Parts of a Tire Tires
Contents
1. After studying this chapter you will be able to Identify the parts of a tire and wheel Describe different methods of tire construction Describe tire ratings Identify the parts of driving and nondriving hub and wheel bearing assemblies Explain tire and wheel sizes Correctly answer ASE certification test questions requiring a knowledge of tires wheels hubs and wheel bearings This chapter introduces the various tire wheel and hub designs used on modern vehic It explains how tires and wheels are constructed to give safe and depend able service The chapter also covers hub and wheel bearing construction for both rear and front wheel drive vehicles As a result you will be better prepared to study later chapters on brakes suspension systems and wheel alignment Tires Automobile tires perform two basic functions they act as a soft cushion between the road and the metal wheel and they provide adequate fraction friction with the road surface Tires must transmit driving braking and cornering forces to the road in both good and bad weather At the same time they should resist punctures and wear The tires used on early vehicles were solid rubber Today s automotive tires are pneumatic which means they are filled with air Internal air pressure pushes out on the inside of the tire to support the weight of the vehicle Today s vehicles use tubeless tires which do not have a s2. added to increase tread stiffness A radial ply tire has plies running straight across from bead to bead with stabilizer belts directly beneath the tread Tire markings on the sidewall of a tire give informa tion about tire size load carrying ability inflation pressure number of plies identification numbers quality ratings and manufacturer Tire size is given on the sidewall as a letter number sequence The aspect ratio or height to width ratio is a comparison of the tire s height and width The maximum load rating of a tire indicates the amount of weight the tire can carry at recom mended inflation pressure The maximum inflation pressure printed on the tire sidewall is the highest air pressure that should be pumped into the tire A tire speed rating is the maximum allowable sus tained road speed the tire can safely withstand without failure Some tires are self sealing seal small punctures because of a coating of sealing compound applied to the tire liner Retreads are old used tires that have had a new tread vulcanized applied using heat and pres sure to the old carcass or body Run flat tires have an extremely stiff sidewall construction so that they are still usable with a loss of air pressure A tire pressure monitoring system can detect low tire pressure and alert the driver if one or more tires is underinflated A drop center wheel is commonly used on pa senger vehicles because it allows for eas
3. con struction so that they are still usable with a loss of air pr sure If the tire leaks you can drive the vehicle to a repair shop without tire and wheel damage See Figure 65 10 The tire will retain most of its shape because the side wall is strong enough to support vehicle weight The tire uses a special rubber compound and a thick rubber sidewall support insert that helps support the weight of the vehicle Wear Bars Wear bars are used to indicate a critical amount of tread wear When too much tread has worn from the tires solid rubber bars will show up across the tread This tells the customer and the technician that tire replacement is needed Look at Figure 65 11 Tread wear indicators Figure 65 11 When wear bars are visible a tire is worn enough to be unsafe and should be replaced General Motors Chapter 65 Tire Wheel and Wheel Bearing Fundamentals 1247 Tire Pressure Monitoring Systems cases these sensors are attached to the tire valves In Many late model vehicles are equipped with tire other designs the sensors are held to the wheel with a pressure monitoring systems which alert the driver if metal or plastic strap See Figure 65 12 If the tire pres one or more of the vehicle s tires is underinflated There sure drops below a predetermined value the sensor on are two types of tire inflation systems used in late model the corresponding wheel will send a signal to a small vehicles direct systems
