Car Control refers to controling the car when it has been thrown out of it's balance and beyond the limits of grip. In this situation, the car is sliding out of control, and the driver needs to regain control. In this aspect, the term 'car control' is tricky, because the driver is essentially out of control. The ability to recover depends on the pace of driving before the slide, the driver's skill level, the car's setup and the road around us. The public roads give little to no clearance when sliding, so most skids are likely to end badly. The race-track offers a wider area for recovery, but when you drive at an actual racing pace, you are always using around 10 tenths of your car's abilities, at which pace, should the car break away, a recovery will be impossible.
This is the contradiction of car control: The normal road driver is too unskilled to master it, but the advanced drivers who are skilled in mastering it, are also skilled enough to avoid it, while the really skilled drivers (professional race car drivers), no matter how skilled, cannot control a slide that occurs at their driving pace on the track. So, there is no real answer other than prevention. While preventing a skid is easier than controling one that has occured, the tools used for both prevention and recovery, are identical, and we will explain them thuroughly here.
Why cars slide
If you remember the article about car dynamics, than you remember that the car has a certain amount of grip. The limit of a car's grip is where the car starts to slide. Demand too much of the car and it will kick back at you. However, since grip is formed at the point of contact between the tires and road, than we can say that the car is not sliding, it's tires are. This also means that there are different kinds of slides.
If either of the front wheels slide, the car is said to experience a "front tire skid" which is better known as "understeer." The logic behind the name could not be more clear: It's the front wheels that tilt into the corner when you turn the wheel, making the car change directions. When you ask too much of them, the slide. Since they slide, they cannot do their job as well. Given that their job is to turn the car into the corner, they will therefore make the car slide onward and out of the corner. The car would seem as if "refusing" to turn, and will take a wider arc and sometimes even feel like it's ploughing straight on.
The other kind of slide is when either of the rear wheels slide. At this case, the car is said to "oversteer." The reason for the name here is less obvious. The rear wheels are not tilted into the corner (leaving aspects of the toe angles aside for now), but as the car rotates into the corner, they are placed in an angle relative to where they were pointed to on the straight. This makes the rear wheels develop a "slip angle" which keeps the car in line with the front wheels. If they have too much grip they will refuse to go around and "push" the car into an understeer again, but if they have too little of grip they will swing aside (the car will "throw it's tail out," so to speak) and rotate the front of the car "too much" into the corner, hence the name oversteer. Another kind of slide is when the car is said to be neutral, sliding symetrically at the front and rear. The car will slide laterally out of line before transitioning into understeer or oversteer.
These skids occur in corners, but you can also get skids on the straight when you brake too hard without ABS (and the wheel lock up), when you accelerate too hard without traction control (and the wheels spin) and when you drive over a deep film of water and the car hydroplanes. These skids can occur in a straight line, but they just might cause the car to slide sideways.
Why the car slides
We need to deal with two contradicting concepts: Weight transfers and the friction circle, and I'll spare the math from you this time. The friction circle is the most basic theory of grip and car control on tarmac. It describes the overall grip capabilites of the tire and the net force it can produce. Basically, it states that each tire has an overall 100% of grip, which is divided between the forces working on it. Use 20% for acceleration and how much have you got left for steering? Just 80%. Use 50% for cornering and how much have you left for braking? 50%. By placing on either tire a demand that exceeds it's 100% of grip, you make it slide.
However, this model does not give you the whole truth. According to it, when we brake or accelerate, we won't be able to corner as well as we would if the car was to be fixated on a constant speed. But, there is more to a corner than just cornering. When we turn into the corner (i.e. from the point where the wheel is straight till right after it's fully turned into the corner) and we turn out of it (from fully turned and back to straight) the car is said to be experiencing a transient. During the transients, we can use the mass of the car to increase their effectivness.
