1. CHAPTER 27
Servicing Wheels

2. Introduction (1 of 3)
Wheel and tire assembly is contact point between vehicle and road.
Vehicle rests on wheels and tires.
Determines handling and ride
Poorly maintained wheels and tires:
Decrease effective handling, fuel economy, ride quality
Increase potential for accidents or breakdown

3. Introduction (2 of 3) Poorly maintained wheels and tires:
Decrease effective handling, fuel economy, ride quality
Increase potential for accidents or breakdowns

4. Introduction (3 of 3)
Wheels and tires can help identify other problems.
Wear patterns on a tire correlate with damage to particular components.

5. Principles (1 of 13) Tires and wheels allow vehicle to roll.
Tires: little rigidity
Flex and deform when forced
Wheels: rigid, cannot absorb unevenness of road
Low coefficient of friction would make traction almost nonexistent.
Combo provides directional control, flexibility, traction.

6. Principles (2 of 13) Passenger vehicles have pneumatic tires.
Filled with pressurized air, which gives support
Forklifts use solid rubber tires.
Not susceptible to punctures
Early tires called tube-typed
Inner tube inside tire to seal in air
Recent vehicles use tubeless tires.
Tight seal to wheel prevents air leak.

7. Principles (3 of 13) Air pressure gives tire shape. Inflated to 32 psi
Approximately 51,200 lb of force
Tires do not expand like balloons due to reinforcing strands.
High pressure stiffens tire to support vehicle.

8. Principles (4 of 13) Tire distortion
Centrifugal force produces side force during cornering.
Side force: Pressure pushes wheel toward outside/inside of rim during turns.
Friction prevents force from pushing vehicle sideways.

9. Principles (5 of 13)
Tires provide opposing forces by distorting while gripping road.
Tire exerts cornering force due to tire’s elasticity.
Pulls distorted rubber back to normal position

10. Principles (6 of 13)
Tire’s sideways distortion makes vehicle follow path at an angle to road wheel.
Called slip angle
Slip angle increases as cornering force increases.

11. Principles (7 of 13)
Slip angle and cornering force increase as vehicle is driven into turn with decreasing radius, until tire slides.
Only resistance from sliding kinetic friction
Only grips again when vehicle slows or stops turning sharply
When slide force is reduced

12. Principles (8 of 13) Vehicle’s path is determined by:
Steering of front tires
Slip angles of both front and rear tires
Depend on vehicle’s weight distribution, wheelbase, tire track, vehicle length
Engine location affects weight
Front- or rear-wheel drive also a factor

13. Principles (9 of 13) During cornering
More weight on outside wheels from centrifugal force
Acceleration: more weight on rear wheels
Deceleration: more weight on front wheels
Centrifugal force pushes vehicle away from corner.
Resisted by cornering force of tires

14. Principles (10 of 13)
Slip angles are unequal due to acceleration, deceleration, cornering forces.
Understeer: front slip angles larger than rear slip angles
Vehicle “pushes” in corners.
Front of vehicle is pushed to outside of corner.
Oversteer: rear slip angles larger than front slip angles
Vehicle is “loose” in corners.
Rear slides toward outward corner.

15. Principles (11 of 13) Slip angles uneven (cont’d) Neutral steer
Both front and rear tires have equal amounts of slip angle.
Vehicle goes in direction front tires are pointing.

16. Principles (12 of 13) Center of gravity Balance point of vehicle
Depends on location of engine and transmission
Located above road and between tires

17. Principles (13 of 13) Center of gravity (cont’d)
Point through which all centrifugal force acts during cornering
Position determined by weight distribution
Closer to front on rear-wheel vehicles
Every vehicle has static weight distribution.
Changed laterally by centrifugal force when turning
Changed in fore-and-aft direction during acceleration and deceleration

18. Wheels and Tires (1 of 49)
Made of pressed steel or cast aluminum alloy
Lightweight, but strong
Alloy
Lighter than steel
Dissipates heat more effectively

19. Wheels and Tires (2 of 49) Terms wheel and rim used synonymously
Rim is outer circular lip of metal where tire is mounted.
Rim holds and seals tire to wheel.

