of identification
for quality control.
NOTE: On most new vehicles and/or new tires, the tire manufacturerpaints a dot on the sidewall near the bead, indicating the largest diameterof the tire. The largest diameter of the tire usually is near the major splice.The wheel manufacturer either marks the wheel or drills the valve corehole at the smallest diameter of the wheel. The dot should be aligned withthe valve core or marked for best balance and minimum radial runout.
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TIRE MOLDING After the tire has been assembledby the tire builder, it is called agreen tire.
At this stage in construction,the rubber can be returned andreused because it has not beenchanged chemically.
The completed green tire isplaced in a mold where itsshape, tread design, and allsidewall markings are formed.
Figure 83–7 Tire construction is performed byassembling the many parts of a tire together on a
tire-building machine. Continued
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Figure 83–8 After the entire tire has been assembled into a completed “green” tire, it is placedinto a tire-molding machine where the tire is molded into shape and the rubber is changedchemically by the heat. This nonreversible chemical reaction is called vulcanization.
While in the mold, a steambladder fills the inside of thetire and forces the tire againstthe outside of the mold.
After 30 minutes at 300°F(150°C), the heat changes thechemistry of the rubber.
The tire is no longer called agreen tire but a cured tire, andafter inspection and cleaning, itis ready for shipment.
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Why Do I Get Shocked By Static Electricity When IDrive 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 cannotconduct the static electricity to the ground, static electricity builds up insidethe vehicle and is discharged through the body of the driver and/orpassenger whenever the metal door handle is touched.
Newer tire sidewall designs that use silica usually incorporate carbonsections that are used to discharge the static electricity to ground. To helpreduce the static charge buildup, spray the upholstery with an antistatic
spray available at discount and grocery stores.
NOTE: Many “temporary use only” spare tires are constructed with
diagonal (bias) plies; the size designation is T for temporary.
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METRIC DESIGNATIONEuropean and Japanese tires use metric designations. The European size indicates exact physical size (width) of the tire and the speed ratings. European sizes also include the aspect ratio, eg., 185/70SR x 14. If the aspect ratio of a European-sized tire is not indicated, it is generally 83% for most radials.
In the chart, 185SR x 14 denotes the following:
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American Metric Tire Size Designations After 1980, tires in the US were also designated using the metric system.
P205/75R x 14
If a tire is a bias ply with a belt of additional material under the tread area, its size designation uses the letter B to indicate belted: P205/75B x 14.Some tires use letters at the end of the tire size (suffixes) to indicate special applications
TIRE AND WHEEL
How Much Does Tire Pressure Change With a ChangeIn Temperature?
As the temperature of a tire increases, the pressure inside the tire alsoincreases. The general amount of pressure gain (when temperaturesincrease) 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 thendriven on a highway, the tire pressure may increase 5 PSI or more.
Always check tire pressures on a vehicle that has been driven fewer than2 miles (3.2 km). Tire pressure also affects fuel economy. If all four tiresare underinflated (low on air pressure), fuel economy is reduced about 0.1mile per gallon (mpg) for each 1 PSI low. For example, if all four tires wereinflated to 25 PSI instead of 35 PSI, not only is tire life affected but fueleconomy is reduced by about 1 mile per gallon (10 0.1 1 mpg).
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CAUTION: DO NOT LET AIR OUT OF A HOT TIRE! If air isreleased from a hot tire to bring the pressure down to specifications, thetire will be underinflated when the tire has cooled. The tire pressurespecification is for a cold tire.
TIRE AND WHEEL
How Much Bigger Can IGo? - Part 1
Many owners think they can improve their vehicle by upgrading the tire sizeover the size that comes from the factory to make their vehicle look sportierand ride and handle better. When changing tire size, 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. An original equipment tire size 205/75 x 15 (outside diameter 27.1 in.) can be changed to 215/75 x 15 (o.d. 27.6 in.). This much change is less than 1⁄2 in. in width and increases the outside diameter by 1/2 in.
TIRE AND WHEEL
How Much Bigger Can I Go?Part 2
Outside diameter is calculated by adding the wheel diameter to the cross-sectional height of the tire, multiplied by 2.
Figure 83–9 Notice that the overall outside diameter of the tire remains almost the same and at thesame time the aspect ratio is decreased and the rim diameter is increased.
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How Much Bigger Can I Go?Part 3
5. Whenever changing tires, make sure that the load capacity is thesame greater than that of the original tires.
6. If wider tires are desired, a lower aspect ratio is required tomaintain same, or close to the same, overall outside diameter of
the tire.
Old New
P205/75 x 15 P215/70 x 15205 x 0.75 = 154 mm 215 x 0.70 = 151 mm
Notice that the overall sidewall height is generally maintained. If larger tiresare needed, then 225/60 x 15s may be OK—let’s check the math:
225 x 0.60 = 135 mmNotice that this is much too short a sidewall height when compared with
the original tire (see no. 6).
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SERVICE DESCRIPTIONTires built after 1990 use a “service description” method of sidewall information.
Figure 83–10 Cross-sectional view of a typical tire showing the terminology.
In accordance with ISO 4000 (International Standards Organization), it includes size, load, and speed rating in one easy-to-read format.
Continued
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HIGH-FLOTATION TIRE SIZES
High-flotation tires for light trucks are designed to give improved off-road performance on sand, mud, and soft soil and still provide acceptable hard-road surface performance.
These tires are usually larger than conventional tires and usually require a wider-than-normal wheel width. High-flotation tires have a size designation such as 33 x 12.50R x 15LT :
Continued
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LOAD INDEX AND EQUIVALENT LOADSThe load index is an abbreviated method to indicate the load-carrying capabilities of a tire.The weights listed in the chart represent the weight that each tire can safely support. Multiply this amount by 4 to get maximum the vehicle should weigh fully loaded with cargo and passengers.
See Figure 83–11.
Continued
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Figure 83–11 Typical sidewall markings for load index and speed rating following the tire size.
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If I Have An Older Vehicle,What Size Tire Should I Use?
Newer radial tires can be used on older-model vehicles if the size of thetires is selected that best matches the original tires.
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SPEED RATINGS
Tires are rated according to maximum sustained speed. A vehicle should never be driven faster than the speed rating of the tires. As speed increases, fewer compromises exist for driver comfort and low noise level. The higher speed rating does not mean a better tire. To survive, a high-speed tire must be built with stiff tread compounds, reinforced body (carcass) construction, and fabric angles that favor high speed and high performance over other considerations.
A V-rated tire has less tread depth than a similar H-speed rated tire, and often not give as long of a service life. Speed ratings were first developed in Europe; letters correspond to metric speed in kilometers per hour.
