Instructors’ ‘27 T Roadster

1. Instructors’ ‘27 T Roadster

2. Class Participation Rules • Please Participate • Agree, disagree, comment, share your opinion and experiences, ask questions etc. but just don’t sit there. • Remember this class is a lot more fun when I’m not the only person talking.

3. Seminar Itinerary • Break(s) as needed through out the class. • How many of you have not had lunch? • 150 slides in the alignment theory portion of the class. • Class time today 12 to 6 pm. Tomorrow class time is 1 pm to 7 pm. • Shop time will be the later part of the class today and tomorrow. • Remember please participate.

4. Class presentation prepared by:

5. Understanding The AnglesAutomotive Wheel Geometry A Technician’s Guide to Wheel Alignment

6. Quick, name 15 alignment related angles/references that you will deal with on every wheel alignment! 1. Camber (front) 2. Caster (front) Is there ever rear caster? 3. Toe (front) 4. Camber (rear) 5. Toe (rear) 6. Thrust

7. 15 alignment related angles/references cont. 7. GCL (Geometric Center Line) 8. VCL (Vehicle Center Line) 9. Scrub Radius 10. RSR (Road Surface Resistance of the tire) 11. Camber Roll 12. Slip Angle 13. Over Steer, Under Steer, Neutral Steer 14. Dominant Force 15. Dynamic loaded angle changes (toe compliance)

8. Now name 15 more alignment related angles/references What do you mean that you can’t think of another 15 alignment related angles/references that affect the tire wear and handling of a vehicle? Doesn’t everyone know about the 2000 model year spindle offset change GM made on some of their FWD cars and what it does for handling? Do you know about increased spindle height? Why Ford is using it on their new SUV’s and why it’s almost a 100% positive design feature with virtually no negative features. 16. 17. 18. 19. 20. 21. 22…..

9. Ride Height

10. Ride Height • Ride Height is not listed in your student book as a separate section. • How ride height affects various alignment adjustments and setting is covered under the various individual sections. i.e.. Camber, Caster, Scrub. • The following Ride Height information is presented to give everyone the same foundation about Ride Height problems.

11. Ride Height • Check Spec Manual for Specs and Measurement Points

12. Ride Height Measurements Facts • Just measuring for a side-to-side or front-to-rear comparison is not measuring ride height. • Even within a car family, similar body styles shared between different name plates, the ride height specs are not always the same. • Sometimes measuring ride height correctly is a real pain.

13. Ride Height Related Problems • Q. Which alignment angle is affected most by a rear to front ride height problem? (The rear of the vehicle is lower than the front.) • A. Caster, the suspensions upper pivot points move rearward. • Q. How much caster change, and which way, + or -, do you get when the trunk is loaded and the rear of the car angles 3 degrees downward? • A. A 3 degree positive caster change.

14. Ride Height Related Problems • Q. Why does a car handle so poorly when the trunk is overloaded, i.e.. 8 bags of cement mix, if caster moves positive when the rear of the car drops (supposedly you get more stability with increased caster)? • A. Because of the weight transfer to the rear there is now less RSR (road surface resistance) between the front tires and the road.

15. Ride Height Related Problems • Q. If you have a vehicle with one corner lower than the other, sagged or broken spring, what alignment related angles or directional influences come into play? • A. Camber change, caster change (with rear spring problem), understeer/oversteer depending on which spring has problem and at least five other angles.

16. Vehicle Handling Characteristics • Oversteer (Loose) • Understeer (Pushing) • Neutral Steer

17. Oversteer • The rear tires drift out when the vehicle is driven in a circle, when the front wheels are turned from straight ahead. • The vehicle will have a tendency to turn tighter than steering wheel input. • When power is put to the wheels the car will turn sharper. • Usually referred to as being “loose”.

18. Understeer • Front tire drift causes the vehicle to refuse to turn as sharply as the wheels are pointed. • With the steering wheel held in place and the throttle constant a vehicle will make an ever increasing larger circle (pushing) outward. • Most FWD (Front Wheel Drive) vehicles have built in Understeer tendencies.

19. Neutral Steer • Front and rear tire drift is the same. • The vehicle goes where it is pointed. • Would create a driving safety hazard for most people. Especially those who use a cell phone and don’t pay attention to where they are steering. • Isn’t used on the average vehicle sold in the U.S. • Neutral steer doesn’t idiot proof a vehicle.

20. Camber

21. Camber Definition • Viewed from the front, camber is the inward or outward tilt of a tire and wheel assembly from true vertical. • Tilted outward = Positive Camber • Tilted inward = Negative Camber

22. Camber Example RF LF -1 degree camber +1 ½ degree camber This vehicle has a 2 ½ camber split (spread) and should have a severe pull to the right.

23. Camber Facts • All other things being equal a vehicle will pull/drift toward the side with the most positive camber. • Camber is always assumed to be positive. If you are stating or writing about negative camber you must say negative or use the minus sign. • If no sign minus sign (-) is present the reading/specification is positive.

24. Camber Facts • A tire with positive camber is attempting to roll around the apex of the cone created by positive camber. • A tire with positive camber will wear on the outside edge. • A tire with negative camber will wear on the inside edge.

25. Camber Facts • This RF tire would attempt to roll right. If the left side did not have an equal amount of offsetting camber the vehicle would go right. Apex of the cone RF tire Direction of travel Road Surface

26. Proving Camber Facts • Take a Styrofoam coffee cup and lay it on its side (empty it first). • Visually extend a line down the side to the table surface. This is the apex of the cone. • Gently blow on the side of the cup and note that is is pivoting around the point where the line contacts the table top.