20. Wheels and Tires (3 of 49)
Rim width: distance across rim flanges at bead seat
Bead seat: at edge of rim, creates seal between tire bead and wheel
Rim flange: exterior lip holding tire in place
Rim diameter: distance across center from bead seat to bead seat

21. Wheels and Tires (4 of 49)
Passenger vehicle wheel rims use drop-center design.
Inner section lower than sides
Allows tire removal/fitting
Made in one piece and fastened to wheel disc
Drop center for mounting and demounting tire
Tire is locked to rim when inflated.

22. Wheels and Tires (5 of 49)
Drop center can be closer to front or rear of wheel.
Closer to front in stock wheels
Closer to rear in deep dish wheels
Tire should be removed from this side

23. Wheels and Tires (6 of 49)
Manufacturers and legislators say passenger cars and light trucks must have safety-type drop-center.
Ridge/hump at inside edge of bead ledges
Holds tire beads in place when tire goes flat
Prevents tire from moving into well during blowout

24. Wheels and Tires (7 of 49) Made of two sections of pressed steel
Flange or disc drilled for wheel fasteners and rim
Passenger vehicles usually have steel-disc type.
Solid with holes to reduce weight and allow cooling
Welded/riveted to rim
Bolted to axle/axle flange

25. Wheels and Tires (8 of 49) Wheel offset
Distance from hub mounting surface to centerline of wheel
Brings tire centerline into close alignment with larger inner wheel bearing
Reduces load on stub axle
Requires space inside wheel assembly for brakes

26. Wheels and Tires (9 of 49) Offset can be:
Zero: plane of hub mounting surface even with centerline of wheel
Positive: plane of hub mounting surface shifted from centerline toward outside or front of vehicle
Negative: hub mounting surface toward brake side or back of wheel’s centerline

27. Wheels and Tires (10 of 49) Wheel studs and lug nuts
Fasten wheels to rims
Stressed by loads and forces
Heat-treated, high-grade alloy steel

28. Wheels and Tires (11 of 49)
Threads between studs and nuts are closely fitted and accurately sized.
Nuts must be tightened to correct torque with proper sequence.
If not, wheel could break off hub.

29. Wheels and Tires (12 of 49) Correct wheel stud must be used.
Tapered seat: tapered end toward rim, fit into matching taper in rim to help center wheel
Flat seat with washer: flat where it contacts wheel, washer on lug nut enabling turn independent from hex
Flat seat without washer: flat where it contacts wheel, no washer

30. Wheels and Tires (13 of 49)
Wheel inner hub mating surfaces and axle flange mounting face must be clean.
Wheel retaining nuts holding wheel to vehicle are torqued.
Recheck within a few days or 100 miles.
Stud can break due to overstressing.

31. Wheels and Tires (14 of 49) Retaining nuts (cont’d)
Most are right-hand threaded.
Tighten when turned clockwise.
Some use left-hand nuts/studs on right, and right-hand nuts/studs on left of vehicle.
Properly torqued lug nuts do not loosen up.

32. Wheels and Tires (15 of 49) Wheel center has holes for lug studs.
Machined hole in center
Centers wheel rim on axle
Provides required offset from centerline of wheel to face of mounting flange

33. Wheels and Tires (16 of 49) Bolt pattern
Number and spacing of lug nuts/wheel studs on wheel hub on wheel rim
Number determines pattern

34. Wheels and Tires (17 of 49) Tires Hollow, donut-shaped
Provide traction and cushion
Tire’s air supports vehicle’s mass.
Tread provides frictional contact with road surface. 34

35. Wheels and Tires (18 of 49) Tire is made of:
Tread: exterior rubber portion that contacts road
Plies/cords: reinforcing material that allows tread and sidewall to hold shape
Sidewalls: lightly reinforced sides that provide later strength to prevent ballooning 35

