VEHICLE DYNAMICS BASICS

Tony Scotti

Vehicle dynamics, two words you tend to hear often, unfortunately most people don’t quite understand what the words mean and how it affects their day to day driving. As an example I recently reviewed a solicitation for driver training from a military entity. They asked the bidders to include a “vehicle dynamics exercises”. Well driving to the shopping mall, parking your car, parallel parking are all exercises in vehicle dynamics.

Vehicle Dynamics is the application of the laws of physics to a vehicle in motion. That vehicle can be a fighter jet, train, or a horse draw cart. In our case it is a vehicle with four rubber tires or two or 18 rubber tires as I have done in some training. The basic principals are the same no matter how many tires are attached to the vehicles. Hence when driving down the highway, around corners, or trying to drive out of a potentially dangerous scenario, the vehicle driver combination must operate within the laws of physics and specifically within Sir Isaac Newton’s three laws of motion.

If driving is a big part of your life personally or professionally having an understanding of vehicle dynamics will make for a more enjoyable driving experience. For driver trainers, at any level of instruction, in depth knowledge of vehicle dynamics is a must. It transforms an average instructor into a professional instructor. Yet most people shy away from using the laws of motion to better understand their vehicle and better yet their level of driving skill. For most people their only exposure to the laws of physics is what they were taught in high school. With all due respect to high schools the subject is mired in books and seems to have no practical value. In our training program we find that even those who are math challenged, once the theory is explained in English versus engineer talk, and they turn a classroom discussion into hands on practical scenarios, it is amazing how all that math actually makes sense.

All driving scenarios, no matter how simple or complex, are an exercise in the laws of physics. Makes no difference if it's high risk, low risk, or what government, military, and police agencies think when it comes to the laws of physics the driver and in the security world your adversary must live within them - it is what it is.

The Vehicle Dynamics Series
This is the first in a series of articles on vehicle dynamics and how it applies to training – security and every day driving. The articles will appear on SecurityDriver.Com and in my blog. Most articles written on vehicle dynamics are produced by engineers who speak a language know only to other engineers – the language is mathematics. A typical 20 page Society of Automotive Engineer (SAE) research paper can be summed up in about a page when it is converted to English. Their language is equations, some of them complicated, to express their findings. It is the natural way of conducting research. I have a degree in Engineering, read about two to three SAE papers a month, and will make every attempt to write the articles in a clear and understandable manner. If I don’t - let me know.

One of the issues we will cover extensively, and a point that is getting a lot of attention from NHTSA and DOT, is that driving performance is a measurable skill. This is a concept that is still hard for most people to grasp, even for those that conduct driver training programs. At one time these skills were hard to measure, and required some knowledge of engineering. But with today’s technology measuring driving performance is easily attainable.

Newton’s 3rd Law of Motion
Remember from high school “for every action there is an opposite and equal reaction”. So if there is a force pushing on the Center of Gravity (CG) of the vehicle, there has to be an equal and opposite force pushing back – that force pushing back is created by the friction the tires make with the road, makes no difference if there is 2 – 4 or 18 tries. When the driver turns the steering wheel to maneuver around a corners or an emergency scenario, there is energy pushing on the CG of the vehicle. The amount of energy is determined by how much the student moves the steering wheel and how fast they are traveling. The more speed and the more steering the more energy pushing on the vehicle, if they apply too much speed or too much steering the result is under or over steer. Refer to this article for more in depth information.

The 3rd Law and the Comfort Zone/Red Zone
We all have a combination of speed and steering that we are comfortable with. But in an emergency the driver will be required to go past their Comfort Zone, way past it into the Red Zone. The driver has to be trained for that occasion, and during training has to drive into the Red Zone. In fact the objective of training is to raise the drivers comfort zone. In the Red Zone, the driver will notice a big difference in how the car reacts to their inputs. The steering wheel and gas pedal become very sensitive. When a driver gets to the Red Zone small changes in steering or speed create big changes in the way the vehicle responds. How much the driver can turn the steering wheel depends on how much gas the driver has applied. Simply put the steering wheel and the gas pedal are connected. To make it more interesting the vehicle can be in the Red Zone but not the driver. A future article will go in depth about life in the Red Zone.

All data indicates that going from the Comfort Zone to the Red Zone, which means the difference between success and failure is measured in tenths of a seconds, tenths of inches on the steering wheel, and/or 2 MPH. You cannot determine this change in speed, timing, or steering by looking at the vehicle or by sitting in the passenger seat looking at the speedometer. In fact seating in the passenger seat to measure driver performance is absurd. Driver performance needs to be monitored at all times and corrections need to be made based on objective data. There is nothing the driver does with the vehicle that cannot be measured by a computer or by taking empirical data. This also will be the subject of a future article.

Any questions or comments contact me at tonyscotti@securitydriver.com