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

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.

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.

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

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

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

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?

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.

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

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

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

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

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

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

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?

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

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.

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

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

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

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

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

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

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.

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?

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

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

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

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

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

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

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

Types of Skids

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

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.

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.

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.

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

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  

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

Practice Activating ABS In a parking lot, go 20-25 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

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

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

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

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

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