36. Wheels and Tires (19 of 49) Tire is made of (cont’d):
Inner liners: covering of casing material, seals air
Bead: bands of steel wire coated in rubber that give bead area stiffness to hold bead against bead seat and seal wheel rims

37. Wheels and Tires (20 of 49)
Tires are mostly composed of synthetic rubber with carbon black.
Adds strength and toughness
Long life
Stronger than natural rubber 37

38. Wheels and Tires (21 of 49)
Cords of synthetic strands or fabric have high tensile strength.
Measure of innate strength
Cord characteristics
Resist stretching
Flexible under load
Parallel and impregnated with rubber to form plies/belts 38

39. Wheels and Tires (22 of 49) Plies High strength in one direction
Flexible in other directions
Newer cords use fewer plies.
Increase flexibility
Higher number makes tire’s response to bumps harsher, but withstands punctures better. 39

40. Wheels and Tires (23 of 49)
Beads are composed of high-tensile steel coated with rubber.
Ply ends wrap around beads, then are wrapped in rubber.
Stops chafing of plies and seals bead against rim
Wire length of bead determines rim diameter.
Belts reinforce tread area. 40

41. Wheels and Tires (24 of 49) Tire valve stems, cores, and caps
Valves are openings allowing inflation.
Consist of valve stem with valve core 41

42. Wheels and Tires (25 of 49)
Valve stem is rubber or steel piece attaching valve to tire rim.
Valve core is Schrader valve.
Valve stem cap keeps debris out of valve stem.
Removed to check air pressure

43. Wheels and Tires (26 of 49) Tire construction
Bias-ply and radial types
Radial is most common. 43

44. Wheels and Tires (27 of 49) Bias-ply is used on off-road vehicles.
Body-ply cords extended diagonally from bead to bead at 30- and 40-degree angles
Successive plies laid at opposing angles
Strong, stable casing
Stiff sidewalls 44

45. Wheels and Tires (28 of 49)
Radial tires have ply cords laid across tread from bead to bead.
Better steering control
Used by most passenger cars
Use two or more layers of casing plies with cord loops
Sidewalls more flexible because casing plies do not cross over each other 45

46. Wheels and Tires (29 of 49) Radial tires (cont’d)
Bracing layer placed under tread to strengthen and stabilize
Fabric or steel, placed at degrees to circumference line
Links cord loops together
Stabilizes when accelerating/braking
Prevents cord movement when cornering 46

47. Wheels and Tires (30 of 49) Radial tires (cont’d)
Cord plies flex and deform only above road contact patch.
Properly inflated tire runs cool, increasing tread life.
Has rolling resistance, increasing fuel economy 47

48. Wheels and Tires (31 of 49) Tread designs
Varied tread patterns = different applications
Directional
Nondirectional
Symmetric
Asymmetric
Directional and asymmetric 48

49. Wheels and Tires (32 of 49) Directional tread patterns
Mounted to provide maximum moisture dissipation
Mounted to revolve in direction to correspond with tread pattern 49

50. Wheels and Tires (33 of 49) Nondirectional tread patterns
Mounted for any direction of rotation
General applications 50

51. Wheels and Tires (34 of 49) Symmetric tread patterns
Same tread pattern on both sides
Usually nondirectional
Can be fitted in either direction 51

52. Wheels and Tires (35 of 49) Asymmetric tread patterns
Different tread pattern from one side of tire to other
Good grip traveling straight and in turns 52

53. Wheels and Tires (36 of 49) Directional and asymmetric tread patterns
Rotates in only one direction
One side must face outward to ensure performance. 53

54. Wheels and Tires (37 of 49) A B C D E
Tread designs. A. Directional tread pattern. B. Nondirectional tread pattern. C. Symmetric tread pattern. D. Asymmetric tread pattern. E. Directional and asymmetric tread pattern. 54

55. Wheels and Tires (38 of 49) Tire markings Sizing and rating system
Manufacturer/brand name
ISO tire class, DOT compliance
Section width, aspect ratio
Tire construction type
Diameter, speed rating
Max pressure, load index 55

56. Wheels and Tires (39 of 49) Tire sizing and rating system (cont’d)
Uniform tire quality grading system
Tread wear grade
Traction grade
Temperature grade 56

57. Wheels and Tires (40 of 49) Tire sizes and designations
Appropriate for vehicle and use
Bead diameter must match rim diameter.
Section width must suit rim and be large enough for vehicle’s load-carrying capacity.
Tire must have clearance between body and chassis.