4. in the proper location so they rotate in the desired direction Spare Tires A spare tire or spare is an extra wheel and tire assembly that can be installed if the vehicle has a flat tire The spare can be a full tire or a compact tire A full size spare is a tire of the same size and type used on the other four wheels of the vehicle It can be mounted and used like any other tire It is being replaced by compact lighter spare tires Most new cars use a compact spare tire or space saver spare which is much smaller than the normal tire used on the vehicle It saves space in the trunk or storage area See Figure 65 8 A high pressure spare is a compact spare tire that holds higher than normal air pressure typically about 60 psi It is inflated when in the trunk and is ready for use Some spare tires are not inflated when in storage A small bottle of compressed air may be used to inflate the tire when needed A lightweight spare tire has very thin sidewall and tread construction Being light it can be more easily picked up and mounted on the vehicle However the driving range and maximum speed rating of a light weight spare are generally lower than those for a com pact spare 1246 Section 11 Suspension Steering and Brakes Special narrow Compact wheel spare tire Inflation pressure Figure 65 8 A compact spare tire is for temporary use only This one should be inflated to 60 psi 415 kPa It requires a
5. plies and ply rating For example the tire may be a 2 ply tire a 2 ply with a 4 ply rating plies made stronger than normal or a 4 ply tire A greater number of plies or a higher ply rating generally indicates a greater load carrying ability Sidewall Plies The number of sidewall plies is also shown on the tire sidewall DOT Serial Number DOT stands for Department Of Transportation When you see DOT on the tire sidewall the tire has passed prescribed safety tests Following the letters DOT is the DOT serial number which identifies the particular tire manufacturer plant location construction and date of manufacture The DOT serial number is stamped into the tire sidewall Tire Grades Tread wear traction and temperature grades are nor mally shown on the tire sidewall according to the Uniform Tire Quality Grading System Tread wear is given as a number Tread wear ratings range from 100 to 500 The higher the number the more resistant the tire is to wear Tire traction is given an A B or C rating A tire with an A rating would provide the most traction while a tire with a C rating would provide the least traction Tire temperature resistance is also given as an A B or C rating A tire with an A rating resists a temperature buildup better than a tire with a B or C rating Speed Rating A tire speed rating is the maximum allowable sustained road speed a tire can safely withstand without failure Speed ratings r
6. A and B D Neither A nor B 14 While discussing the basic parts of an automo tive wheel bearing Technician A says the bearing s outer race is sometimes pressed into the automobile s steering knuckle Technician B says a wheel bearing s outer race is some times pressed into the hub Who is right A A only B B only C Both A and B D Neither A nor B Technician A says a steering knuckle is a basic component in a driving hub and wheel bearing assembly Technician B says an inner drive axle is a basic component in a driving hub and wheel bearing assembly Who is right A A only B B only C Both A and B D Neither A nor B Activities Chapter 65 K Using a section of an old worn tire prepare a cutaway teaching aid showing the different parts and layers of the tire Prepare an overhead transparency that explains tire and wheel sizes and tire ratings As a classroom demonstration disassemble and identify the parts of a hub 3
7. September 1 2007 are equipped with a tire pressure monitoring system Wheels Wheels are designed to support the tire while with standing loads from acceleration braking and cornering Most wheels are made of steel A few optional types are cast aluminum or magnesium Refer to Figure 65 14 Mag wheels or mags is a nickname for aluminum or magnesium wheels These wheels do not need wheel covers See Figure 65 15 A drop center wheel is commonly used on pas senger vehicles because it allows for easier installation and removal of the tire Since the center of the wheel is smaller in diameter dropped than the rim the tire bead can fall into the recess Then the other side of the tire bead can be forced over the rim for removal See Figure 65 16 Wheel Tire z Lug stud Lug nut Drop center Figure 65 14 Cutaway shows many of the components relating to a wheel Mercedes Benz A standard wheel consists of the rim outer lip that con tacts tire bead and the spider center section that bolts to vehicle hub Normally the spider is welded to the rim Figure 65 17 illustrates the various dimensions of a wheel Compare this illustration with Figure 65 16 Figure 65 15 Aluminum or magnesium wheels are often called mags They do not need wheel covers Ford Lug bolt holes Pilot bore Spider center section Figure 65 16 Study the parts of this conventional drop center wheel Chap