Continued
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CAUTION: A high speed rating does not guarantee that the tires will
Not fail, even at speeds much lower than the rating. Tire condition, inflation, and vehicle loading also affect tire performance.
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Figure 83–12 The E.C.E. symbol on a sidewall of a tire. Notice the small -s at the end, indicatingthat the tire meets the “pass-by” noise limits.
Continued
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What Effect Does Tire Size Have on Overall Gear Ratio?Customers often ask what effect changing tire size has on fuel economyand speedometer readings. If larger (or smaller) tires are installed on avehicle, many other factors also will change. These include the following:
1. Speedometer reading. If larger-diameter tires are used, it will readslower than actual speed. This can result in speeding tickets!
2. Odometer reading. Even though larger tires are said to give betterfuel economy, the opposite can be calculated! Since a larger-tiretravels farther than a smaller-diameter tire, the larger tire will causethe odometer to read a shorter distance than the vehicle actuallytravels. If the odometer reads 100 miles traveled on tires 10%oversized, the actual distance traveled is 110 miles.
3. Fuel economy. If fuel economy is calculated on miles traveled, theresult will be lower fuel economy than for the same vehicle with the
original tires.
TIRE AND WHEEL
What Does The Little “E” Mean on the Sidewall? - Part 1
Most countries have government agencies that regulate standards formotor vehicles sold and/or driven within their jurisdiction. In the UnitedStates, the U.S. Department of Transportation and National HighwayTraffic Safety Administration are responsible for developing many of thenationwide standards for vehicles.
Tires that are certified by their manufacturers to meet U.S. standards arebranded with “DOT” (Department of Transportation) preceding the TireIdentification Code on their sidewall. In Europe, because so much personaland commercial travel extends beyond the borders of any one country, theEconomic Commission for Europe (E.C.E.) helps develop uniform motorvehicle standards for its member countries to regulate and standardizepassenger and commercial vehicle components.
While sound is a by-product of modern society, it’s one thing that mostEuropeans would enjoy less of. Excessive noise is considered a form ofenvironmental pollution readily apparent to humans.
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What Does The Little “E” Mean on the Sidewall? - Part 2The E.C.E. symbol on a tire’s sidewall identifies that the manufacturercertifies that the tire meets all regulations, including the load index andspeed symbol that appear in its service description. In order to be E.C.E.branded, tires must receive laboratory approval, pass confirmation testing,and have their manufacturing plant pass quality control inspections.
The letter “e” and the number codecombination (in a circle or rectangle)identify the country originally grantingapproval, followed by digits indicatingthe Regulation Series under which thetire was approved.
Tires that have also been tested andmeet the “pass-by” noise limits canhave a second E.C.E. brandingfollowed by an “-s” (for sound).
TIRE PRESSURE AND TRACTIONAll tires should be inflated to the specs given by the vehiclemanufacturer, written in the owner’s manual or on a placard orsticker on the door post or glove compartment.
Figure 83–13 A typical door placard usedon a General Motors vehicle indicating therecommended tire inflation. Note that theinformation also includes the tire size andspeed rating of the tire as well as therecommended wheel size.
The pressure number molded into the sidewall of a tire is themaximum pressure when the tire is cold. (Pressures higher thanstated on the sidewall may be measured on a hot tire.)
Continued
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TIRE CONICITY AND PLY STEER
Tire conicity can occur during the construction of any radial orbelted tire when the parts of the tire are badly positioned, causingthe tire to be smaller in diameter on one side.
Figure 83–14 Conicity is a fault in the tire that can cause the vehicle to pull to one side due to thecone effect (shape) of the tire.
When this tire is installedon a vehicle, it can causepull to one side of the roaddue to the cone shape ofthe tire.
Continued
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NOTE: Radial pull or radial tire pull are other terms often used to
Describe tire conicity.
Since the cause of conicity is due to the construction of the tire
itself, there is nothing the tech can do to correct the condition.
The exact cause of the conicity is generally due to the slightmovement of the belt and tread in the mold during inflation.
If a vehicle pulls to one side of the road, the service technicianshould switch tires left to right (left-side tires to the right sideand the right-side tires to the left side of the vehicle).
If this swap of tires corrects the pulling condition, tire conicity wasthe possible cause.
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Ply steer describes a slight pulling Figure 83–15 Notice the angle of thebelt material in this worn tire. The angleof the belt fabric can cause a “ply steer”or slight pulling force toward one side
of the vehicle.
force on a vehicle due to the angle
of the cords in the belt layers, not
in the ply layer of the carcass
(body), as the name implies.
Ply steer will cause a slight drift
regardless of its direction of rotation.
Switching tires left to right will not
correct a ply steer condition.
Ply steer is built into the tire during
construction; nothing can correct
ply steer, except compensate with
alignment angles.
Continued
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VEHICLE HANDLING AND TIRE SLIP ANGLE
All accelerating, braking, and cornering forces of a vehicle aretransferred to pavement at just four spots. The combined area ofthese four spots is about equal to the size of your opened textbook.
As a vehicle is turned, the wheels are moved while the tires remainin contact with the road. These actions “twist” the carcass of thetire and create a slip angle between the direction the wheel ispointing and the direction the tread is pointing.
Figure 83–16 Slip angle is theangle between the direction thetire tread is heading and thedirection it is pointed.
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RIM WIDTH AND TIRE SIZE
As a general rule, for a given rim width it is best not to changetire width more than 10 mm (either wider or narrower). For agiven tire width, it is best not to vary rim width more than 1/2 in.in either direction.
Installing a tire on too narrow a wheel will cause the tire to wearexcessively in the center of the tread. Installing a tire on too widea wheel will cause excessive tire wear on both edges.
See a tire store representative for recommended tire sizes that canbe safely installed on your rims.
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Is There a Rule of Thumb for Rim Size?According to the Tire and Rim Association, Inc., the answer is no. Each tiresize has a designated rim width on which it is designed to be mounted soas to provide the best performance and wear. The width of the specifiedrim 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 usedis to multiply the width of the rim by33.55 to determine the approximatetire size for the rim. For example,consider the information on the chart.
Always check with the tiremanufacturer as to the specified tirerim width that should be used.
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UNIFORM TIRE QUALITY GRADING SYSTEM
The U.S. Department of Transportation (DOT) and the National Highway Traffic Safety Administration (NHTSA) developed a system of tire grading, the Uniform Tire Quality Grading System (UTQGS), to help customers better judge the relative performance of tires.
Figure 83–17 Typical “Uniform TireQuality Grading System” (UTQGS)ratings imprinted on the tire sidewall.