58. Wheels and Tires (41 of 49) Tire width measured in millimeters
Sidewall to sidewall
When inflated and without load
Varies by manufacturer

59. Wheels and Tires (42 of 49) Aspect ratio Height to width Percentage
Lower ratio means greater width in relation to height.
Higher ratio means smoother ride, more flex during cornering.

60. Wheels and Tires (43 of 49) Low-profile = short side wall
Difficult to remove and install
Aspect ratio as low as 25
Improves cornering performance, but not smooth
Higher speed rating

61. Wheels and Tires (44 of 49)
Tire ratings for tread wear, traction, temperature
Marked with UTQG
Obtained from tested tires on standardized test conditions
Higher number means longer life.
Based on normal conditions

62. Wheels and Tires (45 of 49) Traction grade is letter-based.
Based on tire’s ability to stop vehicle on wet asphalt and concrete in straight-line situation
Does not indicate cornering ability
Highest to lowest: AA, A, B, C

63. Wheels and Tires (46 of 49) Temperature grade
Letter based on test overseen by government
Measures how well tire stands up to and dissipates heat
Uses UTQG criteria
Graded from C to A

64. Wheels and Tires (47 of 49)
Ratings are based on standardized test conditions.
UTQG ratings for a given design may differ.

65. Wheels and Tires (48 of 49) Tire date of manufacture coding
DOT inspected
Must have manufacture date code on sidewall
3- or 4-digit code
Never use tires more than 6 years old.

66. Wheels and Tires (49 of 49) Codes are easy to read.
3 digits are used for tires from before 2000.
Tires manufactured in 90s may have triangle after number.
4 digits are used for tires from after 2000.

67. Tire Safety Features (1 of 16)
Flat tires are leading cause of breakdown.
Cannot drive on one or more flat tires
Most manufacturers use tire pressure monitoring systems.
Some use run-flat tires.
Some use self-sealing tires.
Some use spare tire/temporary tire.

68. Tire Safety Features (2 of 16)
Tire pressure monitoring systems
Proper pressure is essential for safety and performance.
Decreases fuel consumption
Reduces CO2 emissions
Extends tire life

69. Tire Safety Features (3 of 16)
Driving on underinflated tires can stress sidewalls.
Increased operating temperatures can cause premature tire failure.
Affects handling/performance
Can cause tire blowout or tread separation
All new passenger vehicles must have TPMS.

70. Tire Safety Features (4 of 16)
TPMS
Monitors tire pressure
Increases safety
Decreases fuel consumption
Improves performance
Can be fitted to all vehicles

71. Tire Safety Features (5 of 16)
Tire pressure: direct and indirect monitoring
Direct: measures via sensor in wheel, sends info wirelessly
Responds to drop as low as 2 psi
Sensor powered by internal battery
Either one-way or two-way communication
One-way: can only transmit to receiver
Two-way: can send and receive signals

72. Tire Safety Features (6 of 16)
Tire pressure monitoring: direct (cont’d)
Sensors inside tire and fastened to wheel
One-piece design with valve stem
Or separate unit screwed to valve stem

73. Tire Safety Features (7 of 16)
Tire pressure monitoring: direct (cont’d)
Separate unit
Uses band/strap to hold sensor
Sensor opposite valve stem

74. Tire Safety Features (8 of 16)
Tire pressure monitoring:
Indirect: most prevalent use wheel speed ABS to measure difference in wheels’ rotational speeds
Faster rotation, lower pressure

75. Tire Safety Features (9 of 16)
Run-flat tires
Maintain control during rapid pressure loss
Can last up to 50 mph for 50 miles
Cannot be driven with compromised or blown-out sidewall
Tire must be changed.
TPMS usually mandatory

76. Tire Safety Features (10 of 16)
Run-flat tires (cont’d)
Manufacturers say they save weight and space.
Do not need spare
Actually 2–3 times heavier
Unsprung weight affects suspension and can increase fuel consumption.