8. and indirect systems receiver mounted in the passenger compartment The Direct tire pressure monitoring systems use a pres receiver then turns on a dash warning light to inform the sure sensor transmitter mounted at each wheel In some driver of the inflation problem See Figure 65 13 Wheel Pressure Sensor sensor transmitter Strap A B Figure 65 12 Some tire pressure monitoring systems use a pressure sensor transmitter mounted at each wheel A Valve mounted sensor B This sensor is strapped to the inside of the wheel Ford Chevrolet Dash Pressure display sensors Warning Pressure Warning Sensor Receiver Pressure light sensor chime signal sensor Figure 65 13 If one of the pressure sensor transmitters detects low tire pressure it will produce a radio signal A receiver in the passenger compartment detects the signal and triggers a warning light in the dash Toyota 1248 Section 11 Suspension Steering and Brakes In an indirect tire pressure monitoring system the anti lock brake system components are used to monitor tire pressure When pressure in a tire drops the tire s cir cumference is reduced This causes the wheel and tire assembly to spin faster than the other tires The computer interprets the speed sensor signal from the affected wheel as a drop in tire pressure and triggers a warning light A Note All vehicles with a gross vehicle weight rating of less than 10 000 Ib sold on or after
9. ange from B 31 mph or 50 km h to Z 149 mph or 238 km h It is important that the speed rating of a tire be higher than the speed at which the vehicle will be driven If too low a speed rating is used the tire could fail and cause a fatal accident This is extremely important if the vehicle is to be driven in areas where there is no speed limit some states and foreign countries 1245 Special Tires and Tire Features You should be familiar with several types of special tires and tire features The automotive technician will encounter compact spare tires self sealing tires retreads and run flat tires Asymmetric Tires Asymmetric tires have a different tread pattern on the inner edge than the outer edge The outer tread pattern is designed to improve cornering on dry surfaces The inner tread pattern is designed to improve traction on wet sur faces An asymmetric tire must be mounted so the proper edge faces the outside of the wheel This type of tire is generally marked with the word outside to indicate which way it should be mounted on the wheel Directional Tires Directional tires are high performance tires designed to rotate in a specific direction to minimize hydroplaning Hydroplaning is a loss of control that occurs when layer of water prevents the tire tread from contacting the road surface Directional tires have an arrow and the word rotation molded onto their sidewalls Care must be taken to mount directional tires
10. ch of the following is not a type of tire used on passenger cars A Radial B Bias ply C Lateral ply D Belted bias 6 What information is commonly given on the tire sidewall nN Chapter 65 Tire Wheel and Wheel Bearing Fundamentals A typical tire inflation pressure would be 22 psi 152 kPa True or False How does a self sealing tire work A n has small ridges that hold the tire on the wheel during a blowout Explain why a valve core is needed ____ are attached to the rim to balance the wheel and tire assembly and prevent vibration Name and describe the basic parts of a wheel bearing List and explain the nine basic parts of a hub and tapered roller bearing assembly List and explain the seven basic parts of a hub and ball bearing assembly A sealed hub and bearing assembly is not ser viceable True or False ASE Type Questions Technician A says one of the functions of an automotive tire is to provide a cushion between the road and the metal wheel Technician B says one of the functions of an automotive tire is to provide adequate traction with the road surface Who is right A A only B B only C Both A and B D Neither A nor B Technician A says automotive tires are pneu matic Technician B says modern automotive tires are not pneumatic Who is right A A only B B only C Both A and B D Neither A nor B Technician A says older veh
11. ea of the wheel and tire Hub and Wheel Bearing Assemblies Wheel bearings allow the wheel to turn freely around the spindle in the steering knuckle or in the bearing sup port Most wheel bearings are either tapered roller bear ings or ball bearings Figure 65 21 Bearing cage Inner race or cup Stationary or rotating shaft Stationary or rotating housing Outer race or cup A Wheel spider Hub Lug nut Press or Lug force fit Taper helps center wheel on hub Metric or left hand thread markings Lug nut Figure 65 20 A The lug nut screws onto a lug stud to secure the wheel to the hub The tapered end of the nut must contact the wheel The stud is pressed into the hub B If metric or left hand threads are used markings will normally be given on the nut or stud Cadillac The wheel bearings are lubricated with heavy high temperature grease This lets the elements rollers or balls operate with very little friction and wear Point contact Inner race or ring Shaft Housing Outer race or ring Figure 65 21 Two basic wheel bearing configurations A A tapered roller bearing has cylindrical rollers that operate between inner and outer races If the shaft is stationary the bearing will allow the outer housing or hub to turn If outer bearing mount is stationary the shaft or axle can turn in the bearing B Ball bearings are also used as wheel bearings espec