The three areas of tireperformance are:
• Tread wear
• Traction
• Temperature resistance
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Tread Wear The tread wear grade is a comparison rating based
on the wear rate of a standardized tire, tested under carefullycontrolled conditions, which is assigned a value of 100 and a lifeof 20, 000 miles. A tire rated 200 should have a useful life twiceas long as the standard.
NOTE: All tires sold in the United States must have UTQGS ratingsmolded into the sidewall.
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Traction Traction performance is rated by the letters AA, A, B,and C, with AA being the highest.
The traction rating is only one of many other factors that affect wetbraking traction, including air inflation, tread depth, vehicle speed,and brake performance.
NOTE: The traction rating is for wet braking distance only! It does not
include cornering traction or dry braking performance.
Continued
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Temperature Resistance Is rated by the letters A, B, and C, withA being the highest rating.
Tires generate heat by rotating and flexing during normal driving.A certain amount of heat buildup is desirable because tiresproduce their highest coefficient of traction at normal operatingtemperatures. If temperatures rise too much, a tire can start tocome apart—the oils and rubber in the tire start to become aliquid!
Grade C is the minimum level that all tires must be able to passunder the current Federal Motor Vehicle Safety Standard No. 109.
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DOT TIRE CODE
All tires sold in the United States must be approved by the U.S.Federal Department of Transportation (DOT).
The DOT tire code requirements include resistance to tiredamage from curbs, chuckholes, and other occurrences for a tireused on public roads.
Each tire has a DOT number molded into the sidewall of thetire.This number is usually imprinted on only one side of the tireand is usually on the side opposite the whitewall.
NOTE: Most race tires are not DOT-approved and must never be usedon public streets or highways.
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The DOT code includes letters and numbers, such asMJP2CBDX264.
The first two letters identify the manufacturer and location. Forthis example, the first two letters (MJ) mean that the tire wasmade by the Goodyear Tire and Rubber Company in Topeka,Kansas. The last three numbers are the build date code.
The last of these three numbers is the year (1994), and the 26means that it was built during the 26th week of 1994. Startingwith tires manufactured after January 1, 2000, the tire build dateincludes four digits rather than three digits. A new code such as“3406” means the 34th week of 2006 (“3406”).
See Figure 83–18. Continued
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Figure 83–18 Typical DOT date code. This tire was built the sixth week of 2005.
Continued
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SPARE TIRES
Most vehicles today come equipped with space-saver spare tires toreduce the size and weight of the entire vehicle and increase fueleconomy. The style and type of these spare tires have changed agreat deal over the last several years, and different makes andtypes of vehicles use various types of spare tires.
CAUTION: Before using a spare tire, always read the warning label (if
so equipped) and understand all use restrictions. For example, some sparetires are not designed to exceed 50 mph (80 km/h) or be driven more than500 miles (800 km).
Continued
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Many small, space-saving spare tires use a higher-than-normal airinflation pressure, usually 60 psi (414 kPa).
NOTE: When was the last time you checked the tire pressure in your
spare tire? The spare tire pressure should be checked regularly.
Even though the tire often differs in construction, size, diameter,and width from the vehicle’s original tires, it is amazing that thevehicle usually handles the same during normal driving.
These tires are not constructed with the same durability as a full-size tire and should be removed from service as soon as possible.
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RUN-FLAT TIRES
Run-flat tires (abbreviated RFT) are designed to operate withoutany air for a limited distance (usually 50 miles at 55 mph).
A typical run-flat tire (also called extended mobility tire [EMT] orzero pressure [ZP] tire) requires the use of an air pressuresensor/transmitter and a dash-mounted receiver to warn the driverthat a tire has lost pressure. Due to reinforced sidewalls, thevehicle handles almost the same with or without air pressure.
See Figures 83–19 and Figures 83–20.
CAUTION: Tire engineers warn that rapid cornering should be avoidedif a run-flat tire has zero air pressure. The handling during quickmaneuvers is often unpredictable and could be dangerous.
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Figure 83–19 Cutaway of a run-flat tire showing the reinforced sidewalls and the requiredpressure sensor.
Continued
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Figure 83–20 A conventional tire on the left and a run-flat tire on the right, showing whathappens when there is no air in the tire.
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PAX Run-Flat Tires Michelin developed a run-flat tire that hasthree unique components:
A special wheel that has two bead seats that are ofdifferent diameters. The outside bead seat is 10 mmsmaller in diameter than the inside bead seat. Thismeans that a conventional tire cannot be installed ona PAX-style wheel.
A urethane support ring that is designed to supportthe weight of the vehicle in the event of a flat tire.
A special tire that is designed to operate without air.
See Figure 83–21.Continued
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Figure 83–21 The PAX run-flat tire systemis composed of three unique components—a special asymmetrical wheel, a urethanesupport ring, and special tire.
The PAX tire designhas a unique sizing:
Continued
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Servicing a PAX Wheel/Tire Assembly If a flat tire occurs orwhen a PAX tire becomes worn and requires replacement, specialcare should be taken to properly remove the tire from the wheel.
Because the urethane support ring prevents the tire bead fromentering the dropped center section of the wheel, the outside beadshould be broken from the wheel, and the support ring removedbefore the tire can be removed from the wheel.
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GENERAL MOTORS TPC RATINGAll General Motors original equipment (OE) tires have a rating that identifies the size as well as the tread design, wear, traction, and heat resistance factors. All of these factors are combined in a set of numbers and letters that is imprinted in the tire mold. This is referred to as the Tire Performance Criteria (TPC) rating.
Figure 83–22 The Tire PerformanceCriteria (TPC) specification number isimprinted on the sidewall of all tiresused on GM vehicles from the factory.
If a customer wants the same performance in a replacement tire, replace the tire with any brand of tire that has the same TPC identification.
Continued
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TIRE-PRESSURE MONITORINGSYSTEM (TPMS)
The Transportation Recall Enhancement, Accountability andDocumentation (TREAD) Act requires all vehicles be equippedwith a tire-pressure monitoring system that will warn the driver inthe event of an underinflated tire.
The National Highway Traffic Safety Administration (NHTSA)requires tire-pressure monitoring systems (TPMS) in passenger
vehicles and light trucks manufactured after November 1, 2003.
The requirement to equip vehicles with a tire-pressure monitoringsystem was phased-in starting in 2004 and requires that 100% of theaffected vehicles be equipped in 2007. Continued
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Indirect To help compensate for speed variation during cornering,an indirect tire pressure monitoring system checks the rotatingspeeds of diagonally opposed wheels. If the total is greater than apredetermined value, the TPMS warning light is illuminated. Thewarning lamp will stay on until air is added to the tire and theignition is cycled off and on.