77. Tire Safety Features (11 of 16)
Run-flat tires (cont’d)
Extra materials during construction
More expensive
Harsher ride
Noisier
More storage space in trunk

78. Tire Safety Features (12 of 16)
Run-flat tires (cont’d)
Design features focus on rigidity and heat resistance.
Sidewall is thicker and made of reinforced rubber.
Carries weight at zero pressure

79. Tire Safety Features (13 of 16)
Run-flat tires (cont’d)
Bead shape same as conventional
Bead wire wider and reinforced
Uses special bead filler with low heat generation

80. Tire Safety Features (14 of 16)
Run-flat tires (cont’d)
Use EH2 rim technology
Double extended hump
Wider safety hump than standard rims
Tire bead has larger diameter.

81. Tire Safety Features (15 of 16)
Self-sealing tires
Recently introduced
Flexible and malleable lining
Seals once object removed
Can still leak, so require TPMS

82. Tire Safety Features (16 of 16)
Space-saver tires
Emergency use only
Cannot exceed 50 mph or 50 miles
Mini or collapsed, require inflation
Small with higher pressure

83. Tire Service (1 of 22) Periodic inspection ensures long life.
Check tire pressure.
Adjust if no TPMS.
Inspect tread area.
Inspect tread depth.
Inspect sidewalls.
Rotate tires.

84. Tire Service (2 of 22) Perform wheel alignment occasionally.
Abnormal tire wear
Steering/suspension parts replaced
Handles/drives incorrectly
After an accident

85. Tire Service (3 of 22) Proper tire inflation
Provides load-carrying capacity and affects performance
Based on load limit
Recommended cold inflation pressure
Tire placard on door frame, fuel filler flap, in glove compartment

86. Tire Service (4 of 22) Proper tire inflation (cont’d)
Max pressure on sidewall
Use a tire cage when inflating to prevent danger.
Check tires when cold for accuracy.
Cold: not driven for at least 3 hours or less than 1 mile
Driving produces heat, heats tires, heats air, expands, increases pressure.

87. Tire Service (5 of 22) Nitrogen fill
Oxygen is harmful to rubber and tire materials.
Reacts to rubber through oxidation
Loss of flexibility, sealing ability
Degradation over time
Pressure loss as inner liner oxidizes
Leaking results from rust/dust
Nitrogen reduces these problems.

88. Tire Service (6 of 22) Nitrogen fill advantages
Permeates rubber at slower rate
Far less reactive
Does not cause rust/corrosion or degrade rubber
Higher tire efficiency at correct pressure
Better maintains performance
Increases fuel efficiency
Reduces accidents

89. Tire Service (7 of 22) Air is 78% nitrogen, 21% oxygen, 1% other.
Nitrogen levels must be at least 95%.
2 or 3 inflations/deflations
Green valve stem caps indicate nitrogen.
Manufacturers do not mandate nitrogen use based on its ability to better retain consistent pressure.

90. Tire Service (8 of 22) Tire rotation pattern
Removal/relocation of each tire/wheel assembly
Promotes uniform wear
Extends tire life
Boosts fuel economy and performance
Recommended every 5000 miles or every oil change

91. Tire Service (9 of 22) Rotation sequence depends on:
Front-, rear-, all-wheel drive
Types of tires
If spare is involved
Four-tire rotation with nondirectional tires has one of 3 rotation patterns.
Forward-cross
Rearward-cross
X pattern

92. Tire Service (10 of 22) A B C D E F G
A. Forward-cross pattern. B. Rearward-cross pattern. C. X pattern. D. Front to-rear pattern. E. Side-to-side pattern from the other side of the vehicle. F. Five-tire forward-cross pattern. G. Five-tire rearward-cross pattern.