If we carry just a fractional bit of braking during the transient of coming into the corner, the car will "nosedive" over it's front (which can be felt more noticably under strong braking) and over we will have more grip. In the corner, where we keep the steering at a fixed angle, we need to keep it on constant throttle, just strong enough so that the car is not slowing down or accelerating, just cornering. When we start to straighten out we increase the throttle to accelerate the car which "pulls" it out of the corner. We can say that in every part of the corner, there are two wheels which are the "critical wheels" for that part of the cornering process. During the change of direction into the corner, it's the two front wheels who have to tilt and turn the car into the corner. In the corner it's the two outside wheels, and coming out of the corner it's the two rear wheels that straighten the car up.
By doing this, we create weight transfers that push down on each of those wheels at each of the phases of the corner, giving them just that extra bit of grip: Brake to transfer the weight forward coming into the corner, balanced on throttle inside the corner, and accelerating to make it squat over it's two rear wheels coming out of it.
Another thing to learn about weight transfers is the way in which they occur. The graph below describes the manner in which a cornering force is loaded onto the car.
Stage 1 describes turn-in where the steering wheel is turned more and more tightly into the corner, untill the required amplitude is achieved, at which point a spike (described in 2) occurs. The more smooth is the driver, the smoother is the spike, as described in the second graph (illustrating a jerky driver). Afterwards the car is kept with the steering in the required angle, at which point the cornering force remains constant (3) and than the steering is retracted (4) as the cornering force fades out. At this point, there is a pendulum effect which creates a small spike of a cornering force in the other direction.
This is important to establish to the significance of smoothness and accuracy, but also to appreciate the phenomenon of resonance. Lateral weight transfers become more and more intense when you saw the wheel from side to side. The resonance will be greatest when you turn the wheel and, just at the spike, turn it in the other way. This creates a greater side to side weight transfer and induces oversteer.
Skids and Car Setup
While some people look favorly upon a car that behaves neutrally, all cars are set to understeer. It is the simple tendency of the moving object to maintain it's forward motion and refuse to turn. A car that would be neutral or oversteering could bearly be driven, and it would require a very complex and expensive setup. By "set to understeer" I do not mean that all you will get from your car is understeer. Every car can be made to exhibit each of the three characteristics. However, every car has a "natural tendency" which is revealed when the car is balanced. I.e. You keep the car on constant throttle, so that it is not slowing down or acceleration, and you turn into a corner at a speed just above it's ability to turn.
If, in this situation, when perfectly balanced on throttle, the car slides it's front wheels and pushes forward and out of the corner, it is said to have an inherent understeer. If it slides perfectly sideways on all four wheels, it's said to behave neutrally, and if it slides it's rear wheels and through it's back around the corner, it's said to oversteer. In these given situations, every car in the world would understeer. Besides being the natural and in-escapable physical tendency, understeer has various safety benefits over the other kinds of slides. Perhaps the main advantage is that it is "self resolving." Once a car starts to understeer, the slide fades out progressively even if the driver does little to nothing in an attempt to recover. The car fails to take a sharp corner, so it pushes out, this makes the corner wider and the car can turn again. Also, the understeering car is losing speed, which helps reduce excess speed and to create a weight transfer over the front wheels. Oversteer is the exact opposite: It rotates the car more and more into the corner, so unless you react very quickly you will spin.
Another advantage was very important in older cars and is still important in racing, and it is the matter of feel. The two front wheels are closer to the driver, and directly connected to him via the steering mechanism. Therefore the slide can be felt prematurely as a certain "numbness" of the wheel and the recovery input will come faster. When the slide is at the rear wheels (oversteer) the driver has no direct linkage to it. If all four wheels are sliding, then no axle "breaks away" relative to the other and the skid is even less distinctable.
