Ideally, when you turn the steering wheel, your front and rear tires will turn at a consistent rate. This will be the case so long as you are below the traction limit of your tires. But what happens when you exceed the traction limits of your tires? This is where Understeer, Oversteer, and Drifting come into play.
Understeer
Imagine that you when you are cornering, your rear wheels have plenty of traction but your front wheels lose traction. Since your front wheels don’t have any more traction to make the car turn, your car will continue to move in a straight line regardless of whether you turn the steering wheel more. This condition is known as Understeer. Alternatively, you might hear it referred to as “pushing” or “plowing.”
Correcting Understeer
The best way to fix understeer is slow the car down. To do so, you should straighten the steering wheel and get on the brakes. As described in The Friction Circle, there is a limit to the amount of grip of your tires. If you are understeering, you have exceeded your tires’ limit of traction. For the same reason that turning the steering wheel more will not make the car turn, hitting the brakes will not make the car slow down appreciably. To regain braking traction, you need to unwind the steering wheel, transitioning the gripping force from a sideways cornering force to a straight braking force. When you have bled of some speed, you can then finish turning through the corner. Though this is not the best Line to take through a corner, it is the safest and most effective way to deal with Understeer. If you are understeering, you are already off of the best Line, so just slow down as quick as possible so that you can quickly get back on the Line.
Oversteer
Oversteer is the exact opposite of Understeer. During a corner, your rear wheels lose traction before you front wheels. This makes your rear wheels travel in a straight line, since they no longer have the traction required to make the turn you have asked of them. But, since the front wheels have sufficient grip, the front of the car will continue to turn. The rear of the car will therefore rotate around the front of the car. If not corrected, the car will spin out completely.
Oversteer is significantly more dangerous than Understeer. Understeer just puts the car into a straight skid, while Oversteer can make the car spin off of the road completely.
There are several things which can cause Oversteer. These include giving the car too much throttle in a corner (Power Oversteer), braking while cornering (Brake Oversteer), and lifting off of the throttle abruptly in the middle of a corner (Lift Throttle Oversteer).
Correcting Oversteer
The first thing you should do when your car begins to oversteer is to turn into the spin. This is called Countersteer. E.g., if you are turning right, and your car begins to oversteer, turn the steering wheel to the left. If you are turning left, and your car begins to oversteer, turn the steering wheel to the right. Turning into the spin stops the front of the car from rotating around further, thereby helping to stop the spin.
Additional techniques to correct Oversteer depend on the drivetrain layout of your particular car. Front-Wheel Drive cars benefit from a steady application of the throttle. This will “pull” the front of the car forward and out of the spin. The downside to giving the car gas is that your speed will not bleed off as rapidly. So, if you cannot recover from your spin and you have been playing with the gas, you may hit whatever it is you hit harder. That said, it is better to use the throttle and stop a spin then to not use the throttle and hit something. Use caution and good sense, as with anything right?
Rear-Wheel Drive cars benefit from modulation of the throttle as well. 9 times out of 10, Oversteer in a RWD car will be from too much throttle (Power Oversteer). In this case, you want to give less throttle. This frees up acceleration traction that can be used for cornering traction to regain grip (see The Friction Circle). However, you don’t want to lift off of the throttle completely as, ironically, this can actually make the spin worse. Fully lifting off the throttle shifts weight off of the rear tires and onto the front tires. Less weight on the rear tires means less traction, and less traction means less grip to stop your spin. So, ideally you want to lift almost all the way off of the throttle to correct Oversteer in a RWD car.
In All-Wheel Drive cars, correcting Oversteer is a combination of the above techniques. The main tactic remains countersteering. What to do with the throttle is dependent on the specific car in question, its drivetrain layout, and torque bias. Some cars will act like a FWD car in a spin, and others will act like a RWD car. Only experimentation (in that big, safe, private parking lot you own) will let you get a feel for exactly how your car behaves in a spin.
4 Wheel Drifting
When both the front and rear wheels are slipping sideways at a constant rate, you are in a 4 wheel drift. It generally takes a very neutral-handling car under the right conditions to induce a 4 wheel drift. In most situations (even with neutral-handling cars), Understeer or Oversteer will be more prevalent.