27. Camber Pull Demonstration This tire/wheel will pull to the right as it attempts to rotate around the apex of the cone established by the tilt of the tire/wheel assembly. Vehicles direction of travel. Imagine that this is the right front tire with positive camber (outward tilt of the tire).

28. Camber Pull Demonstration Right Front Cup Started Here X Apex of the cone If the left front tire does not have an opposing force the vehicle will go to the right. Remember that the spindle and knuckle are attached to the tire/wheel so whatever force is present at the tire will be transferred to the vehicle.

29. Camber Facts • Because the entire tire must rotate at the same RPM, speed, and because the one side has a smaller diameter than the other scuffing will occur, on the outside edge. RF tire Smaller diameter Direction of travel Road Surface

30. Camber Facts • If a tire/wheel is angled inward, toward the engine, camber is negative. • If a tire/wheel is angled outward, away from the engine, camber is positive. • Many late model (1998 & later) vehicles have set static camber negative. • There are over 23 million vehicles on the road that have camber specified negative. Why?

31. Camber Effect & Radial Tires • Radial ply tires are not affected by camber as much as bias-belted or bias-ply tires are. • On the rear of a FWD vehicle it usually takes more than 1 degree of camber before any tire wear is present provided toe is set correctly. • On the rear of a vehicle if toe is out of adjustments even slightly any amount of camber over .5 degree will usually amplify the misadjusted toe condition.

32. Camber Effect & Radial Tires • Because camber doesn’t greatly affect handling on a vehicle equipped with radial ply tires whenever possible it is best to compensate for road crown with caster. • It is best to compensate for road crown with caster even if you must install an aftermarket adjustment kit to do so.

33. Camber Roll

34. Spindle Height- Spindle Spread • Definition: • The mid-point of distance between the pivot points of the spindle (the ball joint tapered holes at the end of the spindle). • Purpose: • Greater spindle height/spread minimizes camber changes during vehicle dive and chassis roll.

35. Spindle Height is the mid-point between the upper and lower ball joints. This mid-point is shown by the RED arrow on the picture at the right. Upper ball joint Lower ball joint

36. The greater the spindle height/spread/length the less side force is placed on ball joints during jounce, rebound, vehicle dive and chassis roll. Refer to the TOTAL ALIGNMENT AUTOMOTIVE WHEEL GEOMETRY “UNDERSTANDING THE ANGLES” A Technicians Guide To “Wheel Alignment book for further information.

37. Caster

38. Caster Definition Viewed from the side caster is the forward or rearward tilt of a line drawn through the steering axis compared to true vertical. Zero Caster NegativeCaster Positive Caster

39. Caster Definition & Facts • Remember that the steering axis is defined as a line drawn through the suspension pivot points (ball joints) compared to true vertical. • Note that the true vertical line is always measured straight up from the center of the tire contact patch NegativeCaster X Positive Caster

40. Caster Reaction Positive Caster = Directional stability. Excessive positive caster means hard steering but the power steering easily overcomes the effect. Negative Caster = Less stability especially at highway speed. Excessive negative caster gives the feeling of instability, wandering and light steering. Zero Caster NegativeCaster Positive Caster

41. Provided there is no other dominant force a vehicle will pull to the side having the least amount of positive Caster. That is the same as the most negative caster. Caster is not a direct tire wearing angle until you turn the wheels from a straight ahead position then the camber roll, caused by positive caster, can cause tire wear. Caster Reaction Zero Caster NegativeCaster Positive Caster

42. 0 Degree Caster Load Point Location With 0 Caster the point of load is directly in line with the true vertical line. RF RF Upper BJ RF Lower BJ RF Direction of travel shown in red. Direction of travel

43. Positive Caster Load Point Location With Positive Caster the point of load is in front of the true vertical line. True Vertical Line Upper BJ RF Lower BJ Direction of travel Direction of travel

44. Positive Caster Effect • Increased Positive Caster = • Increased Vehicle Stability. • Increased Steering Effort. (Easily overcome by the vehicles Power Steering). • Increased steering wheel returnability after a turn. • Increased road shock from bumps. • Increase in the effect of bump steer problems.

45. Positive Caster Effect Without Positive Caster Angel The Caster Line is through the center of the upper and lower ball joints. The actual center of the spindle has been moved back from the caster line. This gives a Caster effect without a high Caster angle.

46. ASE Test Question • Caster causes tire wear: • A: Directly • B: Indirectly • C. Not at all • D. Depends on the suspension design. • E. This is really a lousy ASE test question.

47. Caster causes tire wear: • When the wheels of a vehicle with positive caster are turned from a straight ahead position caster causes the camber to change (roll). • The more positive caster you have the more camber roll (change) you get. • The more you turn the wheels the more camber roll (change) you get.

48. 4 x 4 Trucks & Camber Roll The larger the diameter and the wider the tire the more camber wear problems you will have because of camber roll. Visualize a 4x4 truck with “mudder” type of tires and a caster setting of 5 ½ degrees (positive) being constantly driven in town making tight turns. You can now understand why the tire will chunk out and show irregular thread block wear. The only solution is to lower the caster and this is only a partial solution. Rotation also helps but nothing is a cure.

49. Plus Size Tires & Camber Roll The larger the diameter and the lower the profile (aspect ratio) the more tire wear problems you will have because of camber roll. Plused sized tires with lower aspect ratios have shorter sidewalls than higher profile tires. This means that the springing effect of the tires sidewall is demised. Any force put into the tire will have a higher degree of reaction on the tire face. In other words the tires edge will be loaded quicker and with more force because the sidewall of the tire does not flex as much.

50. Bump Steer