There are other advantages of safety, like a more intuitive manner of recovery (which will get to later), more tolerance to bad recovery inputs and, at the worst case scenario, less acute of a crash as the understeering car hits the obstacle head on, while the oversteering car might hit it sideways. In racing, there are additional advantages: The driver wants to stay on full throttle for as long as possible so, coming up to the corner, he wishes to brake as late as possible, which he can achieve by braking very hard, but also by carrying this braking effort into the corner. In an oversteering car this is simply impossible to perform as the car would spin. Also, professional racing cars are rear wheel driven, so understeer inside the corner would mean that there is still some grip left in the rear wheels, allowing for stronger acceleration to take place coming out of the corner.
This is just the right moment to talk about car setup, beginning with the drivetrain. A front wheel drive car is what most people drive on. This car shares the same steering mechanism where the two front wheels turn the car into the corner, but also have those wheels connected to the engine. Also, as with all cars that are not rigs, most of the braking effort lies on the front too. The engine itself is in the frontal portion of the car, loading it with more mass. It is clear how this design is prone to understeer. A front wheel driven car will always understeer when you are on the gas, it can only oversteer or slide neutrally when you are off of the gas or braking.
A rear-wheel driven car puts the acceleration on the rear wheels, forming a segregation of the acceleration and cornering vector. These kind of cars naturally oversteer as well, but they can also experience oversteer under too much acceleration, and not just when off-throttle/braking. All-wheel drive cars form a certain combination, but they can also slide when powered, like a rear wheel drive.
Another important callibration is the suspension. A soft suspension gives you more grip, so a softer front means less understeer and a greater likelihood of oversteer. In a track car, the opposite is true and the stiffer axle is the grippier one. The main difference is about the feel of the slide. A stiffer car reacts more instantly to the driver. This can make it "break away" more suddenly, but with more feel and more control over the slide itself (as the car also reacts more quickely to the recovery inputs). A soft car tranistions into a slide more progressivelly, but with less feel and less control.
The last element is weight distribution. A heavier axle is supposed to be less grippy, but playing around with the tires and tire pressure can exchange the bad effect for an overall increase of grip. However, once sliding, the heavier axle will be harder to control. Another effect of weigh distribution is the car's center of pollar movement. Some front wheel drive cars have their engine placed far forward, in front of the front axle. This makes the car rotate into the corner around an imaginary pivot in it's nose, generating more understeer. A car with a rear engine is going to suffer from more understeer when on constant throttle, but the slightest action to make it oversteer will result in an immediate and mighty oversteer.
This is the right place to mention the function of passive rear steering. This is a function of the rear suspension of some front-wheel driven cars, which does one of two things: The first is to reduce understeer. The car is "allowed" to experience a certain slight amount of understeer. Once you accelerate or steer more sharply, it makes the outside rear wheel "toe" under the load. The wheel will in fact be "turned" out of the corner and this will turn the back of the car around. This feels as a momentary break-away of the tail, much like oversteer, only that it will not develop into a spin without any further provocation. It will simply "step out" momentarily and turn you around the corner. The other function in some cars is to make the wheel "toe in" and resist any initial oversteer. The sensating will be identical. It is simply a means that many car designers use to make their road cars more safe or less "frisky."
Another thing is the "roll angle" of the car's body. When the car turns, some of the force which pushes it out of the corner (which creates slides) is turned into torque that tries to roll the car over instead of pushing it sideways. This torque makes the car lean to the outside of the corner, over it's springs. This brings us to the subject of rolling over. For a car to roll over, it needs to have enough grip to fully compress it's suspension and to reach such an angle as to risk a rollover.
However, most road cars, even most SUV's, are made to slide quite a bit before they reach such a roll angle. The car will always grip more on the verge of sliding than when sliding, so it cannot create a bigger roll angle and can't roll over. Rolling over is the physical way of the car not to roll over. Beware, though, if jerked repeadetly from side to side, or it if hits even a very small obstacle on the road (even a small unnoticed slot in the tarmac or a bit of sand) might risk you in a roll-over. Still, some cars lean very sharply over the suspension, and other even "lift" one wheel (normally a rear wheel), but these are normal functions of the suspension of those cars, either due to the length of the spring or the relative stiffness of the anti-roll bar. It does not mean that the car is due to roll over.
