Modern Automotive Technology

1. Modern Automotive Technology by Russell Krick PublisherThe Goodheart-Willcox Co., Inc.Tinley Park, Illinois PowerPoint for

2. Chapter 65 Tire, Wheel, and Wheel Bearing Fundamentals

3. Contents • Tires • Wheels • Valve stems and cores • Lug nuts, studs, and bolts • Wheel weights • Hub and wheel bearing assemblies

4. Tires • Tires perform two basic functions: • act as a soft cushion between the road and the metal wheel • provide adequate traction (friction) with the road surface

5. Tire Types • Pneumatic • filled with air • internal air pressure pushes out on the inside of the tire to support the vehicle • Tubeless tire • does not use an inner tube • tire and wheel form an airtight unit • Tube-type tire • uses an inner tube to hold air pressure

6. Tubeless Tire

7. Parts of a Tire

8. Tire Rolling Resistance • Measurement of the amount of friction produced as the tire operates on the road surface • High rolling resistance increases fuel consumption and wear • Rolling resistance is reduced by higher inflation pressure, tire design, and a lighter vehicle

9. Tire Construction • There are many design variations: • different numbers of plies may be used • plies may run at different angles • different materials may be used • Three types of tires used on automobiles: • bias ply • belted bias tire • radial tire

10. Bias Ply Tire • Plies run on an angle from bead to bead • Angle is reversed from ply to ply • Does not use belts • Body of the tire flexes easily • Provides a smooth ride • Plies and tread are weakest • reduces traction at high speeds • increases rolling resistance

11. Bias Ply Tire

12. Belted Bias Tire • Bias tire with belts added to increase tread stiffness • Belts lie under the tread area only • Two stabilizer belts and two or more plies improve tire performance • provides a smooth ride and good traction • reduces rolling resistance

13. Belted Bias Tire

14. Radial Ply Tire • Plies run straight across from bead to bead • Stabilizer belts lie beneath the tread • Belts can be made of steel, flexten, fiberglass, or other materials

15. Radial Ply Tire • Uses a very flexible sidewall with a stiff tread • provides a very stiff footprint • improves safety, cornering, braking, and wear • may produce a harsher ride at low speeds

16. Radial Ply Tire

17. Tire Sidewall Markings

18. Tire Size Alpha-Numeric–Uses letters and numbers to denote tire size in inches and its load-carrying capacity in pounds

19. Tire Size P-Metric–Uses metric values and international standards

20. Points of Measurement

21. Aspect Ratio Height-to-width ratio of a tire. Comparison of a tire’s height and width

22. Maximum Load Rating • Amount of weight the tire can carry at the recommended inflation pressure • Printed on the sidewall • P-metric: • given in kilograms and pounds • Alpha-numeric: • indicated by a letter such as B, C, or D

23. Maximum Inflation Pressure • Highest air pressure that should be pumped into the tire • Many tires have a maximum recommended pressure of 32 to 40 psi (220 to 275 kPa)

24. Tread Plies • Number of plies and ply rating: • 2-ply • 2-ply with a 4-ply rating • 4-ply • Greater number of plies usually indicates a greater load-carrying capacity

25. DOT Serial Number • Identifies the manufacturer, plant, location, construction, and date of manufacture • Stamped into the sidewall • Department of Transportation rating means the tire has passed prescribed safety tests

26. Tire Grades • Tread wear • given as a number, 100 to 500 • higher number is more resistant to wear • Tire traction • given as an A, B, or C • “A” rating has the most traction • Tire temperature resistance • given as an A, B, or C • “A” rating resists temperature buildup best

27. Speed Rating • Maximum allowable sustained road speed a tire can safely withstand without failure • Ratings range from B to Z • “B” rating 31mph or 50 km/h • “Z” rating 149 mph or 238 km/h

28. Wear Bars When too much tread has worn away, solid rubber bars will show up across the tread

29. Compact Spare Tire This is a high pressure spare, requiring60 psi (415 kPa)

30. Self-Sealing Tires • Coating of sealing compound is applied to the liner • If a nail punctures the tire, air pressure will push the soft compound into the hole to stop air leakage

31. Self-Sealing Tire Action A. Nail punctures tire B. Nail is pulled out C. Sealing compound flows into the hole

32. Retreads • Used tires that have had a new tread vulcanized to the old carcass, or body • Large truck tires are often recapped because of the high cost of new truck tires

33. Run-Flat Tires • Use extremely stiff sidewall construction • Still usable with a loss of air pressure • Tire will still retain most of its shape because the sidewall is strong enough to support vehicle weight

34. Run-Flat Tires

35. Tire Inflation Monitoring System • Often used with run-flat tires • Pressure sensors are mounted on each wheel • If tire pressure is not correct, the wheel sensor produces a radio signal • Signal is received by a module that turns on a dash warning light

36. Pressure Sensor

37. System Operation

38. Wheels • Designed to support the tire while withstanding loads from acceleration, braking, and cornering • Made of steel, aluminum, or magnesium • Lightest weight is desirable to reduce “unsprung” weight, improving handling

39. Wheel Assembly

40. Mag Wheels Aluminum or magnesium wheelsare often called “mags”

41. Drop-Center Wheel • Allows for easier installation and removal of the tire • Center of the wheel is smaller in diameter than the rim • When installing a tire, it can fall into the recess, then, the other side of the tire bead can be forced over the rim

42. Drop-Center Wheel Note the smaller diameter in thecenter of the rim

43. Dimensions of a Wheel

44. Safety Rims Small ridges on the rim hold the tire on the wheel during a tire blowout or flat

45. Valve Stems and Cores • Valve stem • pressed into a hole in the wheel of a tubeless tire to allow inflation and deflation • Valve core • spring-loaded air valve that is threaded into the valve stem • Valve cap • protects the air valve and stem threads from dirt, moisture, and damage

46. Valve Stem Assembly Valve stem snaps into the holein the wheel Press fit forms an airtight seal Valve core screws into the valve stem body

47. Lug Nuts, Studs, and Bolts • Lug nuts • hold the wheel and tire assembly on the vehicle • Lug studs • special studs that accept the lug nuts • Lug bolts • used instead of nuts • screw into threaded holes in the hub or axle flange

48. Lug Nut and Stud Stud is pressed into the hub oraxle flange If metric or left-hand threads are used, markings will normally be given

49. Wheel Weights • Small lead weights • Attached to the wheel rim to balance the wheel-and-tire assembly • Used to offset a heavy area of the wheel and tire

50. Hub and Wheel Bearing Assemblies • Allow the wheel to turn freely around the spindle, in the steering knuckle, or in the bearing support • Most wheel bearings are tapered roller bearings or ball bearing