12. ed radial tire in 1948 radial tires were not standard on American vehicles until many years later In fact it was not until the gasoline crisis of the early 1970 s that American manufacturers began the switch to radial tires as a way to improve fuel economy By 1983 radial tires were standard equipment on all new American Passenger cars Summary e Automobile tires perform two basic functions they act as a soft cushion between the road and the metal wheel Tires must also provide adequate traction friction with the road surface e Car tires are pneumatic which means they are filled with air Front wheel bearing assembly A a Outboard 7 utboar Spi inner race Inboard inner Inboard race bearing Steering knuckle bearing support Figure 65 26 Disassembled view of a driving hub and wheel bearing assembly Study the names of the parts This type of assembly is commonly used on the front of front wheel drive vehicles However it can also be found on rear engine rear wheel drive sports cars Honda Section 11 Suspension Steering and Brakes Today s vehicles use tubeless tires which do not have a separate inner tube The tire and wheel form an airtight unit Tire rolling resistance is a measurement of the amount of friction produced as the tire operates on the road surface A bias ply tire has plies running at an angle from bead to bead A belted bias tire is a bias tire with belts
13. eparate inner tube The tire and wheel form an airtight unit Refer to Figure 65 1 Older vehicles used inner tubes soft thin leakproof rubber liners that fit inside the tire and wheel assemblies Tire Wheel and Wheel Bearing Fundamentals Parts of a Tire Although there are several tire designs all tires have the same basic parts Figure 65 2 e Beads wo rings that are made of steel wire and encased in rubber They hold the tire sidewalls snugly against the wheel rim e Body plies Rubberized fabric and cords wrapped around the beads They form the carcass or body of the tire e Tread Outer surface of the tire that contacts the road Sidewall Outer part of the tire that extends from the bead to the tread Markings on the sidewall provide information about the tire e Belts Sometimes used to strengthen the body plies and stiffen the tread They lie between the tread and plies e Liner Thin layer of rubber that is bonded to the inside of the plies It provides a leakproof mem brane for the modern tubeless tire Tubeless tire and wheel form leakproof unit Air pressure pushes outward Metal wheel to inflate tire Rubber tire Figure 65 1 With tubeless tires the tire and wheel form a leakproof unit Air pressure pushes outward on the inside of the tire 1241 1242 Section 11 Suspension Steering and Brakes Tread Body plies Liner Figure 65 2 Study the basic pa
14. for the front or rear of a car Two tapered roller bearings allow the hub and wheel to revolve around the stationary spindle Grease partially fills the hub to lubricate the bearings An inner seal prevents the loss of grease A nut on the end of the spindle allows adjustment of the bearing preload DaimlerChrysler 1251 Grease seal seal that prevents the loss of lubri cant from the inner end of the spindle and hub e Safety washer flat washer that keeps the outer wheel bearing from rubbing on and turning the adjusting nut e Spindle adjusting nut nut that is threaded on end of the spindle for adjusting the wheel bearing e Nut lock thin slotted nut that fits over the spindle adjusting nut e Cotter pin soft metal pin that fits through a hole in the spindle adjusting nut and nut lock to keep the adjusting nut from turning in service e Dust cap metal cap that fits over the outer end of the hub to keep grease in and road dirt out of bearings Since this hub and wheel bearing assembly does not transfer driving power the spindle is stationary It simply extends outward and provides a mounting place for the wheel bearings hub and wheel When the vehicle is moving the wheel and hub spin on the bearings and spindle The hub simply freewheels The hub is partially filled with grease to lubricate the bearings Figure 65 23 shows a disassembled view of a non driving front bearing and hub assembly Compare these pa
15. front of rear wheel drive cars or the rear of front wheel drive vehicles Florida Dept of Voc Ed e Steering knuckle or bearing support steering e Grease seal prevents lubricant loss between the or suspension component that holds the wheel inside of the axle and the knuckle or bearing bearings axle stub shaft and hub support Figure 65 26 shows an exploded view of another type of driving hub and wheel bearing assembly Compare it to Figure 65 25 e Driving hub mounting place for the wheel transfers driving power from the stub axle to the wheel e Axle washer special washer that fits between Other Hub and Wheel Bearing Assemblies the hub and locknut Modern vehicles use a wide variation of hub and Hub or axle locknut nut that screws on the end wheel bearing assemblies For example many late model of the drive axle stub shaft to secure the hub and vehicles use a sealed hub and bearing assembly that con other parts of assembly tains either ball bearings straight roller bearings or Freewheel or locking hub ring 4 Flange Stationary Driving and gasket spindle axle Inner bearing 5 Hub with disc Thrust assembly washer washer Figure 65 24 This front hub and wheel bearing assembly is used in a four wheel drive vehicle Compare this unit to those shown earlier Note how the drive axle sticks through a stationary spindle An adjustable hub allows the drive axle to be connected and dis connected fr