If a car begins to roll over, it might be "saved" by steering against it. This neutralizes a steering angle created by the camber of the outside wheel as it pivots relative to the surface, but does not necessarily works. A better solution is to avoid the roll over, and to brace yourself towards and impending one. The solution during an actual roll over begins prematurely by being well placed inside the car (adjusting the proper driving position) and having the seatbelt properly placed over your body. Once a roll-over is initiated, place the hands at an X-pattern over your chest, and apply support with the left foot.
Once you are rolled over, getting out requires some acrobatics. The seatbelt is going to carry your whole weight, which will act against it's spring and make it lock. You need to free your legs and put them against the crumpled ceiling and push against it, which will allow you to free yourself from the seatbelt and roll out of the car safely.
Causes of Slide
Understeer is caused by either of the following:
1. Excessive speed: If you turn into the corner at too fast a speed, the car will understeer. It simply won't manage to complete the transient and turn into the corner in time.
2. Coarse Steering: Steering more sharply and ubruptly increases the understeer tendency. In cars with passive rear steering, the car's back end might feel as if it "swings" aside for a moment and tuck you into the corner, but this will not develope into an actual oversteer unless you slow down or brake.
3. Excessive Braking: Braking shifts the weight forward and gives the front more grip to reduce the understeer, but without feel, strong braking will reduce the grip because the front wheels use all too much of their overall grip "budget" for braking instead of cornering. Under very strong braking, the car's wheels will lockup and the car will not turn.
4. Excessive Acceleration: Understeer caused due to insensitive acceleration in the corner. The acceleration will shift weight off of the front wheels and induce understeer. In a front-wheel drive, some of the cornering force will also be used for acceleration, further reducing grip.
Oversteer is caused by:
1. Excessive deceleration: Slowing down shifts weight forward, leading to a light rear which can slide. At the extreme it can be seen as the back end of the car rendered airborne and swinging aside. Of course deceleration can also reduce front end grip, as it be used to brake instead of turning, leading to understeer, but this usually occurs under much stronger a deceleration, or such that occurs mid-corner. The required deceleration for oversteer can be achieved by going off of the gas, braking lightly, jerking the car from side to side, or steering sharply when off-throttle.
Coarse steering makes the car experience an initial understeer which transitions into oversteer because the front wheels generate more friction with the road. Likewise, jerking off of the gas will produce sharper of an oversteer than when easing off of it gradually. Another thing that can help decelerate the car is the handbrake. In most cars, it actuates only the brakes on the rear wheels, so you slow down the car and overload the rear wheels with braking forces simultanously.
2. Excessive Acceleration: Acceleration leads to more speed and less front downforce, thus creating understeer. But, in a rear-wheel drive car, the engine force loads the rear wheels with a force of acceleration. In highly strong acceleration, powerfull rear or all-wheel drive cars (as well as on slippery surfaces) the car might experience "power oversteer."
Neutral handling occurs when the driver enters a corner at just the right speed with a slight braking force. Any speed over this one will result in understeer and any speed below it will create oversteer. At any point, there is such a thing as "understeer transient." Before you can be turning, you have to turn-in. Turn-in is defined as the whole area of the corner from where the wheel is straight to just after you finished turning the wheel into the corner. During this stage the car is said to be changing directions and yawing into the corner.
The importance of this stage is that it is always defined as understeer. In other words, the car cannot experience oversteer or neutral handling before you finished turning the wheel into the corner. Some drivers try to induce oversteer by the methods above and fail just because of timing: The pull the handbrake before turning the wheel, as an example. The oversteer will be most powerfull when the provocatice action of jerking off of the gas/braking/handbrake and alike is aligned directly with the point where you finish turning into the corner, a mere fraction of a second just after the wheel is fully turned into the corner.
