CHAPTER 27 Servicing Wheels 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 Introduction (2 of 3) Poorly maintained wheels and tires: Decrease effective handling, fuel economy, ride quality Increase potential for accidents or breakdowns 1
Introduction (3 of 3) Wheels and tires can help identify other problems. Wear patterns on a tire correlate with damage to particular components. 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. 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. 2
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. 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. Principles (4 of 13) 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 3
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. 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 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 4
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 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. 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. 5
Principles (12 of 13) Center of gravity Balance point of vehicle Depends on location of engine and transmission Located above road and between tires 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 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 6
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. 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 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. 7
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 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 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 8
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 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 Wheels and Tires (10 of 49) Wheel studs and lug nuts Fasten wheels to rims Stressed by loads and forces Heat-treated, highgrade alloy steel 9
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. 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 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. 10
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. 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 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 11
Tires Hollow, donutshaped Provide traction and cushion Tire s air supports vehicle s mass. Tread provides frictional contact with road surface. Wheels and Tires (17 of 49) 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 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 12
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 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 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. 13
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. Wheels and Tires (24 of 49) Tire valve stems, cores, and caps Valves are openings allowing inflation. Consist of valve stem with valve core 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 14
Wheels and Tires (26 of 49) Tire construction Bias-ply and radial types Radial is most common. 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 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 15
Wheels and Tires (29 of 49) Radial tires (cont d) Bracing layer placed under tread to strengthen and stabilize Fabric or steel, placed at 12-15 degrees to circumference line Links cord loops together Stabilizes when accelerating/braking Prevents cord movement when cornering 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 Wheels and Tires (31 of 49) Tread designs Varied tread patterns = different applications Directional Nondirectional Symmetric Asymmetric Directional and asymmetric 16
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 Wheels and Tires (33 of 49) Nondirectional tread patterns Mounted for any direction of rotation General applications Wheels and Tires (34 of 49) Symmetric tread patterns Same tread pattern on both sides Usually nondirectional Can be fitted in either direction 17
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 Wheels and Tires (36 of 49) Directional and asymmetric tread patterns Rotates in only one direction One side must face outward to ensure performance. 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. 18
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 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 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. 19
Wheels and Tires (41 of 49) Tire width measured in millimeters Sidewall to sidewall When inflated and without load Varies by manufacturer 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. 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 20
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 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 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 21
Wheels and Tires (47 of 49) Ratings are based on standardized test conditions. UTQG ratings for a given design may differ. 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. 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. 22
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. Tire Safety Features (2 of 16) Tire pressure monitoring systems Proper pressure is essential for safety and performance. Decreases fuel consumption Reduces CO 2 emissions Extends tire life 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. 23
Tire Safety Features (4 of 16) TPMS Monitors tire pressure Increases safety Decreases fuel consumption Improves performance Can be fitted to all vehicles 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 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 24
Tire Safety Features (7 of 16) Tire pressure monitoring: direct (cont d) Separate unit Uses band/strap to hold sensor Sensor opposite valve stem 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 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 25
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. 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 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 26
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 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. 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 27
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 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. Tire Service (2 of 22) Perform wheel alignment occasionally. Abnormal tire wear Steering/suspension parts replaced Handles/drives incorrectly After an accident 28
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 Tire Service (3 of 22) 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. 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. 29
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 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. 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 30
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 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. 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. 31
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 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. Tire Service (13 of 22) Balanced in three ways Static Dynamic Road force Tire Service (14 of 22) 32
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 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 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 33
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. 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. 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. 34
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 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. 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. 35
Maintenance and Repair (2 of 25) Tools Appropriate tools and equipment are needed. 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 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 36
Maintenance and Repair (5 of 25) Using a tire pressure gauge Two types Fixed workshop gauge Portable pocket-size gauge 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 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 37
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 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. Maintenance and Repair (10 of 25) Common wear patterns Feathering One-sided wear Cupping Center wear Edge wear 38
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. 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. 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. 39
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 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 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. 40
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. 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. 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 41
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. 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 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 42
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. 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. Maintenance and Repair (25 of 25) Water immersion method Leak will be obvious by discharge of bubbles. 43
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. 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. 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 44
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) 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 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 45
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. 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. 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. 46
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. 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. 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). 47
Credits Unless otherwise indicated, all photographs and illustrations are under copyright of Jones & Bartlett Learning. 48