16. hat the tire is a radial Bias and belted bias tires do not have a second letter The first number 78 is the aspect or 1244 Section 11 Suspension Steering and Brakes P metric tire size P 155 80 R 13 Type tire Section width Height to Tire construction Rim or wheel P passenger in millimeters width ratio radial diameter in car 155 185 195 70 75 80 jas belted inches T temporary A C commercial D diag bias 13 14 15 16 Alpha numeric tire size En Load size Radial design relationship B E F G 78 15 Height to width Rim or wheel ratio diameter in inches 65 70 78 13 14 15 Figure 65 5 Note the two tire size designations A P metric designation B Alpha numeric designation Overall gemeter Normal Section width T eter Overall width Figure 65 6 Points of measurement on a tire These dimen sions are important when ordering new tires or wheels B F Goodrich height to width ratio The last number 15 is the rim diameter in inches The points of measure for a tire are given in Figure 65 6 Aspect Ratio The aspect ratio or height to width ratio in the tire size designation is the most difficult value to understand See Figure 65 7 Note that as the number becomes smaller the tire becomes more squat wider and shorter The aspect ratio is the comparison of the tire s height bead to tread distance and width sidewall to sidewall distance Wid
17. ially on a vehicle s driving wheels The balls allow parts to rotate with a minimum amount of friction and wear Federal Mogul Chapter 65 Tire Wheel and Wheel Bearing Fundamentals The basic parts of a wheel bearing are e Outer race cup or cone pressed into hub steering knuckle or bearing support e Balls or rollers antifriction elements that fit between inner and outer races e Inner race cup or cone that rests on spindle or drive axle shaft There are two basic hub and wheel bearing assembly designs those with tapered roller bearings and those with ball or straight roller bearing assemblies Hub and Wheel Bearing Assembly Tapered Roller Bearings Tapered roller bearings can be used on both driving and non driving The basic parts found in a hub and tapered roller bearing assembly for a vehicle s non driving wheels are illustrated in Figure 65 22 These parts include e Spindle stationary shaft extending outward from the steering knuckle or the suspension system e Wheel bearings tapered roller bearings mounted on the spindle and in the wheel hub e Hub outer housing that holds the brake disc or drum front wheel grease and wheel bearings Outer race Hub Rolar Spindle Grease seal Cage Inner race Cotter pin Dust cap Nut lock Safety washer Hub cavity Grease Figure 65 22 Typical non driving or freewheeling hub and wheel bearing assembly
18. icles used tires equipped with inner tubes Technician B says vehicles always came from the factory equipped with tubeless tires Who is right A A only B B only C Both A and B D Neither A nor B 1255 4 Technician A says an automotive tire s beads are used to stiffen the tire treads Technician B says an automotive tire s beads are used to hold the sidewalls against the wheel rim Who is right A A only B B only C Both A and B D Neither A nor B 5 Technician A says an automotive tire s body plies provide a leakproof membrane for modern tubeless tires Technician B says an automotive tire s liner provides a leakproof membrane for modern tubeless tires Who is right A A only B B only C Both A and B D Neither A nor B 6 Technician A says an automotive tire s belts form the body of the tire Technician B says an automotive tire s belts are sometimes used to strengthen the plies and stiffen the treads Who is right A A only B Bonly C Both A and B D Neither A nor B 7 Technician A says tire rolling resistance is normally reduced by lower inflation pressure Technician B says tire rolling resistance is normally reduced by higher inflation pressure Who is right A A only B B only C Both A and B D Neither A nor B 8 Technician A says belted bias tires provide a smooth ride and good traction Technician B says radial ti
