This article will discuss the Vehicle’s Center of Gravity (CG).
First, some basic definitions:
The Center of Gravity. The Center of Gravity (CG) is the point on the vehicle where all the weight is balanced. It is measured from the ground to a point in the vehicle’s height and width. All forces acting on a vehicle act through the CG.
The height of the center of gravity. The height of the CG relative to the wheelbase determines weight transfer between the front and rear. CG height to track width determines the weight transfer from side to side.
Weight above the center of gravity. In an armored vehicle, the weight above the CG is an important vehicle characteristic. It determines the vehicle’s tendency to roll over and is a significant factor in the vehicle’s emergency maneuvering capability.
Additional weight on the tires affects the contact patch. All vehicles are supported by a cushion of air contained in four flexible rubber tires. Each of these four small patches of rubber is known as the “contact patch.” These are the only points of contact between the armored vehicle and the road. It is these four patches that create the traction that makes the vehicle – go – stop, and turn – that send the feedback back to the driver, and it is these four patches the driver has to manage. Consider them to be a source of information needed to control the vehicle. The contact patch is sensitive to weight – all modifications made by the armorer affect the contact patch. The next newsletter will cover armored vehicles and tires. An article:
http://vehicledynamics.com/the-tire-contact-patch/
The Problem
In an emergency maneuver – either accident avoidance or vehicle violence – the driver will be required to apply 80 to 100 % of the vehicle’s weight pushing on the vehicle’s CG. The concerns:
- The CG height – The higher the CG, the more weight will be transferred to the vehicle’s tire contact patch.
- The weight above the center of gravity. The majority of the vehicle’s weight comes from the windshield. The heavier the windshield and the greater the distance from the CG to the windshield, the more weight is transferred to the contact patch.
Questions on CG Height
Has the armorer computed the CG height? Although this may seem complicated, there are some simple methods that can be used to determine CG.
Questions on Weight Transfer
Have the spring and shock absorbers been modified to compensate for the additional weight and weight transfer? Not just add stiffer springs and more shocks – has the manufacturer computed/measured the weight transfer and thoughtfully compensated for the additional weight transfer?
Questions – Braking
An increase in weight also decreases brake life. The energy the brakes must absorb and dissipate is a function of the vehicle’s weight and changes in speed. What has the manufacturer done to compensate for the additional energy the brakes must absorb?
Ask the armored vehicle manufacturer if the vehicle has been tested to the PAS 301 Standards. PAS 301 is a standard that describes test methods that may be completed on a civilian armored vehicle (CAV) to assess its automotive characteristics for payload, acceleration, maximum speed, through gear acceleration, handling, braking, and run-flat.
ANSI supplies and a short 9-page outline of the standard.
This is a YouTube video outlining the test procedure.
Remember that armor changes the vehicle’s characteristics, and you have to accept those changes for the protection that armor provides.
Additional Resources
If you have an interest in Security Driving, Secure Transportation, or Executive Protection, the International Security Driver Association (ISDA) offers several resources worth considering.
One option is to sign up for the ISDA’s LinkedIn Newsletter, “Security Driver Journal,” a twice-monthly educational email publication that contains articles written specifically for the Security Driver/Secure Transportation community. This resource provides continuing education and benchmark research to help improve your skillset and advance your business.
Another resource is the ISDA’s YouTube channel, which features playlists containing videos covering topics such as Case Studies of Vehicle Attacks, Security Driving, Armored Vehicles, and the Business of Security.
Those interested in connecting with other professionals in the industry can also follow the ISDA’s LinkedIn page, which provides educational content on various topics related to Security Driving and Secure Transportation, including Armored Vehicles, Secure Transportation Business Metrics and Data, Surveillance Detection, The Change in Executive Vehicles, and Case Studies, Including Lessons Learned.
Lastly, visitors can check out the ISDA Store for hats, t-shirts, decals, and other merchandise related to the organization and secure transportation.