Episode 160 – Understeer vs Oversteer

Welcome to the Executive Protection, and Secure Transportation Podcast brought to you by the International Security Driver Association. The topic for this week’s episode is understanding understeer and oversteer.

Understeer and Oversteer are terms used to explain vehicle characteristics, and they are important signals transmitted to you by the vehicle, it is how the vehicle communicates to you. It is the vehicle’s way of telling you what you should do next. In a nutshell, understeer and oversteer are the interrelationships of the front and rear ends of the car.

To get a clear understanding of understeer and oversteer, a basic discussion of the laws of physics is required. When you turn the steering wheel, there is energy pushing on the Center of Gravity (CG) of your vehicle. The amount of energy (which can be measured in G’s or pounds) is determined by how much you move the steering wheel and how fast you’re traveling. The more speed and the more steering, the more energy pushing on the vehicle. Remember from high school “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 understeer. Please note, in these demonstrations the vehicles do not use electronic stability control.

Understeer (If you are a NASCAR fan this is called “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. Using 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 understeering condition turning the steering wheel more won’t work and will aggravate the scenario. To fix it, reduce speed, and reduce the amount of the steering wheel is turned. You can correct understeer by reducing throttle until the front tires regain adhesion.

Oversteer (NASCAR fans 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 make things worse. In our example, the rear tires can push back with only 1000 lbs. and the fronts push back with 1600 lbs.

Just to repeat – You can’t learn to correct understeer and oversteer by reading a book or article.

To fix oversteer reduce speed and turn the steering wheel in the opposite direction of the skid.

By far one of the most difficult situations to correct something called power oversteer. An example of power oversteer; you’re in pursuit or for whatever reason driving fast around a corner – as you as, and the back of the vehicle starts to swing out. The back of the vehicle is swinging out because you have too much gas and the back tires are losing 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 steer, either to drive around a corner or in an emergency maneuver 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. Correct trailing-throttle oversteer by smoothly increasing the throttle (to transfer weight to the rear tires) and apply steering to counter the rotation.

So what is dangerous understeer or oversteer? Although understeer and oversteer can both cause loss of control, many cars are designed to understeer, it is believed by car designers that understeer is easier to control. In fact, almost all cars you drive have understeer built into them.

From a driving standpoint what is hard to do and considered by many to be a dangerous characteristic, 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 ( understeer) entering the corner and loose (oversteer) coming out. This condition is one of the very few that will cause a NASCAR driver to slow down.

That will bring us to the end of another episode of the EPST podcast, I hope you will join us next week for another episode. Show notes for this episode are available at the SecurityDriver.Com website. If haven’t done so already, make sure to subscribe to the podcast in your favorite podcast app and if you’ve been listening for a while, let us know what you think by leaving us a review on Apple of Google.

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