Prevention of Skids
Step one, don't trust the electronics. I wrote an article in the past where I explained roughly where the limitations of stability control systems lay. It's not that they are inefficient, they are highly effective. In fact, maybe that article stressed the limitations of ESP too much as to give a reliable picture of it's abilities, but it does not change the fact that it is your job to ensure the car does not slide. Remember, stability control straightens the car out of the slide, once it has occured (and lasted for a few tenths of seconds), but you can prevent the slide altoghther.
The next step is to maintain the car: Fit it with four identical tires, inflate them regularly and replace them whenever they are even moderately aged or worn. Replace old dampers to keep the car's suspension working properly. These moves will increase the grip levels and allow the car to remain further from the point of breaking away.
But the most important step is to adjust the speed to the conditions. If you remember the formal expression for the critical cornering grip, you remember than it changes upon variants of coefficient of friction, gravity, cornering radius and speed. The road surface, load in the car, suspension and tires change the coefficient of friction. The exact location on the earth changes the variation of gravity slightly, and the cornering radius depends on the corner and the line you take through it.
However, speed changes the cornering force much more dramatically than any of the above, since the velocity variant is changed by the square root. Also, as speed increases, the tires are made to operate in larger slip angles, which change the steering angles and tighten the radius of the corner. Speed can also effect the coefficient of friction on wet surfaces or when it makes tires generate heat. Overall, a slower corner entry speed is the first move to ensure cornering without sliding. Remember the "Slow in, Fast out" rule.
With that being said, managing the following steps can increase the "reserve" by 30% to twice as before. Other than maintaining the corner, proper loading is also important. The loaded axle should have less grip, but once the tire pressure is increased to match the added load, the effects cancel each other out and to a certain extent the grip levels will increase. However, the car will brake less effectivelly and have more transient understeer (take longer to react to the steering). Anyhow, try to put any additional load as securedly as possible and as low as possible inside the car, and distributed equally left to right. It's also best to try and put the cargo between the front and rear axles rather than on the car's extremities.
Choosing the right line also helps monitor the cornering radius. Taking a wide cornering line, as they are described in earlier articles, helps increase the cornering radius to increase grip levels in the corner or coming out of it.
Smoothness and accuracy also form a hugh shift in the ability to corner without sliding. Some drivers exaggerate, and can be seen steering very slowely, especially in slippery conditions. You need to maintain a gradual but decisive steering input. The more tight is the corner, the slower is the approach and the more quickely can the steering be applied and still produce a smooth result. Some cornes require a line where you must steering sharply coming into them, slightly compromising the smoothness of turning in for the sake of better vision through it.
Next comes mananging the weight transfers, which we managed earlier. Brake before the corner, and enter the bend with the brakes so the weight is biased forward. Once you finished turning the wheel into the corner, keep the car on constant throttle (in a constant speed) and accelerate out as you straighten the steering. However, if you brake into the corner or accelerate out it without smoothness and accuracy, you will reduce the grip rather than increase it. Too much braking loads the front wheels with a braking force which "eats up" grip that could otherwsie be used to steer. Acceleration out of the corner should also be as slight as possible.
The next stage is to get to know the car. Some cars have a heavy front-end where the engine is situated in front of the front axle. As a rule of thumb, these cars will experience greater understeer and require the driver to follow the above instructions much more dogmatically. Other cars have slightly softer suspensions and a more balanced weight distribution. These cars are more controlled over a larger envelope of performance, and can be driven slightly more decisivelly with a bit less smoothness than the former. Getting to know the car also referrs to the limts: Knowing when you car is likely to understeer or oversteer and how sharply.
For instance, if I drive a Peugeot 206 I know that the car is very nicely balanced and can be provoked into an oversteer under relatively light braking in the corner when near the limit, or even just by "decisivelly" lifting off of the gas. I also know that it breaks away more gradually and controlably, and allows to "play" along the corner by moving the weight forward and back to induce oversteer and understeer at will.