93. Tire Service (11 of 22) Wheel balance
Small imbalances from mass production
Not always perfectly round
Tolerance stacking
Tolerances stack up and wheel has balance and runout issues.

94. Tire Service (12 of 22) Imbalance produces uncomfortable vibration.
Permanent wearing of suspension/steering components
Uneven tire wear
Off balance when one section is heavier or stiffer than others

95. Tire Service (13 of 22) Wheels can be balanced on- or off- car.
Usually off-car
On-car if brake rotor, drum, hub out of balance
On-car means wheel needs rebalancing when rotated.

96. Tire Service (14 of 22) Balanced in three ways Static Dynamic
Road force

97. Tire Service (15 of 22) Static balancing
Imbalance measured when stationary
Does not consider width
Only considers weight
Assumes imbalance is centered across width
Static imbalance: tire moves up and down
No longer an acceptable method

98. Tire Service (16 of 22) Dynamic balancing When tire is rotating
Considers width
Dynamic imbalance: causes tires to move side to side and up and down
Places specific amounts of weight on each side of rim
Accounts for imbalance anywhere within tire/wheel assembly
Used in most shops today

99. Tire Service (17 of 22) Road force balancing
Road force imbalance: wheel balanced statically and dynamically, but still shakes
When wheel/tire not concentric or tire’s sidewall has uneven surface
Pushes up and down on vehicle
Provides best quality ride because it considers all balance factors

100. Tire Service (18 of 22) To dynamically balance:
Mount wheel/tire assembly on balance.
Spin up to speed to identify imbalance location and amount.
Balancer shows where/how much weight to add.
Spin wheel again to test.

101. Tire Service (19 of 22) To road force balance:
Run tire up against roller and measure uneven forces.
If encountered, machine will direct to rotate tire on wheel and spin again to check for concentricity issues.
Reinstall wheel.
Torque wheel nuts.

102. Tire Service (20 of 22) Top-quality tires hold balance well.
Sudden vibration could indicate lost balancing weight.
Vibration in steering wheel could indicate problem in front wheel.
Vibration in seat could indicate problem in rear tires.

103. Tire Service (21 of 22)
Different style wheel weights fit different rim configurations.
0.25-oz. increments
Are made of lead or are steel coated with zinc or other protective layer
Use new weights when balancing.
Old weight likely to be thrown

104. Tire Service (22 of 22) TPMS service Treat sensors with care.
If damaged, entire unit will need to be replaced.
Sealed component
Some powered by battery
Nickel-plated valve cores in aluminum valve stem
Never brass cores or unplated brass caps
Torque into place.
Use new sealing washers.

105. Maintenance and Repair (1 of 25)
Tires most maintenance-intensive
Regular inspections
Visually inspect every time vehicle comes into shop.
Check pressure monthly if no TPMS.
Rotate tires each oil change.

106. Maintenance and Repair (2 of 25)
Tools
Appropriate tools and equipment are needed.

107. Maintenance and Repair (3 of 25)
Equipment list:
Tire pressure gauge
Tread depth gauge
Valve stem tool
Tire dunk tank
Tire-changing machine
Tire spreader
Air tire buffer
Patch stitching tool
Tire inflation cage
Wheel balancing machine
Variety of wheel styles
Wheel weight hammer
TPMS reset tool

108. Maintenance and Repair (4 of 25)
Common tire and wheel issues
Air loss
Out-of-balance tire/wheel
Excessive loaded radial runout on tire/wheel/hub
Excessive lateral runout on tire/wheel/hub
Wheel trim imbalance (if fitted)
Heavy pulling

109. Maintenance and Repair (5 of 25)
Using a tire pressure gauge
Two types
Fixed workshop gauge
Portable pocket-size gauge

110. Maintenance and Repair (6 of 25)
Most popular pocket tire pressure gauges
Pencil type
Graduated sliding extension forced out of sleeve by air pressure
Dial type
Includes a graduated gauge and needle
Digital type
Gives digital reading and generally most accurate

