Understeer and oversteer

Understeer and oversteer are terms that are used liberally in the automotive community and by enthusiasts. You come across them everywhere, from blogs to banter. If you are not completely sure what these words really mean and are too embarrassed to ask, then this is for you. In this issue we will expand on the topic of understeer and oversteer.

Understeer and oversteer is a deviation from the normal. Most car manufacturers engineer their cars to handle neutrally and predictably when going around a corner. Many people may spend their entire driving life without a car once understeering or oversteering. It is only when a car is pushed harder, outside it’s  comfort zone that the laws and dynamics of physics will catch up to make the car understeer or oversteer.

Good tyres are a must to prevent your car from understeering or oversteering.
Good tyres are a must to prevent your car from understeering or oversteering.

UNDERSTEER
Let’s begin by answering, “what is an understeer?” Understeering is when the car continues to plough straight, even after you turn the steering wheel. To an observer it would seems like the driver has applied insufficient steering lock – or understeered.

Usually its front-wheel cars that tend to understeer, while rear-wheel drive cars oversteer. To understand why it’s the front-wheel cars that characteristically understeer, take a look at the front wheels. The front wheels must not only propel the car forward but also handle braking and steering. Forcing the front tyres to handle all the load together can overwhelm them and give up, sending the car straight rather than around the corner.

One of the most common causes for understeering is braking into a corner. When you stomp down on the middle pedal, the maximum braking effort falls on the front wheel as the car’s weight is transferred forward. The tyre is using most of its grip to scrub speed – and if at this moment you make a steering input, the tyre will just not have enough grip to make that turn. It will just continue in a straight line. If this happens, reduce your brake pressure to free up more grip for steering and hopefully you will make your turn. If you want to avoid understeering, finish your braking while you are in a straight line and then make your turn.

Road conditions, too, can cause a car to oversteer or understeer.
Road conditions, too, can cause a car to oversteer or understeer.

While braking into a corner can cause you to understeer, so can accelerating hard through a corner. Remember, the tyres have a limited amount of grip. When you are accelerating into a turn, the grip is distributed between accelerating and steering. The more you accelerate, the less grip there is to steer. Accelerate too hard, and there will be no grip left to steer. To correct this kind of understeer, all you need to do is reduce steering lock and ease off the throttle to free up more grip. There is also the added benefit of forward weight transfer – that again, means more grip in the front. Do note, we said ‘ease off the throttle’, not completely lift off the throttle. When you do that, the weight of the car is suddenly transferred to the front axle, making the rear end very light, potentially causing the car to spin on its axis. This is called a lift-off oversteer – but we will tackle the subject of oversteer a little later.

At times understeering can be caused by low traction conditions on the road. Oil, black ice and gravel can cause the car to understeer – especially if you encounter them around a corner.

So what can you do to avoid understeering? First rule of thumb is to be as smooth as you can be. Secondly, don’t enter into a corner too fast and also, don’t brake in a corner.

OVERSTEER
Now let’s talk about the oversteer. Oversteering is similar to understeering but occurs when the rear tyres reach the limit of grip in a corner, before the front ones. This causes the back to come outward and the car ends up rotating on its axis. If you manage to perform sustained, controlled oversteering this is known as drifting. It’s a tendency in powerful, rear-wheel-drive cars for their tail-lights to overtake the headlights during cornering. If you are a fan of the three merry men in Grand Tour, you rarely see them test a car without some sort of oversteering. Yes, oversteering looks cool as the car slithers around, billowing smoke from its tyres but what looks good on a racetrack or airstrip is not as good on a public road – since this usually foreshadows a big accident.

An oversteer can happen for a variety of reasons. The most common is that you have come into a corner with too much throttle, which means the rear tyres spin and begin to slide. Another means of oversteering is lifting off the throttle, which we touched upon, earlier. Basically, when you lift off the gas the weight of the car is suddenly thrown forward, which makes the rear end very light – which, in turn, reduces traction on the rear wheels.

Oversteering can also occur when a lower-than-desired gear is selected at high speeds. When this occurs, in extreme circumstances, the rear wheels lock up. The weight of the car is then thrown forward and even a hint of a steering lock makes the car’s rear-end kick out and send the car into a slide.

Though front wheel cars understeer, they can also oversteer under certain conditions.
Though front wheel cars understeer, they can also oversteer under certain conditions.

The way to combat oversteering is very straightforward, in principle; but it can be difficult to master. As the rear of the car rotates, you need to apply opposite lock and gradually decrease throttle pressure. Here’s why this is difficult – you need to apply just enough steering lock to point the wheels in the direction of the slide. Apply too little lock and you will continue to spin as the back comes around. On the other hand, if you apply too much steering lock, the car will over-correct, resulting in a spin in the opposite direction.

All said and done, it is important to have good tyres because without that all your control and driving skills go out the window. If your only contact with the road are old bald rubbers, they are about as useful as a cricket bat in a gun fight. Get yourself a good set of tyres as the first line of defence and belt up every time you get into a car.

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