Reading the road surface is another skill for avoiding skids. One of the most acute causes of slides is a sudden change of the grip levels. This can be caused by thing, see through layer of ice left on a certain part of the road (usually under the shade), so called "black ice", as well as by occasional big slips of oils on the road. Potholes and glass shards can also lead to similar results. The solution begins by looking up to the furthest possible distance ahead. At this distance, you need to recognise any change of the road surface. Ice can be seen by it's shine, and oil can be seen as a range of greasy colors.
When you get over such a low grip area, the front wheels are the first to contact it and slide. But a front-wheel slide (understeer) is self solving so it doesn't last. But once the rear wheels get over the slippery substance they break away and an oversteer is likely to happen, especially when the front wheels leave the slippery area and grip again. The solution is to detect this slippery area is the distance. At this point you need to slow down as much as possible, considering the available distance and the traffic behind you and try to get around it. If you can't get around it, try stopping before it. If not possible, drive over it at the lowest possible speed, the straightest possible line and on constant throttle. Rear wheel drive cars are best declutched or flicked into neutral.
Getting a Feel for the slide
The key point of recovering from slides, other than the actual recovery input, is to apply it at the right time and in the right amount. Knowing the foundementals of car dynamics (as they are described above) and knowing your own car in particular, helps to anticipate how the car is likely to slide: If I brake through a corner in the car I described above I'm likely to recieve oversteer. If I am on constant throttle I will recieve slight understeer in any case. If there is a slight downhill incline, I will not only have less grip, but also a greater tendency towards oversteer.
The second stage is to acquire a feel for slides. If you feel the slide, you can know it's coming and apply a correction before you actually see it. This allows to react more quickely and recover before the slide develops into an actual drama. I stated before that understeer is considered safer as it can be felt through the steering. And indeed, understeer can be felt as light and "numb" steering. Good steering feel and a good grip of the wheel allows to identify this more quickely. Under power, many front-wheel drive cars actually suffer from stiff steering, due to so-called "torque steer" where the power can be felt as pressure that makes the wheel want to straighten up.
Oversteer is more misleading in this way. It can be felt through the buttocks by seating properly, mainly by placing your buttocks as snuggly into the corner of the seat as possible and using your left foot to apply pressure against the footrest. It also has a steering feel, albeit a treacherous one: The oversteer makes the rear end slide. This creates a moment where the front wheels are no longer experiencing any side force, and than they start developing a side force in the other direction, which can again be felt as pressure on the wheel, which tries to make it rotate all the way in the other direction.
Sight also helps. By looking into the corner and beyond it, as far ahead as possible, we can notice any slight changes more rapidly. If you are looking five feet ahead and the car slides aside, you will not notice it as much. But, if you are looking 400 feet ahead, once the car starts to slide off very slightly, your point of focus is shifted much more dramatically. Once this is felt, it is important to keep on using your vision. Most drivers look at what they try to avoid and steer away from it. This breeds panic and panic input by trying to steer away from the obstacle, while having little of an idea as to how much to steer. However, if you look in the direction you want to go to and steer towards where you do want to go, you will know to gauge the right amount of steering to get you out.
Another note: Cars can oversteer (or be made to oversteer) in one of two ways: The first can be felt as a subtle, gradual breakway of a tail, where the car's back end seems to gradually drift aside. This is far more controlable and desired in drifting cars and in general. The second case is when the car breaks away violently and suddenly, which is often not controlled at all. In any case, the mistake when recovering from oversteer is that drivers let the oversteer rotate them into the corner and than correct it. Do not. Once the oversteer is felt, apply a corrective input and THAN work on getting out of the corner.
Recovering from Slides
Only after you learned how to avoid a slide and how to know and feel when it is going to happen, you are ready to learn how to recover from it. This requires a lot of skill, such skill which cannot be acquired by training by yourself or by a short skidpad tuition, but let's leave the subject of training for later and touch the actual means of recovery.