111. Maintenance and Repair (7 of 25)
Measure pressure in psi, kPa, or bars.
1 bar = 14.5 psi = 100 kPa
Pressure varies in vehicles.
Recommended pressure on tire placard
Maximum pressure on sidewall

112. Maintenance and Repair (8 of 25)
Adjusting tire pressure
Must adjust periodically because tires lose air over time
Monthly
2008 and newer cars have TPMS
May have specific inflation and reset procedure
May be filled with nitrogen
Only use nitrogen unless emergency

113. Maintenance and Repair (9 of 25)
Checking for tire wear patterns
Patterns vary based on manufacturer and intended purpose.
Inspect regularly regardless of pattern.
Irregular wear patterns are indicative of problem.

114. Maintenance and Repair (10 of 25)
Common wear patterns
Feathering
One-sided wear
Cupping
Center wear
Edge wear

115. Maintenance and Repair (11 of 25)
Rotating tires
Helps to even tire wear
Extends life
Follow manufacturer’s recommendations.
Every oil change
Check brake lining thickness.
Look for leaks or damage to brake assembly.

116. Maintenance and Repair (12 of 25)
Dismounting a tire
Performed if:
Replacing old tires with new ones
Patching leaky tire
Switching between snow and regular
Only remove when necessary because it can damage sealing surface of bead.

117. Maintenance and Repair (13 of 25)
Dismounting is performed on machine.
Use extreme care.
Understand manufacturer’s specified procedure.
Turntable jaws grasp inside or outside of rim.
Alloy rim is clamped from outside.
Steel rim is clamped from inside.
Check instruction manual.

118. Maintenance and Repair (14 of 25)
Replacing a valve stem
Styles
Rubber press-fit valve stems: replaced when new tires mounted on rims
Screw-in valve stems: normally not replaced but may need to replace rubber washers or O-rings
TPMS sensor-integrated valve stems: may be part of valve stem or screw/snap on

119. Maintenance and Repair (15 of 25)
Know if TPMS sensor is connected to valve stem to avoid damage.
Can be damaged by trauma, scraping, improper tire changes
Easy and inexpensive to replace

120. Maintenance and Repair (16 of 25)
To change valve stem:
Wheel must be removed.
Deflate tire and break top bead.
On some vehicles, push down sidewall.
On others, remove tire from stem.
New rubber valve stem is installed with lubricant at base.

121. Maintenance and Repair (17 of 25)
Similar process for valve stems with threaded shank with locking nut and sealing washers
Remove wheel and deflate; break top bead.
Unscrew valve stem nut and remove stem.
Replace old sealing washers.
Reinstall valve stem.
Sometimes only valve stem core needs replacement.
Readjust tire pressure after installation.

122. Maintenance and Repair (18 of 25)
Mounting a tire
More than installing tire onto rim
Red dot at tire’s highest point, yellow dot at lightest
Red dot should line up with rim’s lowest point—match mounting.
Yellow dot should match up with heaviest point—weight matching.
These methods help avoid tolerance stacking.

123. Maintenance and Repair (19 of 25)
Type of tread affects direction of mount and on which side of vehicle.
Directional
Operate better in one direction, mount accordingly
Symmetric
Operate and mount in either direction
Asymmetric
Side specific, mount on specific rims

124. Maintenance and Repair (20 of 25)
Turntable jaws hold rim by grasping outside or inside.
Check instruction manual for correct clamping.
First time inflation is dangerous.
Some must be inflated in cage.
Always follow guidelines.

125. Maintenance and Repair (21 of 25)
Dismounting, inspecting, and remounting a tire on a wheel equipped with TPMS sensor
Requires special care
Mounted in two ways
Attached to valve stem or making it integral to valve stem
Using band fitting all around drop center of rim

126. Maintenance and Repair (22 of 25)
Dynamic balancing a tire
Balanced when spinning
Imbalanced when a spot on either inside or outside of centerline is heavy
Side-to-side imbalance when rotating, which causes vibration and shimmying
Result of manufacturer variations or damaged tire/wheel
Perform when new tires installed and when imbalance suspected

127. Maintenance and Repair (23 of 25)
Dynamic balancing a tire (cont’d)
Performed on a tire balancer capable of spinning tire and measuring location
Wear safety glasses.
Ensure safety hood is in place if present.
Requires specific wheel weights
Incorrect wheel weights can fly off when driven.
If directional, ensure installation in correct position.

