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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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For the past 28 years, I have been a member of the Washington State Driver Training Planning Committee. During this time, our agency built a strong working relationship with the Washington State Patrol. Together, we designed an advanced training curriculum on vehicle dynamics for Washington driver trainers to teach in an effort to prepare our state’s 12,000 school bus drivers for unexpected moments out on the open road.

Given that we transport precious cargo, knowing the dynamics of your vehicle is essential. Understanding vehicle dynamics will allow you to maintain optimum control, even in the most unexpected driving conditions and during inclement weather, because you will understand the effects when maneuvering in and out of traffic on roadways, and you will understand how road conditions impact the operation of your bus.

Here, I’ll explain some factors and their role in vehicle dynamics.

1. Pre-trip inspection
If you are expecting a vehicle to be able to respond and react to your immediate needs, you must first perform a thorough pre-trip inspection.  The vehicle needs to meet all state and federal criteria to operate on a public roadway.

2. Tires
The tires are often the most neglected area of a vehicle, but they are one of the most vital components for you to maintain control of the vehicle. Proper tread depth and inflation are key factors.

3. Centrifugal force or inertia
This is the force that keeps an object traveling in a straight line. As a vehicle attempts to negotiate a curve in a road, centrifugal force or inertia tries to push the vehicle to the outside of the curve, keeping it moving in a straight line. Imagine a ball on a string as you swing it around in a circle and then let it go — it will continue going straight.

4. Friction
Friction is resistance to slipping. Non-moving friction is called static friction, and moving friction is dynamic or coefficient friction. Our job is to keep as much friction between the tires and the surface of the road as possible. Without friction, a vehicle would be impossible to control.

5. Contact patch (footprint of bus)
The contact patch is where the tires and road surface actually meet. If you were to hold your hand up, the contact patch would not be much larger than your hand while the bus is at a resting position. Multiply this by six for a school bus with six tires. Your contact patch will vary in size according to the inflation of the tires; it is best to use the recommended air pressure for the tires you have.

  • Both under- and overinflated tires will decrease the contact patch. Underinflated tires will have a tendency to invert cup the tire and reduce the contact patch with the roadway. Overinflated tires will peak the tire, meaning it is bulging in the center. Once again, this will decrease the contact patch with the road surface.
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