NOTE: This system cannot detect if all of the tires are under inflated,
only if one tire is under inflated.
Continued
TIRE AND WHEEL
What Is a Low-Rolling Resistance Tire?Low-rolling-resistance (LLR) tires reduce rolling resistance, which is thepower-robbing friction between tire and crown. The E-metric tire, for use onelectric or hybrid vehicles, operates at higher inflation pressures, reducedloads and lower rolling resistance. First used on the GM EV-1 electric car.
To soften the ride of tires pumped with additional air, a new tire profile wasdeveloped. Narrower rim width and rounder sidewalls make the tire moreshock absorbent. To make the tires roll more freely, low-rolling-resistanttread compounds are molded into smaller tread elements that flex easilyand with less friction. LRR tires are available from most tire manufacturers,including Michelin the Energy MXV4 Plus and Goodyear VIVA 2.
TIRE AND WHEEL
TPMS SENSORSTire-pressure monitoring sensors can be of different designs:
Continuous-wave-type sensor designed to signal whenexposed to 5 to 7 seconds of continuous 125 KHz wave signal.
Magnetically-triggered-type sensor—designed to trigger atester if exposed to a powerful magnetic force.
Pulse-width-modulated-type sensor—designed to betriggered when exposed to modulated wave 125 KHz signal.
The sensor also can vary according to the frequency at which ittransmits tire-pressure information to the receiver in the vehicle.The two most commonly used frequencies are:
315 MHz
433.92 MHz (commonly listed as 434 MHz)Continued
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Check the TMPS Sensors Before and AfterService
It is wise to check that all of the tire-pressure monitoring system sensorsare working before beginning service work. For example, if the tires needto be rotated, the sensors will have to be reprogrammed for their newlocation. If a tire pressure monitoring sensor is defective, the procedurecannot be performed. Use an aftermarket or OEM tire-pressure monitoring
sensor tester, as shown here.
Then the tire-pressure sensorsshould be checked again after theservice to make sure that they areworking correctly before returningthe vehicle to the customer
Figure 83–25 A typical tire-pressuremonitoring system tester. The unit shouldbe held near the tire and opposite the valvestem if equipped with a wheel-mountedsensor, and near the valve stem if equippedwith a valve-stem-type sensor.
Programming the TPM Receiver Whenever the tires are rotatedor a new sensor has been installed, the TPM receiver must bereprogrammed to recognize the new sensor locations.
Failure to do so will result in pressure readings being incorrectlydisplayed on the driver information center. A scan tool will handlethis reprogramming task.
If no new sensors were installed, there is also a way to reprogramthe receiver without the scan tool. The wireless TPM receiver ishoused in the keyless entry system’s RF receiver.
Using the key fob to place the receiver in “program” mode, thesensor locations can be programmed with a special magnet.
See Figure 83–26.Continued
The magnet fits over the valve stem in a way that will force thesensor to turn itself on while stationary, allowing the receiver to“see” it and learn its location while in programming mode.
Figure 83–26A magnet is placed around thevalve stem to reprogram stem-mounted tire pressure sensors.
The special magnet tool and a scan tool are both needed when anew sensor has been installed.
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To reprogram the TPM after tire rotation on a GM vehicle withoutusing a scan tool:
With KOEO (key on, engine off), the “lock” and “unlock” buttonson the key fob should be simultaneously pressed and held. Thehorn will chirp, indicating the receiver is in programming mode.Programming must be completed within five minutes.
NOTE: If the horn does not chirp at the start of this procedure, the TPM
option has not been enabled. A scan tool is needed to enable the system.
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At the left front wheel, the special magnet tool must be held overthe valve stem to force the sensor to transmit its code. The hornwill chirp , indicating the TPM system has recognized the sensor.The next sensor must be programmed within one minute.
The remaining sensors should be programmed in the followingorder: RF, RR, LR. The horn will chirp when each sensor has been
detected; twice to indicate completion of programming.
NOTE: The technician should not replace either the OEM cap or thevalve stem with standard parts. Conventional valve stem parts will inhibitthe sensor’s ability to transmit its signal.
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How Can You Tell If The Vehicle Has a TPMS Sensor?If the tire/wheel assembly has a tire-pressure monitoring system (TPMS)valve type sensor, it can usually beidentified by the threaded portion ofthe valve stem. If the valve stem isblack rubber, then it does not have astem-mounted tire-pressure sensor.
However, the wheel may be equippedwith a wheel mounted sensor, so careshould be taken to avoid damagingthe sensor during service.Figure 83–27
A clear plastic valve-stem tire-pressure monitoringsensor, showing the battery on the right and theelectronic sensor and transistor circuits on the left.
TIRE AND WHEEL
TIRE SELECTION CONSIDERATIONS
Selecting the proper tire is very important for proper handling andsafety of any vehicle. Don’t select a tire by styling or looks alone.
CAUTION: If changing tire sizes or styles beyond the recommendationsas stated here, consult a knowledgeable tire store representative for help inmatching wheel and tire combinations to your vehicle.
NOTE: Some tires may be five or more years old when purchased.
Always check the date code!Continued
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TIRE SELECTION CHART
TIRE AND WHEEL
WHEELS
The concept of a wheel has not changed in 5,000 years, but thestyle and materials used have changed a lot. Early automotivewheels were constructed from wood with a steel band as the tire.
Today’s wheels are constructed of steel or aluminum alloy.Because early wheels used spokes that resembled a spider’s webthe center section of the wheel is called the center section or
spider. The rubber tire attaches to the rim of the wheel.
The rim has two bead flanges where the bead of the tire is heldagainst the wheel when the tire is inflated. The flange shape isimportant and is designated by Tire and Rim Association letters.
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For example, a wheel designated 14 x 6JJ means the diameter ofthe wheel is 14 in. and the wheel is 6 in. wide measured frominside to inside of the flanges. The letters JJ indicate the exactshape of the flange area.
Figure 83–28 The size ofthe wheel is usually cast orstamped into the wheel.This wheel is 5 1/2 in. wide.The letters JJ refer to thecontours of the seat area of
the wheel.
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TIRE AND WHEEL
This flange area shape and the angle that the rim drops down from the flange are important because of the following:
They permit a good seal between the rim and the tire.
They help retain the tire on the rim in the event of loss of air. This is the reason why modern wheels are called “safety rim wheels.”
Run-flat tires (tires that are designed to operate without air for a limited distance without damage) often require a specific wheel rim shape.
See Figure 83–29.Continued
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Figure 83–29 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.
Continued
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Wheel Offset
A very important variable in wheel design is offset.
If the center section (spider) is centered on the outer rim, the offset is zero.
