1. Vehicle Balance, Traction Loss, Roadway & Vehicle Technology (DE3, DE13,
Driver Education

2. Vehicle Balance A matter of balance
Vehicle suspension balance refers to the distribution of the weight of the vehicle on the chassis.
A transfer of weight occurs whenever you:
accelerate
brake
turn
or perform some combination
of these actions.

3. Weight Distribution
Weight can be shifted from the center to the front, rear, left or right tires.
When the vehicle is stopped, or traveling straight at a constant speed, its suspension and traction are stabilized.

4. Maintaining Vehicle Balance
Vehicle balance is the distribution of the weight of the vehicle on the tires
Optimum balance is reached when the vehicle is not moving or is moving in a straight direction at a constant speed
As soon as the vehicle accelerates, brakes, or turns, the balance is changed and the weight transfer changes the size of the tire patches

5. Controlling Vehicle Balance
Vehicle Balance (Roll, Pitch, and Yaw)
Roll: vehicle’s weight shifts from side to side
Pitch: vehicle’s weight shifts forward or backward
Yaw: vehicle’s rear tire weight shifts to one side
Note: These weight transfers occur when the amount of weight or force pulling on each tire changes
Optimum balance is achieved at rest with no movement
Suspension and tire pressure also affect vehicle balance

6. Roll, Pitch and Yaw Pitch Roll Yaw
Pitch, Roll, and Yaw are the three axes running through a vehicle’s center of gravity
Roll
Yaw
Pitch

7. Roll
Vehicle’s weight shifts to the tires located on one side of the vehicle
Which direction is this driver steering to cause this weight shift? What causes a vehicle roll over?

8. Changing Vehicle Suspension - Pitch
Front to Rear (Pitch)
When a vehicle accelerates, its weight shifts to the rear.
Rear to Front (Pitch)
When the brakes are applied, the vehicle’s weight, or center of mass, is transferred to the front.

9. Vehicle Pitch Vehicle’s weight shifts backward or forward
Forward Pitch
Changing Vehicle Load from Rear to Front
Backward Pitch
Changing Vehicle Load from Front to Rear

10. Vehicle Yaw
Yaw = Fishtailing Vehicle’s rear tires lose traction and weight shifts to one side while opposite rear wheel moves toward front of vehicle
No Yaw
Yaw

11. Changes in Speed Affects Balance and Control
Pushing or releasing the accelerator pedal is the primary method to adjust the speed of a vehicle
Changes in speed causes weight shifts to front or rear tires
Increases in speed with steering adjustments causes significant shifts in the vehicle’s weight

12. Braking Affects Balance Control
How does braking affect balance and control in a front or rear-wheel drive vehicle?

13. Effects of Hard Braking & Steering
Applying hard braking causes weight to shift sharply to the front tires
If the weight shift exceeds available traction, the tires will skid and steering control is lost (under steer)
Load Decreasing
Load Increasing

14. Vehicle Suspension Helps to smooth out weight transfers
Helps keep all four wheels on the ground
Helps keep the vehicle level

15. Steering and Balance
Accelerating, braking, or steering shifts the vehicle’s weight from tire to tire and affects vehicle balance and control
Describe the driver’s action and how is it affecting this vehicle’s balance?

16. Cornering Cornering Inertia Actual Path Intended Path
When cornering, tires tend to flex.
Intended Path
RIM
Apex
Tires turning left
If the tires are underinflated, the contact with the rim may be lost. AIR LOSS WILL OCCUR.
Excessive tire flexion increases tire heat and may result in a blowout.
Cornering

17. Braking
Covering the brake - placing the right foot over the brake but not applying brake pressure
Controlled braking (squeeze on) – braking with sufficient pressure to slow the vehicle while maintaining vehicle balance
Threshold braking – braking to a point just short of wheel lockup
Trail Braking (squeeze off) – used to maintain speed and balance. This technique is often used at the end of controlled or threshold braking.

18. Braking Techniques Smooth braking technique:
Is a trait of a skilled driver
Saves wear and tear on the brake system and tires

19. Methods to Reduce Speed
Release the Accelerator
Most frequently used method to slow vehicle speed
Gradually reduce pedal pressure to avoid abrupt changes in speed

20. Methods to Reduce Speed
Controlled Braking - When releasing the accelerator is not enough
Check the rear view mirror
Release accelerator and apply smooth, steady pressure on the brake pedal
For a smooth STOP, gently ease off the brake a few seconds before stopping to reduce the vehicle’s weight shift so the car does not pitch forward then backward during the final phase of stopping

21. Threshold Braking in an Emergency
Slows the vehicle as quickly as possible without locking brakes or losing traction
Release accelerator while checking traffic behind
Exert forceful pressure on brake pedal and you will feel the vehicle weight shift forward
If you feel the wheels begin to slide, ease the pressure on brake pedal so the tires can begin rotating again

22. Trail Braking Used for Sharp Turns
Occurs at the transition point where you slightly reduce pressure on the brake pedal to allow the vehicle to begin to regain speed before applying the accelerator

23. Trail Braking 1. Use controlled braking prior to reaching the curve
2. Begin easing off brake, and trail brake with very light pressure until halfway through the turn,
3. Accelerate out of the turn

24. Vehicle Suspension and Traction
Single-vehicle crashes
Improper steering or braking or both can upset a vehicle’s balance, which can lead to a loss in traction and an unintended path of travel.
More than 50 percent of occupant fatalities occur as a result of single- vehicle crashes.
Almost without exception single-vehicle crashes involve improper steering or braking or a combination of the two.

25. Road Surface and Traction
Traction: Traction is the adhesion, friction or grip between the tires and the road surface.
Question: How does traction vary and what can affect it?