128. Maintenance and Repair (24 of 25)
Inspecting the wheel assembly for air loss
Remove tire and air up to recommended pressure to check.
Preliminary check with spray bottle of soapy water around valve stem/core, bead area, tread area.
Soapy air bubbles will indicate problem.

129. Maintenance and Repair (25 of 25)
Water immersion method
Leak will be obvious by discharge of bubbles.

130. Diagnosis (1 of 6) Tire repair
Underinflation driving causes overheating and weakness on sidewall belts.
Dangerous, nonrepairable condition
Damage not visible from outside
If no signs of unrepairable failure, tire can be repaired using procedures recommended by a tire association.

131. Diagnosis (2 of 6)
Repairs from nails/similar object limited to tread area
Criteria for proper repair
Limited to tread area
Puncture injury no greater than ¼ʺ in diameter
Must remove tire from rim/wheel to inspect
Repairs cannot overlap.
Rubber stem/plug must be applied to fill puncture injury with patch applied to liner.

132. Diagnosis (3 of 6) Patching requires:
Tire machine to remove tire from wheel
Buffer to clean inside tire
Glue for attaching patch
Tire patch plug

133. Diagnosis (4 of 6) Measuring wheel, tire, axle flange, hub runout
Runout is side-to-side or up-and-down variation in wheel.
Only observed when driven
If primarily observed in steering column/hood, probably front wheel(s)
If vibration in entire vehicle, probably back wheel(s)

134. Diagnosis (5 of 6) Runout is defined as radial or lateral. Radial
Component is out of round or off center.
Felt as vertical vibration
Lateral
Component is bent or improperly manufactured.
Causes wheel to jiggle side to side
Horizontal vibration like a shimmy
Felt in steering wheel even at low speeds

135. Diagnosis (6 of 6) Inspecting, diagnosing, and calibrating TPMS
Inspections when tires dismounted
Diagnosis when system detects faults and turns on warning light
Calibration when tires rotated or sensor replaced

136. Summary (1 of 6)
Poorly maintained wheels and tires decrease effective handling and may lead to steering and suspension problems.
The main principles of understanding service of tires and wheels are: tire distortion, center of gravity, and wheel offset.

137. Summary (2 of 6)
Tire distortion refers to the tire’s cornering force countering the side force that occurs when a vehicle corners, to create a slip angle.
Center of gravity refers to the balance point of the vehicle, which is determined by location of the engine and transmission.
Wheel offset refers to the distance from the hub mounting surface to the centerline of the wheel.

138. Summary (3 of 6) Wheel offset can be zero, positive, or negative.
Tire and wheel assemblies must be balanced to prevent both static and dynamic imbalance.
Tire and wheel components include the wheel or rim, wheel studs and nuts, wheel center, and tires.
Rims usually have a deep well—a widened area on one side of the wheel.

139. Summary (4 of 6)
The design of passenger wheels is generally either well based or drop center.
Types of rims include: steel, one-piece alloy, two-piece alloy, multipiece alloy, custom, spinning, split, semi-drop well, drop well, and safety.
Wheel studs and lug nuts fasten the wheels to the rims.

140. Summary (5 of 6)
Wheel retaining studs or nuts can be tapered seat, flat seat with washer, or flat seat without a washer.
Tires provide the wheel with coverage and protection and absorb shock from road surfaces.
Tires are composed of treads, sidewalls, inner liners, and beads.

141. Summary (6 of 6)
Synthetic fabric cords are used to create plies, giving the tire strength and flexibility.
Tires are most commonly either cross-ply or radial (used by most passenger vehicles).

142. Credits
Unless otherwise indicated, all photographs and illustrations are under copyright of Jones & Bartlett Learning.