The Dynamics of a Vehicle Emergency

Anytime the steering wheel is moved while the car is in motion, a lateral or sideways force is created. This force is pushing in the opposite direction the car is turning. This force is an expression of inertia, or, as stated in Newton’s First Law of Motion, a body at rest tends to remain at rest unless an outside force is applied to it, and a body in motion tends to remain in motion, again, unless an outside force, such as the turn of a steering wheel, is applied.

The term G’s is a measurement of the force acting on the car. A tenth of a G can make the difference between having or not having an accident.

As an example – If the path of a Ford Police Interceptor Sedan, that weighs approximately 4500 lbs is altered in a way that produces a single G (1G), that G force is equivalent to 4,500 lbs. of force pushing the car away from its desired path.

The equation for computing this force is simple: The amount of force pushing on the car is equal to the G’s times the weight of the vehicle. If we turned our 4,500 lb. car in such a way that .7G was created, then we would have created 3,150 lbs. of force or 4,500 X .7g’s = 3,150 lbs. If the car weighed 4,000 lbs. and was turned the same way, the equation would read 4,000 lbs. X .7 g’s = 2,800 lbs., and so forth.

The lateral G-forces created in a turn are based upon both the vehicle’s weight and how much the steering wheel is moved or the degree, or sharpness, of the turn.

According to a test conducted by one of the car magazines, the Cornering Power of a Ford Police Interceptor is .83 G’s. If there were .8 G’s pushing on the Center of Gravity (CG), there would be 3600 pounds pushing on the CG.

This chart shows a breakdown of common G’s and pounds on the center of gravity

The question that is important for trainers is how much weight can the driver apply to the CG of the Ford before bad things happen?

Consider that there have been a number of studies done that indicate that the average driver uses (handles) only 40% of the vehicle’s capability. If an average driver were maneuvering through a slalom course, they would start to have problems when they apply 40% of the vehicle weight to the vehicle’s CG. In the case of the Ford Interceptor that would be 1800 Lbs pushing on the CG of the vehicle.

 Future articles and webinars will go deeper into these numbers. We will cover how to compute maximum speed through various exercises before things get exciting.