The phrase Under and Over Steer are used often in training to explain vehicle characteristics. Understeer and oversteer is a condition that describes what happens to a vehicle when you move the controls, specifically the steering wheel.

When you turn the steering wheel there is energy pushing on the Center of Gravity (CG) of your vehicle, and it makes no difference who you are, what you are driving, or where you are driving it, the laws of physics dictate that when you move the steering wheel, you create a force acting on the cg of the vehicle. The amount of energy (it can be measured in G's or in pounds) is determined by how much you move the steering wheel and how fast you're traveling. It's pretty simple, the more speed and the more steering the more energy pushing on the vehicle. Remember from high school science "for every action there is an opposite and equal reaction". So if there is a force pushing on the CG of your vehicle, there has to be an equal and opposite force pushing back - that force pushing back is created by the friction your tires make with the road.

If you drove around a corner or made an emergency maneuver that created 3200 lbs pushing on the CG of your vehicle - in the perfect world your tires would be pushing back 1600 lbs front and rear. This would be called neutral steering, and it is a characteristic seldom found in vehicles.

But what happens most often is that the vehicle will either oversteer or understeer. What follows below is a BASIC explanation of under over steer.

Understeer (the NASCAR guys call this "push") - in a turn, or emergency maneuver understeer is the condition where the front tires lose adhesion while the rear tires remain in contact with the pavement. The car tends to travel straight ahead, even though you are turning the wheel. In our example the front tires can only push back with 1000 lbs and the back tires push back with 1600 lbs.

You can't learn to correct under and over steer by reading a book or article etc. But I'll give it a shot, keeping in mind that this is as basic an explanation as you can get.

In an under steering condition turning the steering wheel more won't work and will aggravate the scenario. To fix it reduce speed and/or reduce the amount the steering wheel is turned. You can correct understeer by reducing throttle until the front tires regain adhesion.

Oversteer (NASCAR guys call this "loose") -- In a turn, or emergency maneuver oversteer is the condition where your rear tires lose adhesion while your front tires remain in contact with the pavement. The back end of your car tends to slide out. Turning the steering wheel more will makes things worse.

Let me repeat - You can't learn to correct under and over steer by reading a book or article.

To fix oversteer reduce speed and turn the steering wheel in the opposite direction of the skid. In our example the rear tires can push back with only 1000 lbs and the fronts push back with 1600 lbs.

Correcting oversteer can be tricky and requires training and practice. Then there is something called power oversteer.

An example of power oversteer; you're in pursuit or for what ever reason driving fast around a corner - as you exit the corner you apply gas, and the back of the vehicle starts to swing out. The back of the vehicle is swinging out because you have applied too much gas and the back tires are loosing adhesion - to correct the problem you either have to steer less and give it less gas.

Also there is another form of oversteer that is called trailing throttle oversteer, which means that as you turn and take your foot off the gas the back of the car swings out. Trailing throttle oversteer is due to the back tires doing funky things when you transfer weight from the rear to the front. (very common in armored vehicles). Correct trailing-throttle oversteer by smoothly increasing the throttle (to transfer weight to the rear tires) and apply steering to counter the rotation.

What separates da mens from da boys, is a vehicle that goes quickly from understeer to oversteer, or vice versa. You hear it often when watching a NASCAR event; they will say that the car was tight entering the corner and loose coming out. This is something you got to learn to control.

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