Vehicle Balance, Traction Loss, Roadway and Vehicle Technology Driver Education

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 Vehicle Movement on Crowned or Banked Roadway –Can create dramatic changes to vehicle balance due to suspension and weight shifts Controlling Vehicle Balance

Steering Wheel BalanceSteering Wheel Balance –Smaller steering wheel design –Rack and pinion steering control Precise Steering, Braking, and Accelerator InputPrecise Steering, Braking, and Accelerator Input –Less steering movement needed in modern vehicles –Need smooth acceleration/deceleration –Squeeze brakes for balanced stops Changes in Steering Ratios, 1980's to DateChanges in Steering Ratios, 1980's to Date -Steering input has been significantly reduced Maintaining Vehicle Balance

Changing Vehicle Load from Side to Side (Roll) Steering Wheel Movements Brake Application and Steering Combinations Slope of pavement Controlling Vehicle Balance Seating Driver position/balance and safety belt/pedal use

Releasing the accelerator Controlled braking (Squeeze on) Threshold braking Trail braking (Squeeze off) Changing Vehicle Load from Front to Rear (Pitch) Light accelerator pressure Releasing the brake Progressive accelerator pressure Thrust accelerator pressure Changing Vehicle Load from Rear to Front (Pitch) Vehicle Direction / Speed Requirements

Weight Shifts Change Vehicle Balanced DROPS Front LIFTS Rear Accelerating, braking, or steering shifts the vehicle’s weight from tire to tire and affects vehicle balance and control. Weight Shifts

Sudden braking and steering Sudden or excessive acceleration and steering Sudden or excessive steering Road tilted to right Traction loss to right rear may cause yaw motion Sudden braking and steering Sudden or excessive acceleration and steering Sudden or excessive steering Road tilted to left Traction loss to left rear may cause yaw motion Changing Vehicle Load from Right to Left (Roll) Changing Vehicle Balance from Left to Right (Roll) Vehicle Direction / Speed Requirements

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

Vehicle Control Vehicle Direction / Speed Requirements Steering Wheel Control  Hand position on steering wheel Holding top or upper half of wheel (excessive steering and air bag injury risk) Hands located on lower half of wheel (relaxed, balanced control)  Steering techniques Hand-to-hand steering (Push/Pull/Slide) Hand-over-hand steering (top third of wheel) Evasive steering (ABS wheel limitation) One-hand steering -To reach controls -At top when backing straight -At bottom when backing a trailer

Covering the brake - placing the right foot over the brake but not applying break pressure Controlled braking (squeeze on) – braking with sufficient pressure to slow the vehicle while maintaining vehicle balance Threshold breaking – 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

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 drive

Types of Traction Three types of traction influence the control/or movement of a motor vehicle. 1.Static: stationary car with brakes set, greatest resistance to movement. 2.Rolling (dynamic): more traction than with a sliding wheel Driver must keep wheels rolling and not sliding: don’t lock brakes 3.Sliding: loss of traction

Front Wheel Loss of Traction Termed “Understeer” 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 Corrections Direct vision to path of travel Ease off steering Re-establish rolling traction

Rear Wheel Loss of Traction Termed “Oversteer” 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 Corrections 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

Vehicle Technology ABS: Anti-lock brakes which are designed to allow steering and simultaneous braking without losing vehicle balance. Anti-lock brakes do not necessarily shorten stopping distance on dry pavement, but generally shorten stopping distances on wet surfaces where traction loss can be a serious problem. Traction Control Devices: Designed to activate brake sensors which do not allow the wheels to spin. The process is basically the reverse of anti- lock brakes. Allows acceleration input without loss of vehicle balance.

Automotive Technology Suspension Control: Adjusts 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. Electric Stabilization 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.