Wheel offset is referred to as ET, German for Einpress Tieffe.
Figure 83–30 A cross section of a wheel showing part designations.
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Positive Offset The wheel has a positive offset if the centersection is outward from the wheel centerline. Front-wheel-drive vehicles use positive-offset wheels to improve the loading on the front wheels and to help provide for a favorable scrub radius.
Negative Offset The wheel has a negative offset if the centersection is inboard (or “dished”) from the wheel centerline. Avoid using replacement wheels that differ from original offset.
See Figure 83–31. Continued
TIRE AND WHEEL
Figure 83–31 Offset is the distance between the centerline of the wheel and the wheel mounting surface.
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Back Spacing
Also called rear spacing or backside setting, back spacing is the distance between the back rim edge and the wheel center section mounting pad.
This is not the same as offset.
Back spacing can be measured directly with a ruler, as shown at right:
Figure 83–32 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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Determining Bolt Circle On four-lug axles and wheels, the boltcircle measurement is taken from center to center on opposite studsor holes, as shown:
Figure 83–33Bolt 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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On five-lug axles and wheels, it is a little harder to determine bolt circle. One method is to measure from the far edge of one bolt hole to the center of the hole two over from the first, as shown:
Figure 83–34The easiest method to determine the approximate bolt circle of a five-lug wheel.
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Also for a five-lug wheel, measure from center-to-center between two adjacent studs and convert this measurement into bolt circle diameter, as in the chart shown.
Figure 83–35Measure 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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Steel Wheels The traditional wheel material, a steel wheel isvery strong due to its shape and that it is work hardened during manufacturing. Painting and baking cycles also increase the strength of a steel wheel. Steel wheels are formed from welded hoops that are flared and joined to stamped spiders.
Aluminum Wheels Forged and cast aluminum wheels arecommonly used on cars and trucks. Forged means hammered or forged under pressure into shape. A forged aluminum wheel is much stronger than a cast wheel.
Aluminum wheels are thicker than steel and when balancing, coated or covered wheel weights should be used to prevent galvanic corrosion damage. Most use an alloy of aluminum, with copper, manganese, silicon, or other elements to achieve physical strength and characteristics for the exact product.
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Some racing wheels are made from a lighter-weight metal called magnesium. These wheels are called mag wheels (an abbreviation for magnesium).
True magnesium wheels are not practical for production wheels because their cost and corrosion are excessive compared with steel or aluminum alloy wheels.
The term mag wheel, however, is still heard when referring to alloy (aluminum) wheels.
NOTE: If purchasing replacement aftermarket wheels, check that they
are certified by the SFI. SFI is the Specialty Equipment Manufacturers Association (SEMA) Foundation, Incorporated. SEMA and SFI are non-government agencies that were formed by the manufacturers themselves to establish standards for safety.
What Does This Mark On a Wheel Mean?The symbol JWL, for the Japan Wheel Light Metal Standard Mark, means the wheel meets the technical standards for passenger-car light-alloy disk wheels. 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.
Figure 83–36A typical JWL symbol for the Japan Wheel Light Metal Standard Mark.
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TIRE VALVES
All tires use a Schrader valve to hold air. The valve was invented in New York in 1844 by August Schrader for the Goodyear Brothers: Charles, Henry, and Nelson. Today, Schrader valves are used not only as valves in tires but on fuel-injection systems, air-conditioning systems, and air shock (ride control) systems.
Most experts agree the valve stem should be replaced whenever tires are replaced. A defective or leaking valve stem is a major cause of air loss. Low tire pressure can cause the tire to become overheated. Aluminum (alloy) wheels often require special metal valve stems that use a rubber washer and are actually bolted to the wheel.
See Figure 83–37.
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Figure 83–37 (a) A rubber snap-in style tire valve assembly. (b) A metal clamp-type tire valve assembly used on most high-pressure (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.
(a) (b)Continued
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UNSPRUNG WEIGHT
The lighter the wheel and tire assembly, the faster it can react to bumps and dips in the road surface and thus the better the ride. It is the purpose of the suspension system to isolate the body of the vehicle from the road surface.
The wheel and tire are unsprung weight because they are not supported by the vehicle’s springs. Every time the vehicle hits a bump, the wheel is forced upward. Heavy mass of the wheesl and tires would transmit this force through the spring of the vehicle.
A much lighter wheel and tire assembly reacts faster to bumps and dips in the road surface. The end result is a smoother-riding vehicle with greater control.
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NOTE: Putting oversized tires on an off-road-type vehicle is extremely dangerous.
The increased unsprung weight can cause the entire vehicle to leave the ground after hitting a bump in the road. The increased body height necessary to clear the larger tires seriously affects drive shaft angles and wheel alignment angles, making the vehicle very difficult to control.
An aluminum wheel is generally lighter than the same-size stamped steel wheel. This is not always the case, however, so before purchasing aluminum wheels, check their weight!
TIRE AND WHEEL
LUG NUTS
Lug nuts are used to hold a wheel to the brake disc, brake drum, or wheel bearing assembly. Some models of VW, Audi, and Mazda use a lug bolt that is threaded into a hole in the brake drum or bearing assembly.
Typical lug nuts are tapered so the wheel stud will center the wheel onto the vehicle. The taper, usually 60 degrees, forms a wedge that helps ensure that the lug nut will not loosen. Steel wheels deform slightly when the lug nut is torqued down against the mounting flange; be certain that the taper is toward the vehicle.
Many alloy wheels use a shank-nut-type lug nut that has straight sides without a taper. Figure 83–38 shows several of the many styles of lug nuts that are available. Continued
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Figure 83–38 Various styles of lug nuts.
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Size Lug nuts are sized to the thread size of the stud onto which
they screw. Diameter and number of threads per inch are stated. Some vehicles use left-hand threads. RH and LH are commonly stated, indicating “right-hand” and “left-hand” threads.
A typical size is 7/16-20RH, where 7/16 indicates the diameter of the wheel stud and 20 indicates that there are 20 threads per inch. A common fractional size is 1/2 x 20.
Metric sizes such as M12 x 1.5 use a different sizing method.Other commonly used metric lug sizes include M12 x 1.25 and M14 x 1.5. Obviously, metric wheel studs require metric lug nuts.
NOTE: Some aftermarket manufacturers offer a stud conversion kit to replace the lug bolt with a conventional stud and lug nut.
TIRE AND WHEEL
PHOTO SEQUENCE Tire Inspection Step-By-Step
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(cont.)
PHOTO SEQUENCE Tire Inspection
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WHEEL AND TIRE DIAGNOSIS AND REPAIR
Proper tire service is extremely important for the safe operation of any vehicle.