A car does not skid if the driver does not do something that makes it to. So, if the skid occured, the driver did something to cause it. So, in order to recover, he needs to do the opposite, simple. I'll tell you (as you should already know) what doesn't cause a slide: the mere action of turning into the corner. There is always something else: excessive speed, uprupt steering input, excessive braking or acceleration, etc. So, the correction of the slide is never going to be to simply steer out of it. If the slide is caused by excessive speed (which always means understeer) than the solution is to wipe off that speed. If the slide is caused by excessive braking, the solution is to remove this excess braking. Of course you also need to steer the car towards the right direction, but this is done automatically by your eyes if you only look towards the right direction (as I noted above).
In case of understeer, you need to reduce the speed and put more downforce on the front wheels. So, back somewhat off of the pressure on the gas. If you must let up the throttle all toghether, be gentle or otherwise you will create a "spike" of engine braking which will make it snap into an oversteer. Sometimes you will also need to brake with feel: Enough braking to put more load on the front and shake off excess speed, but not too much as to overload the front wheels with braking forces or locking them.
The solution seems very natural for a slide: The car starts ploughing, you let go of the gas and brake with feel and you recover. It is important, though, to practice easing the gas progressively enough (exactly how progressively depends on the corner and car) and braking with enough feel to get out of the understeer as quickly as possible. There is another thing to practice and that is the steering. Like I said, steering out of the understeer is not going to work and yet most people will simply turn the wheel tighter and tighter into the corner.
When the car turns the wheels develop a slip angle between the direction the wheels are turned and their actual path of rolling. When the car starts understeering it means that the front slip angle is too large. If you steer more, the tires are still sliding in the same direction, but turned ever more sharply, so the slip angle is bigger. It's like the model of the friction circle: You just load the sliding tire with extra demands and hence increase the understeer.
It's not that it can't work. In fact, it might work in most cases. Understeer is self-solving, so increasing it makes the front tires slow down even more and the car will eventually regain grip. The problem is that this is a much less efficient method of recovery, it requires extra space which isn't normally available on the road. Also, the recover is not going to be as smooth and linear. The car will slide harder, untill eventually tighten the line back up at once, and possibly transition sharply into an oversteer at the least preferable time.
The actual solution is actually to reduce the steering angle slightly. There is a certain angle (say, 6 degrees) between where the car is sliding to and where the front wheels are pointing towards. If you reduce the steering angle (say, by 2 degrees) than the car doesn't need to tighten the line by just as much (by four degrees instead of six). Once the car has gained grip again you can tighten up the extra amplitude more quickely and smoothly.
The problem is to have the discpline to slightly reduce the steering input instead of tightening it up. In order to do this you don't only need to look in the right direction, you also need to apply the recovery input very quickely, before the car actually starts to take a wider line that forces you turn more tightly. You need to feel the slide and anticipate it, and than ease off of the gas and brake with feel while slightly retracting the steering lock. The steering should than regain it's normal feel and be "heavier", at which point you need to gently turn the wheel back to the required angle.
Oversteer is more complex. The natural response is again to brake, but this shifts more weight forward and off of the sliding rear wheels. Another natural respone is again to steer out of it by turning the wheel against the direction of the corner. This would be efficient if the cause of the slide was that you steered in the wrong way or too much, but oversteer does not occur because you over-steer, it is a result of a forward weight transfer or excessive torque in the rear wheels (in a powerfull rear-wheel drive car). The solution is to reduce those factors.
If the cause is a forward weight transfer, than we need to transfer it back onto the rear wheels, so we actually need to accelerate (not a very natural response when the car is sliding) which will pull the car forward and back to straight. This is particularly efficient in front-wheel driven cars, where we can harness the power of the engine purely to transfer weight to the rear and regain grip in the back. So you accelerate forward and reduce the steering input (or straighten it completly) and get the car to grip again. In a rear-wheel driven car, you can't use the engine's power as much, so you need to keep the car on constant throttle (just like you should do mid-corner) and steering agains the corner. Eventually the car will "take a set" and than you will make a second steering move and straighten the steering again.