19. ier instal lation and removal of the tire A valve stem snaps into a hole in the wheel of a tubeless tire to allow inflation and deflation Lug nuts hold the wheel and tire assembly on the vehicle e Wheel weights are small lead weights attached to the wheel rim to balance the wheel and tire assembly and prevent vibration Important Terms Tires Pneumatic Tubeless tires Beads Body plies Tread Sidewall Belts Liner Tire rolling resistance Bias ply tire Belted bias tire Radial ply tire Tire markings Tire size P metric Alpha numeric Aspect ratio Maximum load rating Maximum inflation pressure DOT serial number Tread wear Tire traction Tire temperature resistance Tire speed rating Asymmetric tires Directional tires Hydroplaning Spare tire Self sealing Run flat tires Wear bars Tire pressure monitoring system Wheels Drop center wheel Safety rim Valve stem Valve core Lug nuts Lug studs Lug bolts Wheel weights Wheel bearings Hub and wheel bearing assembly Review Questions Chapter 65 Please do not write in this text Place your answers on a separate sheet of paper 1 What are the two basic functions of a tire 2 Car tires are filled with air which means that they are 3 List and explain the six major parts of a tire 4 Tire is a measurement of the amount of friction produced as the tire operates on the road surface 5 Whi
20. ng into the center well in the event of a flat or a blowout DaimlerChrysler Valve T9 Valve core air valve Figure 65 19 A Valve stem snaps into a hole in the wheel B The press fit between the stem and the wheel forms an airtight seal C The valve core is an air valve that screws into the valve stem body The valve cap screws over the end of the stem Toyota 1250 Section 11 Suspension Steering and Brakes and damage It also helps prevent accidental depression of the valve and the resulting loss of air pressure Lug Nuts Studs and Bolts Lug nuts hold the wheel and tire assembly on the vehicle They fasten to special studs The inner face of the lug nut is tapered to help center the wheel on the hub Refer to Figure 65 20A Lug studs are the special studs that accept the lug nuts The studs are pressed through the back of the hub or axle flange See Figure 65 20B Normally the lug nuts and studs have right hand threads turn clockwise to tighten When left hand threads are used the nut or stud will be marked with an L Metric threads will be identified with an M or the word Metric A few cars use lug bolts instead of lug nuts The bolts screw into threaded holes in the hub or axle flange Wheel Weights Wheel weights are small lead weights that are attached to the wheel rim to balance the wheel and tire assembly preventing vibration The weights are used to offset a heavy ar
21. om the hub and wheel assembly for two or four wheel drive operation Toyota Chapter 65 Tire Wheel and Wheel Bearing Fundamentals Steering knuckle bearing support Driving washer Power input from transaxle Drive axle shaft spins inside bearings Wheel ball bearings Figure 65 25 Driving hub and wheel bearing assembly has bearings mounted in a stationary steering knuckle or a bearing support The drive axle shaft fits through the center of the bear ings The hub is splined to axle shaft The ball bearings are lubricated by thick high temperature grease tapered roller bearings These self contained units are not serviceable In most cases they are bolted to the knuckle or support A few are press fit into the knuckle When you need more information on a specific vehicle always refer to the factory service manual It will explain and illustrate the hub and wheel bearing assembly clearly Most designs however will be similar hub screw Outboard yas bearing 1253 Z Note Ball bearings and straight roller bearings are often used in solid rear drive axle assemblies to reduce friction between the axles and the housing Detailed information on rear axle bear ings can be found in Chapter 61 Differential and Rear Drive Axle Fundamentals and Chapter 62 Differential and Rear Drive Axle Diagnosis and Repair Highway History memm Although Michelin introduced the first steel belt
22. peeds The stiff tread area does not give or flex as much on rough roads Tire Markings Tire markings on the sidewall of a tire give informa tion about tire size tire model load carrying ability inflation pressure number of plies speed rating manu facturer etc It is important that you understand these tire markings Refer to Figure 65 4 Tire Size Tire size is given on the sidewall as a letter number sequence There are two common size designations alpha numeric conventional measuring system and P metric metric measuring system The P metric size designation is the newest tire iden tification system It uses metric values and international standards Look at Figure 65 5A The letter P indicates that the tire is designed for use on a passenger car The first number 155 gives sec tion width in millimeters The second number 80 is the aspect ratio height to width ratio The R indicates radial B means belted bias and D means bias ply The last number 13 shows the rim diameter in inches not metric values The alpha numeric alphabetical numerical tire size designation uses letters and numbers to denote tire size in inches and its load carrying capacity in pounds An example is given in Figure 65 5B The first letter G indicates the load and size relationship The higher the letter the larger the size and load carrying ability of the tire G is smaller than H for example The second letter R means t