Premature wear can often be avoided by checking and performing routine service, such as frequent rotation and monthly inflation checks.
4
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Figure 84–1 Using soapy water from a spray bottle is an easy method to find the location of an air leak from a tire.
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WHEEL MOUNTING TORQUEFor wheel mounting torque, make certain the wheel studs are clean and dry, and torqued to the manufacturer’s specifications.CAUTION: Most vehicle manufacturers also specify that the wheelstuds/nuts should not be lubricated with oil or grease. The use of a lubricant on the threads could cause the lug nuts to loosen.
Always tighten lug nuts gradually in a star pattern (tighten one nut, skip one, tighten the next nut).
This helps prevent warping the brake drums or rotors, or bending a wheel.
Figure 84–13 Always tighten wheel lug nuts (or studs) in a star pattern to ensure even pressure on the axle flange, brake rotors or drums, and the wheel itself.
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If exact torque value is not available, use the following chart as a guide for usual value based on the size (diameter) of the lug studs.
When you install a brand new set of aluminum wheels, retorque the wheels after the first 25 miles. Soft aluminum often compresses slightly, loosening the torque on the wheels.
TIRE AND WHEEL
Many factory-installed and aftermarket wheels use antitheft wheel lug nuts, usually on only one wheel stud. When removing or installing a locked lug nut, be sure the key is held square to the lug nut to prevent damaging either the nut or the key.
Figure 84–14 Most manufacturers recommend using hand tools rather than an air impact wrench to remove and install lock-type lug nuts to prevent damage. If either the key or the nut is damaged, the nut may be very difficult to remove!
TIRE AND WHEEL
Fine Tune Handling with Tire-Pressure Changes
The handling of a vehicle can be changed by changing tire pressures between the front and rear tires.
Understeer—A term used to describe how a vehicle handles when cornering where additional steering input is needed to maintain the corner, or resisting turning into a corner. This is normal handling for most vehicles.
Oversteer—A term used to describe handling where correction whilecornering is often necessary because the rear tires lose traction before the front tires.
Tire Pressure To Decrease To DecreaseUndersteer Oversteer
Front Tire Inflation Pressure Increase DecreaseRear Tire Inflation Pressure Decrease Increase
I Thought the Lug Nuts Were Tight!
Proper wheel nut torque is critical, as one tech discovered when a customer returned complaining of a lot of noise from the right rear wheel. Seen here is photo of what the tech discovered. The lug (wheel) nuts had loosened and ruined the wheel.
Figure 84–16This wheel was damaged because the lug nuts were not properly torqued.
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TIRE ROTATION
For long life and even tire wear, tire rotation is essential. Some rear-wheel-drive vehicles may show premature tire wear on the front tires, usually on the outer tread row.
This wear usually appears as a front-to-back (high and low) wear pattern on individual tread blocks. These blocks of tread rubber are deformed during cornering, stopping, and turning. This type of tread block wear can cause tire noise and/or tire roughness.
For best results, tires should be rotated every 6,000 miles or every six months. For suggested methods of rotation, such as the modified X, see Figure 84–17 .
TIRE AND WHEEL
Figure 84–17 The method most often recommended is the modified X method. Using this method, each tire eventually is used at each of the four wheel locations. An easy way to remember the sequence, whether front wheel drive or rear wheel drive, is to say to yourself, “Drive wheels straight, cross the nondrive wheels.”
TIRE AND WHEEL
Tire Rotation
Tire rotation should be done at every other oil change. Most manufacturers recommend changing the engine oil every 3,000 miles (4,800 km) or every three months; tire rotation is recommended every 6,000 miles (9,600 km), or every six months.
NOTE: Radial tires can cause a radial pull due to their construction. Ifwheel alignment is correct, attempt to correct a pull by rotating the tires front to rear or, if necessary, side to side.
Some tire manufacturers do not recommend rotating the tires on front-wheel-drive vehicles because the front tires often wear three times as fast as the rear. They recommend replacing just front tires, because the rear tires often last over 90,000 miles (145,000 km).
TIRE INSPECTIONAll tires should be carefully inspected for faults in the tire itself or for signs that something may be wrong with the steering or suspension systems of the vehicle.
Figure 84–18 Tire showing excessive shoulder wear resulting from underinflation and/or high-speed cornering.
See Figure 84–19 & 84–20 for more examples of common problems.
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Figure 84–19 Tire showing excessive wear in the center, indicating over- inflation or heavy acceleration on a drive wheel.
Figure 84–20 Wear on the outside shoulder only is an indication of an alignment problem.
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RADIAL RUNOUT
Though a tire has no visible faults, it can be the cause of vibration. If vibration is felt above 45 mph, regardless of the engine load, the cause is usually an out-of-balance or a defective out-of-round tire.
Both of these problems cause a tramp or up-and-down-type vibration. If the vibration is seen in the hood of the vehicle or felt in the steering wheel, then the problem is usually the front tires. If the vibration is felt throughout the entire vehicle or in the seat of your pants, then the rear tires (or drive shaft, in rear-wheel- drive vehicles) are the problem.
This can be checked by using a runout gauge and checking for radial runout.
TIRE AND WHEEL
To check radial runout (checking for out-of-round) and lateral runout (checking for side-to-side movement), follow these steps:
1. Raise the vehicle so that the tires are off the ground approximately 2 in. (5 cm).
2. Place the runout gauge against the tread of the tire in the center of the tread and, while rotating the tire, observe the gauge reading.
3. Note that maximum radial runout should be less than 0.060 in. (1.5 mm). Little, if any, tramp will be noticed with less than 0.030 in. (0.8 mm) runout. If the reading is over 0.125 in. (3.2 mm), replacement of the tire is required.
4. 4. Check all four tires.
TIRE AND WHEEL
Figure 84–21 A tire runout gauge being used to measure the radial runout of a tire. Figure 84–22 To check wheel radial runout,
the dial indicator plunger tip rides on a horizontal surface of the wheel, such as the bead seat.
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LATERAL RUNOUTTires can cause a type of vibration called shimmy. This rapid back-and-forth motion can be transmitted to the steering wheel.
Excessive runout is usually noticeable by the driver of the vehicle as a side- to-side vibration, especially at low speeds. Shimmy can be caused by an internal defect of the tire or a bent wheel.
Check for lateral runout. The maximum allowable reading is 0.045 in. (1.1 mm). If close to or above 0.045 in. (1.1 mm), check on the edge of the wheel to see if the cause of the lateral runout is due to a bent wheel, as shown in Figure 84–23.
Most manufacturers specify a maximum lateral runout of 0.035 in. (0.9 mm) for alloy wheels and 0.045 in. (1.1 mm) for steel wheels. See Figure 84–24.
