Publisher The Goodheart-Willcox Co., Inc. Tinley Park, Illinois

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

2. Chapter 74 Wheel Alignment

3. Contents • Wheel alignment principles • Caster • Camber • Toe • Steering axis inclination • Setback • Toe-out on turns (turning radius) (Continued)

4. Contents • Tracking • Prealignment inspection • Adjusting wheel alignment • Wheel alignment tools and equipment • Alignment machines • Road test after alignment

5. Wheel Alignment Principles The main purpose of wheel alignment is to make sure the tires roll without scuffing, slipping, or dragging under alloperating conditions

6. Alignment Angles • Six fundamental angles are needed for proper wheel alignment: • caster • camber • toe • steering axis inclination • toe-out on turns (turning radius) • tracking (thrust line)

7. Caster • Forward or rearward tilt of the steering axis (steering knuckle) when viewed from the side of the vehicle • Controls the tire’s load distribution in relation to an imaginary centerline drawn through the spindle support • Caster does not affect tire wear

8. Caster A shopping cart caster wheel illustratesnegative caster

9. Caster A bicycle wheel represents positive caster

10. Purposes of Caster • Aid directional control • Cause the wheels to return to the straight-ahead position • Offset road crown pull (steering wheel pull caused by the hump in the center of the road)

11. Positive Caster • Tilts the top of the steering knuckle toward the rear of the vehicle • Helps keep the wheels traveling in a straight line • When the wheels are turned, it lifts the vehicle • The vehicle’s weight tends to push the wheels back to the straight-ahead position

12. Positive Caster More common on vehicles with power steering

13. Negative Caster • Tilts the top of the steering knuckle toward the front of the vehicle • The wheels will be easier to turn • The wheels will tend to swivel and follow imperfections in the road

14. Negative Caster May be used on vehicles with manual steering, to ease steering effort

15. Caster Measurement Measured in degrees, from true vertical

16. Caster and Road Crown Effect Road crown is the normal slope toward the outer edge of the road surface

17. Caster and Road Crown Effect • Road crown causes the weight of the vehicle to pull the vehicle away from the center of the road • Caster is commonly used to offset the effect of road crown • The right front wheel may be set with slightly more positive caster than the left • the vehicle pulls toward the side with the more negative caster

18. Camber • Inward or outward tilt of the wheel and tire assembly when viewed from the front of the vehicle • Controls whether the tire tread touches the road surface evenly • Affects tire wear

19. Purposes of Camber • To prevent tire wear on the outer or inner tread • To load the larger inner wheel bearing • To aid steering by placing the vehicle’s weight on the inner end of the spindle

20. Positive and Negative Camber • Positive camber • the tops of the wheels tilt outward when viewed from the front • most manufacturers specify a positive setting of about 1/4º to 1/2º • Negative camber • the tops of the wheels tilt inward when viewed from the front

21. Positive and Negative Camber

22. Camber Measurement Measured in degrees, from true vertical

23. Toe • Difference in distance between the front and rear of the left- and right-hand wheels • Measured in inches or millimeters • Controls whether the wheels roll in the direction of travel • Affects tire wear

24. Toe Toe-in: wheels are closer at the front than at the rear Toe-out:wheels are farther apart at the front than at the rear

25. Rear-Wheel-Drive Toe Settings • Rolling resistance and steering system play tend to cause toe-out when driving • Toe-in compensates for these factors • By adjusting the front wheels for a slight toe-in, the wheels and tires roll straight ahead when driving • Typical setting: • 1/16"–1/4" (1.6 mm–6 mm)

26. Front-Wheel-Drive Toe Settings • The front wheels are pushed forward by engine torque, causing the wheels and tires to toe in • To compensate for this action, front-wheel-drive vehicles normally have the front wheels adjusted for a slight toe-out • Typical setting: • 1/16" (1.6 mm)

27. Steering Axis Inclination • The angle, away from the vertical, formed by the inward tilt of the steering axis (ball joints, king pin, or MacPherson strut tube) • Aids directional stability by helping the steering wheel return to the straight-ahead position • Does not affect tire wear

28. Steering Axis Inclination If the angle is incorrect, partreplacement is needed

29. Setback • One front wheel is set farther back from the front of the vehicle than the other front wheel • with positive setback, the right wheel is farther back than the left wheel • with negative setback, the left wheel is farther back than the right wheel • Excessive setback will cause pull

30. Setback • Manufacturing tolerances generally allow a small amount of setback • Excessive setback is usually the result of collision damage

31. Toe-Out on Turns (Turning Radius) • Amount the front wheels toe-out when turning corners • As the vehicle corners, the inside tire must travel in a smaller radius circle than the outside tire • The inside wheel turns sharper than the outside wheel

32. Toe-Out on Turns

33. Toe-Out on Turns • Eliminates tire scrubbing and squealing by keeping the tires rolling in the right direction during turns • Not an adjustable angle • If the angle is incorrect, it indicates bent or damaged steering parts

34. Tracking • Position or direction of the two front wheels in relation to the two rear wheels • With the proper tracking, the rear tires follow in the tracks of the front tires • With improper tracking, the rear tires do not follow the tracks of the front tires • increased tire wear, lower fuel economy, and handling problems can result

35. Tracking

36. Prealignment Inspection • Before attempting wheel alignment, make sure all steering-related and suspension-related parts are in good condition • It is impossible to properly align the wheels on a vehicle with worn or damaged parts

37. Prealignment Inspection Points • Check for the following: • loose wheel bearings • wheel or tire runout • worn tires • tires of different sizes and types • incorrect tire inflation • worn steering or suspension components • incorrect curb height and weight • incorrect cradle alignment

38. Reading Tire Wear

39. Cradle Alignment • The cradle is the strong metal structure bolted to the frame rails on the body • holds the lower control arms, steering rack, and engine in alignment in the body • Loosening and moving the cradle can alter alignment • Alignment holes may be provided in the cradle and body to assure proper alignment

40. Adjusting Wheel Alignment Caster, camber, and toe are the three commonly adjustable wheelalignment angles

41. Caster andCamber Adjustment

42. Caster and Camber Adjustment

43. Toe Adjustment Changing the tie-rod length on arack-and-pinion unit

44. Toe Adjustment Changing the tie-rod length ona linkage-type steering system

45. Centering Steering Wheel

46. Adjusting Rear Wheel Alignment • Some vehicles have provisions for rear wheel alignment • Rear wheel alignment problems can occur due to component wear or damage • Procedures for rear wheel adjustment vary

47. Adjusting Rear Wheel Alignment On this axle, shim placement changes alignment angles

48. Wheel Alignment Tools and Equipment • Various equipment and special tools are needed • The most basic equipment includes the turning radius gauge, the caster-camber gauge, and the tram gauge • Alignment racks integrate the functions of all these gauges into one machine

49. Wheel Alignment Tools

50. Wheel Alignment Tools A. Steering wheel lock B. Brake pedal depressor