23. res have a very stable footprint Who is right A A only B B only C Both A and B D Neither A nor B 1256 10 i 12 Section 11 Suspension Steering and Brakes Technician A says a bias ply tire is one of the newest tire designs and is equipped with belts Technician B says a bias ply tire is one of the oldest tire designs and does not use belts Who is right A A only B B only C Both A and B D Neither A nor B Technician A says a radial ply tire s belts are sometimes made of steel Technician B says a radial ply tire s belts are sometimes made of fiberglass Who is right A A only B B only C Both A and B D Neither A nor B Technician A says tire markings on the side wall of a tire give information about tire load carrying ability Technician B says tire markings on the sidewall of a tire provide the maximum recommended inflation pressure Who is right A A only B B only C Both A and B D Neither A nor B Technician A says most automotive wheels are made of steel Technician B says most automo tive wheels are made of aluminum Who is right A A only B B only C Both A and B D Neither A nor B Technician A says wheel bearings in several car models are the tapered roller bearing type Technician B says wheel bearings in certain car models are the ball bearing type Who is right A A only B B only C Both
24. rts of a tire Goodyear Tire Rolling Resistance Tire rolling resistance is a measurement of the amount of friction produced as the tire operates on the road surface A high rolling resistance would increase fuel consumption and wear Typically rolling resistance is reduced by higher inflation pressure proper tire design and lower vehicle weight Tire Construction There are many construction and design variations in tires A different number of plies may be used The plies Bias ply tire Belted bias cords run on bias may run at different angles Also different materials may be utilized Three types of tires found in use today are the bias ply tire belted bias tire and radial tire Bias Ply Tire In a bias ply tire the plies run at an angle from bead to bead The angle is reversed from ply to ply The tread is bonded directly to the top ply See Figure 65 3A A bias ply tire is one of the oldest designs and it does not use belts The position of the plies in a bias ply tire allows the body of the tire to flex easily This tends to improve cushioning action A bias ply tire provides a very smooth ride on rough roads One disadvantage of the bias ply tire is the weakness of the plies and tread which reduces traction at high speeds and increases rolling resistance Belted Bias Tire A belted bias tire is a bias ply tire with belts added to increase tread stiffness The plies and belts normally run at different angle
25. rts to the ones in Figure 65 22 Figure 65 24 shows the front drive hub and wheel bearing assembly for a four wheel drive vehicle Note that it has a driving axle that extends through a stationary spindle A special free wheel or locking hub transfers power from the axle to the hub disc assembly Hub and Wheel Bearing Assembly Ball or Straight Roller Bearings Ball bearings and straight roller bearings are often used at both driving and non driving wheels In most cases the bearings are part of an assembly that includes the inner and outer races The assembly is pressed into the steering knuckle or support Figure 65 25 illustrates the basic parts found in a hub and wheel bearing assembly for the driving wheel of a front wheel drive vehicle These parts include e Outer drive axle stub axle shaft that extends through the bearings and is splined to the hub e Ball bearings antifriction elements that allow the drive axle to turn in the steering knuckle or bearing support 1252 Section 11 Suspension Steering and Brakes Hub and rotor assembly Inner wheel bearing Q Dust or Nut outer Safety hub a i ah ae i Inner Cotter A Spindle face Grease nut seal pin Outer Lug nut Cone and wheel roller assembly Wheel cover bearing Hub stud Figure 65 23 Disassembled view of a nondriving hub and wheel bearing assembly Note the part names and relationships This type of assembly can be used on the