TIRE AND WHEEL
Figure 84–23 To check lateral runout, the dial indicator plunger tip rides on a vertical surface of the wheel, such as the wheel flange.
Figure 84–24 The most accurate method of measuring wheel runout is to dismantle the tire and take dial indicator readings on the inside of the wheel rim.
TIRE AND WHEEL
Correcting Lateral Runout Excessive lateral runout may be corrected by one of several methods:
1. Re-torque the wheel in the proper star pattern to the specified torque. Unequal or uneven wheel torque can cause excessive lateral runout.
2. Remove the wheel and inspect the wheel mounting flange for corrosion or any other reason that could prevent the wheel from seating flat against the brake rotor or drum surface.
3. Check the condition of the wheel or axle bearings. Looseness in the bearings can cause the wheel to wobble.
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TIRE BALANCING
Proper balance is important for tire life, ride comfort, and safety. Tire balancing is needed due to lack of uniform weight, stiffness (at splices) and a combination of wheel runout and tire runout.
Balancing a tire can compensate for most of these conditions; If a tire or wheel is excessively out of round or bent, then replacement of the wheel or tire is required.
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Static Balance The term static balance means that the weightmass is evenly distributed around the axis of rotation.
1. For example, if a wheel is spun and stops at different places witheach spin, then the tire is statically balanced.
2. If the static balance is not correct, wheel tramp-type(vertical shake) vibration and uneven tire wear can result.
3. Static balance can be tested with the tire stationary or whilebeing spun to determine the heavy spot (sometimes calledkinetic balance).
TIRE AND WHEEL
Dynamic Balance The term dynamic balance means that thecenterline of weight mass is in the same plane as the centerlineof the wheel.
1. Dynamic balance must bechecked while the tire and thewheel are rotated, to determineside-to-side as well as up-and-down out of balance.
2. Incorrect dynamic balancecauses shimmy. Shimmy-typevibration causes the steeringwheel to shake from side to side.
Figure 84–25 A wheel balancer detects heavy spotson the wheel and tire, and indicate where to placeweight to offset both static and dynamic in balance.
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Prebalance Checks Before attempting to balance any tire, the
following should be checked and corrected:
1. Check the wheel bearing adjustment for looseness or wear.2. Check the radial runout.3. Check the lateral runout.4. Remove stones from the tread.5. Remove grease or dirt build-up on the inside of the wheel.6. Check for dragging or misadjusted brakes.7. Check for loose or backward lug nuts.8. Check for proper tire pressures.9. Remove all of the old weights.
10. Check for bent or damaged wheel covers.Continued
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Figure 84–26 An assortment of wheel weights designed to fit different shaped rims.
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The Vibrating Ford Van - Part 1
A tech was asked to solve a vibration problem on a rear-wheel-drive Fordvan. During a test-drive, the vibration was felt everywhere—the dash, thesteering wheel, the front seat, the shoulder belts; everything was vibrating!The tech balanced all four tires on a computer balancer. Even thoughwheel weights were put on all four wheels and tires, the vibration was even
worse than before.The tech rebalanced all four wheels time after time, but the vibrationwas still present. The shop supervisor then took over the job of solvingthe mystery of the vibrating van. The supervisor balanced one wheel/tireassembly and then tested it again after installing the weights. The
balance was way off!The supervisor broke the tire down and found about 1 quart (1 liter) ofliquid in the tire! Liquid was found in all four tires. No wonder the tirescouldn’t be balanced! Every time the tire stopped, the liquid would settlein another location. The customer later admitted to using a tire stop-leak
liquid in all four tires.
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The Vibrating Ford Van - Part 2
Besides stop leak, another common source of liquid in tires is water thataccumulates in the storage tank of air compressors, which often getspumped into tires when air is being added. All air compressor storagetanks should be drained of water regularly to prevent this from happening.
Figure 84–27Liquid tire stop leak was found inall four tires. This liquid causedthe tires to be out of balance.
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3. Stick-on weights come with an adhesive backing that is mostoften used on alloy wheels.
Figure 84–28 Stick-on weights areused from the factory to balance thealloy wheels of this Prowler.
Don’t Use Stop Leak in TPMS-Equipped Tires
Stop leak should never be used in a tire that is equipped with the TPMSsensor because the sensor can be damaged.
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Most wheel weights come in 1/21-ounce (0.25-oz) incrementsSee the chart on Page 1045of your textbook.
Use a wheel weight pliersto help ensure properinstallation and removalof wheel weights.
Figure 84–29 Wheel weight pliersare specially designed to removeand install wheel weights.
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How Much is Too Much Weight?Whenever balancing a tire, it is wise to use as little amount of weight aspossible. For most standard-size passenger vehicle tires, most expertsrecommend that no more than 5.5 oz of weight be added to correct animbalance condition. If more than 5.5 oz is needed, remove the tire fromthe wheel (rim) and carefully inspect for damage to the tire or the wheel.If the tire still requires more than 5.5 oz and the wheel is not bent or
damaged, replace the tire.
Bubble Balancer This type of static balancer is commonly usedand is accurate, if calibrated and used correctly. A bubble balanceris portable and can be easily stored away when not in use. It is alsoeasy to use and is relatively inexpensive.
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Computer Balancer The most popular type of tire balancer isthe computer dynamic balancer. Most computer balancers aredesigned to balance wheels and tires off the vehicle.
Computer dynamic balancers spin the tire at a relatively slowspeed (approximately 20 mph). Sensors attached to the spindle ofthe balancer determine the amount and location of weightsnecessary to balance the tire dynamically.
All computer balancers must be programmed with the actual rimsize and tire location for the electronic circuits to calibrate therequired weight locations.
Some computer balancers can perform loaded radial force andlateral force variation testing on the tire/wheel assembly anddisplay corrective actions. See Figure 84–30.
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Most computer balancers will be accurate to within 1/4 oz (0.25oz), while some are accurate to within 1/8 oz (0.125 oz).
Figure 84–30 A tire balancer that can alsodetect radial and lateral force variation andinstruct the operator where to rotate the tire toachieve the best ride, or indicate a bent wheel.
For sensitive drivers or vehiclesused for high speeds, such asracing, most computer balancerscan be programmed to balancewithin 1/8 oz (0.125 oz).
oz (150 gm) be used to balance
Most vehicle manufacturersspecify that no more than 5.5
any tire, with no more than 3.5oz (100 gm) used per side ofeach wheel.
