Vehicle Balance

In this section we will learn about the following:

• The reason and need for vehicle balance.
• How vehicle speed impacts vehicle balance.
• How performing vehicle operation and control tasks to accelerate, decelerate, steer (straight, right, left), move forward, back, and stop manages vehicle balance.
• How performing vehicle operation and control tasks may result in an imbalance situation.
• How the position of the seat, driver's posture, seating position, and safety belt usage affect the ability to manage vehicle balance.
• How the vehicle imbalance in traction loss, roll, pitch, and yaw situations change the vehicle operating space, line of sight, path of travel, lane placement, right-of-way, following interval, vehicle speed, and communication and formulate plans to compensate.
• Formulating plans to avoid or compensate for variances in roadway grade and shoulder conditions that impact vehicle maneuvers and vehicle balance.
• How vehicle balance varies from vehicle to vehicle and formulate plans to compensate for variances including utilizing the vehicle owner's manual as a resource.

Vehicle Balance

Vehicle balance is the distribution of vehicle weight on the tires, as they meet the ground. The amount of “tire” touching the surface of the ground has a bearing on a vehicle’s handling and balance. A vehicle’s balance is affected by tire pressure and suspension geometry. The optimum balance is only attained when a vehicle is at a stop, at which point the amount of “tire patch” touching the surface of the ground is at its greatest.

Transfer of Weight and Balance Occurs:

• When a vehicle is in motion
• During Acceleration, Deceleration or Cornering (or any combination of)

This transfer will cause changes to both the vehicle balance and weight on the tire patches.

When the vehicle is traveling at a constant speed, stopped or there is no acceleration or deceleration; the suspension is set on center and the steering and traction conditions are considered to be in balance.

Vehicle Balance

Steering or speed adjustments to compensate for vehicle suspension changes and weight transfers are often necessary to maintain vehicle balance. The weight of a vehicle can be concentrated on one of four points, on the chassis, depending on the changes in speed.

• The front of the chassis (over the front tire patches)
• The rear of the chassis (over the rear tire patches)
• The center of the chassis (distributed equally over the front and rear tire patches)
• On one or two points on the chassis based on steering or surface changes;
• to the right of center (right two tire patches), or
• to the left of center (left two tire patches).

Vehicle Balance

Rate of acceleration, brake application pressure, steering input, surface traction and road conditions affect vehicle balance by creating shifts in weight and also affect a driver's ability to maintain control of the vehicle.

• Balance is maintained through precise steering movements, smooth and progressive acceleration and controlled brake application
• Proper seating position (with safety belts engaged) allows the feet, legs, arms and hands to maintain a stable position and maximize vehicle movement (kinesthetic) feedback
• In a vehicle with an automatic transmission, the right foot operates the accelerator and service brake pedals. The heel of the right foot remains in contact with the floorboard and pivots between both pedals. The left foot should be placed on the “dead pedal” which is an area vehicle manufacturers have designated for the left foot to balance the driver

Seating Position

Proper seating position plays a critical part in a driver’s ability to safely operate a vehicle and its controls. It also plays an important role in establishing vehicle balance and bettering the driver's ability to see the roadway.

Drivers should sit in a comfortable, upright position squarely behind the steering wheel with safety belts fastened. Adjust seat height so that the top of the steering wheel is in line with the top of the shoulders. The top of the wheel should never be more than one inch higher than the top of the shoulders. In vehicles without power seats and/or adjustable steering columns or tilt steering wheels, some drivers may need to use a pillow or cushion to obtain the best seating position.

Proper distance from the steering wheel can be determined by extending the arm straight forward and adjusting the position of the seat, forward or backward, until the top of the steering wheel is in line with the wrist joint.

Vehicle Balance (Roll, Pitch, and Yaw)

Roll

Vehicle moves side-to-side on its long axis. (Imagine an airplane when one wing goes up and the other goes down.)

Pitch

Vehicle moves forward or backward. (For example, when accelerating, the nose of the vehicle goes up and the back of the vehicle goes down and when braking, the nose of the vehicle goes down and the back of the vehicle goes up.)

Yaw

Vehicle movement left or right. (For example, the front of the vehicle moves left and the rear of the vehicle moves right - or vice versa.)

Changing Vehicle Balance

From Rear to Front (Pitch)

Erratic or sudden steering, accelerating or braking affects vehicle balance from rear to front. When brakes are applied, weight or center of mass is transferred to the front of the vehicle. When braking hard, there is a noticeable drop of the hood and rise of the rear of the vehicle and occupants feel forward movement of their bodies. The most efficient way to slow or stop your vehicle is to brake while traveling in a straight line. This allows the braking force to have an evenly distributed effect on all four wheels.

The ability to apply the correct brake pedal pressure is learned through experience and practice. However, each vehicle has a different “feel” with which a driver must become familiar. Apply too little pressure and the vehicle will not stop at the desired spot or within the distance available. Apply too much pressure and the brakes may lock up, and traction and directional control may be lost.

Changing Vehicle Balance

From Left to Right (Yaw)

Yaw is caused by:

• Sudden braking
• Sudden or excessive acceleration
• Sudden or excessive steering
• Road tilted to right
• Traction loss to right rear

Responding to Changing Vehicle Balance

Drivers must be in sync with the “feel” of their vehicle to minimize risks from sudden maneuvers and changes in vehicle balance. Sudden steering or improper combinations of braking and steering can cause traction loss, roll, pitch, and yaw situations. Whether you are traveling at a high or low speed, this imbalance and load transfer can create a dangerous situation that will change the vehicle's operating space, line of sight, path of travel, lane placement, right-of-way, following interval, vehicle speed, and communication.

To compensate, use proper steering techniques to help you maintain control of the vehicle. Always use both hands to steer a vehicle moving forward or turning. You may use one hand to steer, only when backing (left hand at the 12 o’clock position for maximum control).

Steering Movements

• Hand-to-Hand
• Limited Evasive Steering
• Hand-over-Hand
• One-Hand Steering (typically only used when backing)

Responding to Changing Vehicle Balance

Variances in roadway grade and shoulder conditions impact the control a driver has during vehicle maneuvers and affects vehicle balance. A driver must apply a systematic pattern of visual searching to effectively manage varying and dangerous road conditions.

Searching Pattern

• 20-30 seconds ahead
• 12-15 seconds ahead
• 4-6 seconds ahead
• Search to the sides
• Search to the sides
• Search blind spots

Search the road for:

• Roadway Features
• Changes in Driving Environments
• Signs, Signals and Road Markings
• Other Motorized Vehicles
• Non-motorized Traffic
• Vulnerable Roadway Users

Responding to Changing Vehicle Balance

Patience, experience and maturity play a large role in a driver’s ability to safely operate a motor vehicle. Experience allows a driver to become more adept at recognizing traffic patterns and potential hazards, allowing them to anticipate and adjust efficiently and safely.

Vehicles vary in size and handling capabilities, so drivers must be able to adjust to both the driving environment and their vehicle.