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August 01, 2013  |   Comments (0)   |   Post a comment

10 factors that affect vehicle dynamics

Understanding vehicle dynamics will help the driver maintain optimum control of the bus, which is essential to maintaining student safety. Here, factors ranging from tires and centrifugal force to weight shift and acceleration are addressed.

by Marcia Hahn


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8. Braking

When braking, the weight shifts to the front of the vehicle, providing increased traction to the front tires. The footprint at the front is now larger, creating a better steering situation.

9. Curve negotiation techniques

Plan on reducing your speed to your maximum negotiable speed before entering a curve. The best rule of thumb is to use the threshold braking method: be firm but smooth on the brakes at first and more aggressive on the brakes up to the start of the curve, but never too abrupt. Do not stab the brakes, as this may cause wheel lockup. Get off the brakes as you start your turn. This is also called straight-line braking. This technique provides more steering ability to your front tires.

10. Apex
The apex is the halfway point of the curve. Set yourself up “high” prior to entering a curve. You would want to be in the lane as far to the outside as possible. This would be on the opposite side of the curve’s turn. If it is a left curve, follow the fog line; for a right curve, follow the center line, but never go over the center line.  

Smoothly steer the vehicle toward the apex, maintaining a constant speed — do not brake during the lateral weight change (turning in the curve). Continue through the curve until the roadway begins to straighten out. You start high in the curve, drift low and drift back high again to the furthest portion of the lane. Apply power at or just past the apex, accelerating to rebalance the footprint of the tires.

Summary
Identifying how vehicle dynamics affect operating the vehicle is essential to student safety. The primary objective is to maintain a positive contact patch between the vehicle’s tires and the surface of the road.

Marcia Hahn is a school bus driver trainer instructor for the state of Washington. She is also transportation director at Wenatchee (Wash.) School District #246.

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