26. s The belts do not run around to the sidewalls they lie under the tread area only Usually two stabilizer belts and two or more plies are used to improve tire performance Look at Figure 65 3B A belted bias tire provides a smooth ride and good traction It also offers some reduction in rolling resistance over a bias ply tire Radial Ply Tire A radial ply tire has plies running straight across from bead to bead with stabilizer belts directly beneath the tread The belts can be made of steel flexten fiber glass or other materials A typical radial tire is illustrated in Figure 65 3C Radial Stabilizer belts Radial cord body plies Chapter 65 Tire Wheel and Wheel Bearing Fundamentals Maximum inflation pressure Temperature index Traction index Tread wear index Maximum load Tire model mer re tiatsaaroa t 93 yas o Tamas z af O 1243 Brand name DOT serial number Mud and snow tire Size Load index s PS Kec WS Speed rating Tread plies Sidewall plies Figure 65 4 Sidewall markings contain information about a tire Study the sidewall markings on this tire A radial tire has a very flexible sidewall and a stiff tread giving it a very stable footprint shape and amount of tread touching road surface This improves safety cornering braking and wear One possible disadvantage of a radial tire is that it may produce a harder or harsher ride at low s
27. special narrow wheel Oldsmobile Tech Tip Most modern spare tires are designed for tem porary use only Refer to the manufacturer s specifications on inflation pressure maximum driving speed and the number of miles that can be driven Most compact spares should not be used at speeds over 50 mph and will last only a few thousand miles Self Sealing Tires Some tires are self sealing seal small punctures These tires have a coating of sealing compound applied to their liners If a nail punctures a self sealing tire air pressure will push the soft compound into the hole to stop air leakage Refer to Figure 65 9 Retreads Retreads are used tires that have had a new tread vul canized applied using heat and pressure to the old car cass or body Retreads also called recaps are seldom used B Nail out om Puncture sealing compound Figure 65 9 Self sealing tire action A Nail punctures the tire B Nail is pulled out C Sealing compound flows into the hole to prevent air from leaking out GMC Run flat construction 0 kgf cm Reinforced inflation sidewall pressure Standard tire Run flat tire Figure 65 10 Compare the construction of a run flat tire to that of a conventional tire Bridgestone on passenger cars However large truck tires are frequently recapped because of the high cost of new truck tires Run Flat Tires Run flat tires have an extremely stiff sidewall
28. ter 65 Tire Wheel and Wheel Bearing Fundamentals Safety Rims A safety rim has small ridges that hold the tire beads on the wheel during a tire blowout instant rupture and air loss or a flat slow leak reduces inflation pressure Small raised lips around the rim keep the tire beads from sliding into the drop center section This improves safety by keeping the tire from coming off the wheel See Figure 65 18 ies Rim width Bolt circle diameter Rear le spacing Figure 65 17 Study the basic dimensions of a wheel Goodyear 1249 Valve Stems and Cores A valve stem is pressed into a hole in the wheel of a tubeless tire to allow inflation and deflation The stem is made of rubber A threaded metal tube is formed in the end of the stem See Figure 65 19 The valve core is a spring loaded air valve that is threaded into the valve stem Figure 65 19 The valve core allows air to be added to the tire when an air chuck tool for filling tire with air is placed over the valve stem When the air chuck is removed from the valve stem the spring pushes the valve closed to prevent air leakage To remove air from the tire push the center of the valve core inward The valve will open allowing air to escape A valve stem cap screws over the threaded valve stem to protect the air valve and stem threads from dirt moisture Safety ridges Well Wheel Figure 65 18 Safety ridges prevent the tire from droppi
29. th Height Hei ight is 70 lis 65 z of wi width 70 series tire 65 series tire aspect ratio 70 aspect ratio 65 Figure 65 7 The aspect ratio is the height to width ratio of tire Note that a 65 series tire is wider and shorter than a 70 series tire A 70 series tire for example has an aspect ratio of 70 the height of the tire is 70 percent of the width A 60 series tire would be short and fat A 78 tire would be narrow and tall Maximum Load Rating The maximum load rating of a tire indicates the amount of weight the tire can carry at the recommended inflation pressure The maximum load value 1500 pounds for example is printed on the sidewall With P metric tire designations the load rating is simply given in kilograms and pounds The alpha numeric load rating is indicated by a letter Most alpha numeric size tires are load range B They are restricted to the load specified at 32 psi 220 kPa Where a greater load carrying ability is needed load range C or D tires are used Chapter 65 Tire Wheel and Wheel Bearing Fundamentals Maximum Inflation Pressure The maximum inflation pressure is the highest air pressure that should be pumped into the tire Many tires have a maximum recommended inflation pressure of 32 psi 220 kPa However tires with higher load ranges can hold higher pressures and carry more weight Tread Plies The tire sidewall also includes information on the number of
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