To stop a 4 Wheel drift, you need to bleed off speed. If you remain at neutral throttle (and no, powering through a 4 wheel drift is definitely not neutral throttle), you will slowly bleed of speed as your tires slip. To stop a drift more quickly, treat the drift like understeer: straighten the wheel and get on the brakes. This gets you back to down to a speed your tires can handle better around that particular corner.
on March 2, 2007 at 6:01 pm Richard C. wrote:
“Oversteer is significantly more dangerous than Understeer. Understeer just puts the car into a straight skid, while Oversteer can make the car spin off of the road completely.” I’m sure I must be wrong on this but wouldn’t that partially depend on weigh distribution and if it’s front wheel, rear wheel or 4-wheel drive? For example what if it was a rear-wheel drive car heavy in the back- wouldn’t losing traction on the front cause the back of the car to spin toward the front? (And eventually spin out.) Or was is just that since there aren’t “many” rear-wheel drive cars with the engine in back anymore it’s inconsequential?
on March 3, 2007 at 1:02 am noah wrote:
Good question. There are many factors that can lead to understeer and oversteer, and the best way to correct them. Weight distribution is one of those factors, which I’ll explain a little more below. However, in the idealized example I was using in my article, the short answer is that no, the drivetrain and/or weight distribution cannot inherently turn understeer into oversteer.
Think of it this way. Imagine you are in a gigantic parking lot, driving in a circle. Now imagine that you lose all traction in the front. Since your steering wheels no longer have any grip, they cannot turn the front of the car. Thus, the car will travel in a straight line, and you will experience oversteer. If, instead of your front wheels losing traction, your rear wheels lose traction, then the front of your car will continue to turn and follow the circle, but your rear will continue in a straight line. This is Oversteer, and will put you into a spin if not corrected since the rear of the car does not turn with the front of the car.
It is important to note why Oversteer occurs, as this will help you understand why Understeer does not become Oversteer. Oversteer requires traction in the steering tires to introduce rotation to the car. With no rotation, there can be no Oversteer. Try locking up all 4 wheels sometime and you will see that the car just travels in a straight line.
Weight distribution comes into play in inducing Over or Understeer, and in how easy it is to correct. I’m going to write an article at some point about the finer points of this, but can give you a quick run down now. Basically, the tires at the heavier end have to work harder. A front-heavy car works the front tires harder, and reaches and exceeds their traction limit first. Thus, front-heavy cars tend to understeer more (all other factors being 100% equal, which they rarely are).
More important is what happens when you begin to Oversteer. With a rear-heavy car, there is now a lot of weight swinging out to the side. More weight has more inertia, and requires more grip to correct. Thus, rear-heavy cars can be more difficult to control in Oversteer.
And while most cars are either front or mid-engined, Porsche 911s are all rear-engined. So rear-heavy cars are a bit more common than you would think.
on April 1, 2007 at 10:37 pm The Pansy Patrol - Info for the 3000GT / Stealth Community wrote:
[...] As you know from reading Oversteer, Understeer, and 4 Wheel Drift, Oversteer is what happens when your rear tires lose traction before the front tires while the car is turning. This causes the car to begin to spin and, if not corrected, the car will spin out completely. Power Oversteer When most people think of Oversteer, they think of a very powerful rear-wheel drive vehicles spinning the rear tires by the sheer power of the engine. This is known as Power Oversteer. This is a typical (and amusing) means to induce Oversteer, but it is only one way to get your car sideways. [...]
on August 7, 2008 at 9:56 am The Pansy Patrol » Advanced Incident Management: What to do AFTER a Difficulty wrote:
[...] talked about the basics of oversteer and how to correct them, but now its time for a little more in-depth look at what exactly you should [...]
on August 7, 2008 at 9:56 am The Pansy Patrol » Advanced Incident Management: What to do AFTER a Difficulty wrote:
[...] talked about the basics of oversteer and how to correct them, but now its time for a little more in-depth look at what exactly you should [...]