21February

Tips From a Pro: Understeer and Oversteer

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By: Thomas Merrill

 

All of the rules we obey and the roads we drive on are designed to keep us at roughly thirty percent of our car’s maximum grip potential. This, of course, is designed to keep us safe. However it also presents an opportunity for mistakes to be made, and bad habits formed, without the driver ever knowing it. This is also why we always hear the phrase “all of the sudden” when the average driver describes a loss of control. The car never does anything “all of the sudden,” barring any mechanical failure. Understanding the basics of exceeding the tire’s grip can help us stay in control.

The first type of grip loss is called understeer. Understeer, also known as “push” or “tight,” is a loss of grip at the front end of the car. Simply put, the car wants to continue strait as the front wheels turn. The most common form of understeer is caused by accelerating too soon in a corner, lifting the weight distribution, and grip, off of the front tires. However turning the wheel too fast, and too far, can also cause understeer. The steering wheel is most intuitive control in the car. On the road, below the limit of the car, more wheel equals more turning. This is not so at speed. The tire wants to go strait, so the more we turn it, the less it actually wants to grip.

The most dangerous form of understeer is caused by over-loading the front tires. Consider the tire’s contact patch. Within that grip restriction, the tire will grip for braking, accelerating, and turning, each at 100% capability… but only one at a time. When entering a corner too quickly, it is common to brake, and turn, at 100%, in an effort to stay on the road. This never ends well, and is always the cause of head-on crashes into things like trees and telephone poles.

In any case, the solution to understeer is to stop, or release, the last control input. In the cases of braking too much or turning too much, fixing an understeer can be very counter-intuitive. The secret to overcoming this is proper vision technique. Look only where the car should go, not where it shouldn’t go, and the solution will become much more clear.

The second type of grip loss is called oversteer. Also called “free” or “loose,” oversteer is exactly what it sounds like, the car is steering too much. Fundamentally, the rear end of the car has lost grip, and begins to overtake the front. Those of us trained to drive in the U.S. know to turn the wheel in the direction of the “skid.” This, however, is only the first of a three-step process. Turning in the direction of the skid is called a “correction.” Pointing the front tires helps them stay in front of the rear… but only as long as the rear tires are sliding. After a successful correction, the small period of time before the rear tires regain their grip is called the “pause.” This period of time is influenced by the speed of the vehicle, the type of tire, the accuracy of the correction, and every other dynamic variable. The trick to predicting the pause length is, again, vision. Looking to where the car should be, instead of where it is sliding to, will give every driver an intuitive feel for the pause. Finally, once those rear tires regain their grip, the car will go where the front tires are pointed. If they are not pointed where the car should go, the car will quickly slide in the opposite direction. This is where the term “over-correction” comes in, and it doesn’t really describe the problem. The driver didn’t over-correct, the driver under-recovered. The recovery is the last step in the process, and is simply the act of straitening the wheel out and pointing the front tires where the car should go. This correct, pause, recover technique, or CPR, will always fix an oversteer if used correctly.

However whether the problem is understeer or oversteer, the solution is always difficult if the driver is not looking for the best possible scenario. Forward, accurate vision will make all these techniques intuitive, and seamless.

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