26. Traction
Traction or adhesion is the grip between the tires and the road surface which allows a vehicle to start, stop and/or change direction
Causes of traction loss (skidding) can be divided into three categories
Condition of the road
The vehicle
Actions of the driver

27. Types of Traction
Three types of traction influence the control/or movement of a motor vehicle.
Static: stationary car with brakes set, greatest resistance to movement.
Rolling (dynamic): more traction than with a sliding wheel
Driver must keep wheels rolling and not sliding: don’t lock brakes
Sliding: loss of traction

28. Causes of Traction Loss
Driver Actions that may cause TRACTION LOSS:
Sudden steering actions on a slippery surface, or abrupt or sudden changes in vehicle speed
Panic stop or applying the brakes too hard on a hill, curve or slippery surface
Suddenly engaging the clutch on a slippery surface
Most driver-induced skids are caused by:
excessive speed
coupled with excessive steering input
or improper braking when turning
Loss of traction also occurs with these driver’s actions at normal speeds on ice/snow or on roadways covered by sand, gravel, or water

29. Traction Loss Considerations
When the BRAKES are applied TOO HARD or QUICKLY
Weight Moves to the Front of the Car Causing
a noticeable drop of the hood
a noticeable rise of the rear deck
forward movement of driver and passengers

30. Traction Loss Considerations
When ACCELERATION is applied TOO HARD or QUICKLY
Weight Moves to the Rear of the Car Causing
a noticeable rise of the hood
a noticeable drop of the rear deck
rearward movement of driver and passengers

31. Traction Loss Considerations
When Steering is Applied Too Hard or Quickly
Weight Moves to the Opposite Side of the Car
Weight Movement Causes:
a noticeable drop and tilt of the hood
a noticeable rise and tilt of the rear deck
driver and passenger movement towards the car’s corner

32. Front Wheel Loss of Traction
Termed “Understeer”
Corrections
Vehicle moving straight ahead in spite if steering input
May first be identified visually
Tires tend to roll under
Rear wheels tend to push front straight ahead
Direct vision to path of travel
Ease off steering
Re-establish rolling traction

33. Types of Skids

34. Rear Wheel Loss of Traction
Termed “Oversteer”
Corrections
Rear wheels try to assume front position
Generated by slick surface, speed, braking or sudden steering input
Identified visually as front of vehicle moves left or right of travel path without steering input in that direction
Direct vision to path of travel
Ease of brake or accelerator
Steer back toward path of travel
Direct vision to travel lane not road shoulder
Light progressive acceleration may be needed to return rear tire traction

35. Automotive Technology
Anti-lock brake systems are designed to allow steering and simultaneous braking without losing vehicle balance.
Traction control systems are designed to activate brake sensors, which do not allow the wheels to spin. The device allows acceleration input without loss of vehicle balance.

36. Automotive Technology
Suspension control systems adjust vehicle balance at struts or shock absorbers through adjustment of fluid or air pressure when too much weight is suddenly transferred to a given shock or strut.
Electronic Stability Program (ESP) compares where a driver is steering the vehicle with where the vehicle is actually going. When ESP senses a disparity between the two, it selectively applies any one of the vehicle’s brakes to reduce the discrepancy and help the driver retain control and stability.
In Case of Oversteering
When ESP detects oversteer, it applies the outside front brake.
In Case of Understeering
When ESP detects understeer, it applies the inside rear brake to help the vehicle rotate faster.

37. Anti-Lock Braking System (ABS)
ABS allows maximum stopping force without locking up the brakes (skidding) If standard brakes are applied too hard, the wheels "lock" or skid, and you lose steering control.

38. Anti-Lock Braking System (cont)
If steering control is lost, the vehicle skids in a straight line wherever it is going
ABS is an anti-lock/anti-skid brake system that allows the driver to steer during hard braking

39. Anti-Lock Braking System (cont.)
The ABS warning will come on when there is a problem with either the ABS brake system, normal brake system, or the brake fluid is low in the master cylinder or the ABS brake system
To find out if a vehicle is equipped with ABS, turn on the ignition and check the instrument panel for the ABS indicator light

40. 2 Types of ABS 4-wheel ABS: Rear-wheel ABS:
Generally found on passenger cars;
Designed to maintain steering ability in emergency braking situations
Rear-wheel ABS:
Found exclusively on light trucks;
Designed to prevent the vehicle from skidding laterally
2 Types of ABS

41. Practice Activating ABS
In a parking lot, go mph and execute an emergency stop to engage ABS
Keep your foot firmly on the brake even when you feel the brake pulsate and/or hear noise
This computerized pumping action can pump the brakes up to 15 times per second

42. Do maintain firm & continuous pressure on the brake while steering to enable 4-wheel ABS to work properly
Do allow enough distance to stop:
Follow 4 or more seconds behind vehicles if conditions are good;
Follow 6 or more seconds if conditions are adverse
ABS Do’s

43. Do practice with ABS in empty parking lots to become familiar with the pedal pulsations
Do consult the owner’s manual for additional instructions
ABS Do’s

44. ABS Don’ts Don’t drive an ABS-equipped vehicle more aggressively
Don’t pump the brakes:
Pumping the brake turns the ABS system on & off
Don’t be alarmed by the noises & pedal pulsations
Don’t forget to steer
ABS Don’ts

45. Myths about ABS Don’t use ABS brakes on a slippery surface
There are fewer fatal crashes for cars equipped with ABS
False, some drivers panic and/or release the brake when it pulses
Don’t use ABS brakes on a slippery surface
False, ABS shortens stopping distance and improves control on a slippery roads

46. Anti-Lock Brake System With ABS, Do Not…
Drive More Aggressively
Pump the Brakes
Steer Too Much
Be Alarmed by ABS Noise or Vibration