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Are the Brake Drums and Rotors Balanced?Whenever an off-the-vehicle computer balancer is used, a question oftenasked by beginning techs is, “What about the balance of the brake drumsand rotors?” Brake drums and rotors are balanced at the factory, usually to
within 0.5 oz-in.Imbalance measured in oz-in. means any imbalance force is measured inounces, multiplied by the distance from the center measured in inches.This means that at a distance of 1 in. from the center of the drum or rotor,it is within 0.5 ounce of being perfectly balanced.Being within 0.5 ounce inch also means that at 5 inches from the center,the imbalance is only 0.1 ounce. What this means to the tech is that mostdrums and rotors are balanced well enough not to be a problem when
using off-the-vehicle balancers.However, the smart tech should look for evidence that weights have beenremoved from brake drums to permit aluminum wheels to fit, or other caseswhere the factory balance of the drums and rotors has been changed.
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REPLACEMENT WHEELS
Whenever a replacement wheel is required, the same offset shouldbe maintained. If wider or larger-diameter wheels are to be used,consult a knowledgeable wheel or tire salesperson to determinethe correct wheel for your application.
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CAUTION: Never remove the weights that are welded to the surface of
the brake drum facing the wheel. If replacement wheels do not fit withoutremoving these weights, either replace the brake drum (one without aweight) or select another brand or style of wheel. Removing the weightsfrom a brake drum can cause severe vibration at highway speeds.
Figure 84–31Most brake drums do not havethis much attached weight.
TIRE AND WHEEL
It Happened to Me—It Could Happento You
During routine service, I rotated tires on a Pontiac Trans Am. Everythingwent well and I even used a torque wrench to properly torque all of the lugnuts. Then, when I went to drive the car out of the service stall, I heard a
horrible grinding sound.
When I hoisted the car to investigate,I discovered that the front wheelswere hitting the outer tie rod ends.The 16-in. wheels had a differentback spacing front and rear, andtherefore these wheels could not berotated. Always check replacementor aftermarket wheels for proper fitbefore driving the vehicle.
Figure 84–32Notice that the rim touches the tie rod end.
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What are HubcentricWheels?
Most wheels are designed to fit over and be supported by the axle hub.Some wheels use an enlarged center hub section and rely on wheel studsfor support and to keep the wheel centered on the axle. Some aftermarketwheels may be designed to fit several different vehicles. As a result, thewheel manufacturers use plastic hubcentric adapter rings.
(a)
(b)Figure 84–33
(a) A hubcentric plastic ring partially removed from an aftermarket wheel.(b) A hubcentric plastic ring left on the hub when removing a wheel..
TIRE AND WHEEL
TIRE REPAIR
Tread punctures, nail holes, or cuts up to 1/4 in. (2.6 mm) can berepaired. Repairs should be done from the inside of the tire usingplugs or patches. With the tire off the wheel, inspect the wheel andthe tire for hidden damage.
The proper steps to follow for a tire repair are as follows:
1. Mark the location of the tire on the wheel.
2. Dismount the tire; inspect and clean the punctured area with aprebuff cleaner. DO NOT USE GASOLINE!
3. Buff the cleaned area with sandpaper or a tire-buffing tool untilthe rubber surface has a smooth, velvet finish.See Figure 84–34. Continued
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Figure 84–34 The area of the repair should bebuffed slightly larger than the patch to be
applied.
4. Ream the puncture with afine reamer from theinside. Cut and removeany loose wire materialfrom the steel belts.
5. Fill the puncture withcontour filling material,and cut or buff the materialflush with the inner linerof the tire.
6. Apply chemicalvulcanizing cement andallow to dry.
Continued
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7. Apply the patch and use astitching tool from centertoward the outside of thepatch to work any air outfrom between the patchand the tire.
Figure 84–35 A stitching tool being used toforce any trapped air out from under the patch.
Figure 84–36 A rubber plug being pulledthrough a hole in the tire. The stem is thencut off flush with the surface of the tire tread.
Another excellent tire repairprocedure uses a rubber plug.Pull the stem through the holein the tire, as shown.
Continued
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7. Remount the tire on the rim, aligning the marks made in step 1.Inflate to the recommended pressure and check for air leaks.
There are many tire repair products on the market. Always followthe installation and repair procedures exactly per themanufacturer’s instructions.
CAUTION: Most experts agree that tire repairs should be done from the
inside. Many technicians have been injured and a few killed when the tirethey were repairing exploded as a steel reamer tool was inserted into thetire. The reamer can easily create a spark as it is pushed through the steelwires of a steel-belted tire. This spark can ignite a combustible mixture ofgases inside the tire caused by using stop leak or inflator cans. Since thereis no way a technician can know if a tire has been inflated with a productthat uses a combustible gas, always treat a tire as if it could explode.
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Dispose of Old Tires Properly
Old tires cannot be thrown out in the trash. They must be disposed ofproperly. Tires cannot be buried because they tend to come to the surface.They also trap and hold water, which can be a breeding ground formosquitoes. Used tires should be sent to a local or regional recyclingcenter where the tires will be ground up and used in asphalt paving orother industrial uses. Because there is often a charge to dispose of oldtires, it is best to warn the customer of the disposal fee.
NOTE: Most vulcanizing (rubber) cement is highly flammable. Use out
of the area of an open flame. Do not smoke when making a tire repair.
Open-End Wrenches Make It Easier
Tire repair is made easier if two open-end wrenches are used to hold thebeads of the tire apart. See step 4 in the tire repair photo sequence.
PHOTO SEQUENCE Tire Mounting Step-By-Step
Continued
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(cont.)PHOTO SEQUENCE Tire Mounting
Continued
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(cont.)PHOTO SEQUENCE Tire MountingTIRE AND WHEEL
PHOTO SEQUENCE Tire Repair Step-By-Step
Continued
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(cont.)PHOTO SEQUENCE Tire RepairTIRE AND WHEEL
SUMMARY
1. For safety and proper vehicle handling, all four tires of thevehicle should be of the same size, construction, and type,except where specified by the manufacturer, such as on somehigh-performance sports cars.
2. Wheels should always be tightened with a torque wrench tothe proper torque in a star pattern.
3. Tires should be rotated every 5,000 to 7,000 miles (8,000 to11,000 km), or at every other oil change.
Continued
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SUMMARY (cont.)
4. Wheels should be cleaned around the rim area whenever tiresare changed and carefully inspected for cracks or other defectssuch as excessive lateral or radial runout.
5. Properly balanced tires prolong tire life. Wheel tramp or an upand-down type of vibration results if the tires are statically outof balance or if the tire is out-of-round.
6. Dynamic balance is necessary to prevent side-to-sidevibration, commonly called shimmy.
7. Only coated or stick-on-type wheel weights should be used onalloy wheels to prevent corrosion damage.
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END