The latter manner of correction is also effective when the slide occurs under excessive power (which can only happen in rear-wheel driven cars anyway). So you need to counter-steer towards the direction you want to go to (which is against the corner) while keeping the car on constant throttle and than straighten the steering back. By keeping the car on constant throttle you keep the weight of the car balanced, but without putting torque through the rear wheels. If you accelerate or decelerate you will recieve a non-linear steering response. The car will take longer to react to the steering, and than it will react all too sharply and spin you around in the other direction.
Based on the effect of resonance, the slide in the other direction is normally going to be much stronger and more dangerous than the first. The car is not likely to have any run-off area towards the outside radius of the corner, making it immediately move into the way of oncoming traffic or off of the road. The slide itself will be much more potent and often impossible to recover from. Besides, you have just steered the car sharply in one direction, only to be forced to undo the steering and turn it ever more sharply towards the other direction, all within a much reduced time spawn than before.
This is also why countersteering in front-wheel driven cars is best avoided. If you react quickely enough, or within a reasonable time spawn, you shouldn't have to countersteer. In powerfull cars, especially in sharp corners or on slippery surfaces, you can hold the wheel straight and accelerate hard enough to spin the front wheels which will push them back on the right line without countersteering. If you do need to countersteer, you again need to keep the car on constant throttle, but this is best avoided.
The exception is when the car is aquaplaning over a deep film of water or sliding over very polished ice. These situations create very little grip, as you can experience on epoxy skidpads too. In these conditions, trying to use weight transfer is not going to be effective. So there is another solution: You brake before the corner, apply constant throttle before the corner and all the way through it untill after you are perfectly straight and stable after the corner. If the car slides, you apply the clutch and steer out of it. If you try to accelerate out of the oversteer, you will spin the front wheels too much and lose front traction too. If you try to brake out of an understeer, you will lock the front wheels and the understeer will prevail.
Be declutching you allow the wheels to rotate freely and return to normal rolling motion and get over the slide. This is highly inefficient on most surfaces, only to be used when no practical grip is not existent. On these surfaces, emergency braking without ABS is to be done by pumping the brakes, unlike on any other situation.
Another situation where you need to go not following the book, is when you are not skilled enough or when the slide is beyond your control. The solution here is simple: Brake as hard as possible, as early as possible. After pressing the brake, press the clutch, if possible, and straighten the steering. This can help to stop you or reduce speed to a point where you might be able to recover from later.
Training Car Control
You can't teach yourself how to control a car in it's limits. You will want to do X, but you will do Y and think you did Z, where actually you would need to think and do something completely else. If you do get it right, you will not achieve the necessary control you will with some sort of training. Almost all activities which are considered a competitive sport requires a trainer. There are several ways of teaching car control:
The first method is a skidpad. The skidpad is made by applying a seal of epoxy onto a bitumen surface. Once soaked with water, the epoxy offers grip levels which are extra ordinarily low. The car transitions at once from full grip, higher than typically possible on the road, to a state of full blown sliding when you go onto the surface is which likely to be more slippery than any snow or grease you will tackle in a lifetime of driving. The correction input is also different (by applying the clutch) and the car is likely to illustrate a highly different handling characteristics. Some skidpads I've seen even use a plate that throws the car's rear wheels aside. Not very realistic.
A better method of training is called the SkidCar. This is a surprisingly sophisticated piece of engineering, formed as a cradle with four wheels that are allowed to run indepently, as they are installed over a car. The "cradle" is hydraulic and can, by the command of the instructor, who is sitting inside of it with a control, lift it's front or rear somewhat, and elevate the front or rear of the car, simulating reduced grip and imitating a wide range of road surfaces: Dry, wet, greasy, sand, snow, ice. The result is physically identical to the "real deal" and the modern devices don't intefere with the functions of the car's suspension.
This allows to practice all of the things we said above: You can just drive it around, and work on avoiding the slides, identifying them once they occur and controling them at that point. You acquire a feel for the slides through the steering and chassis, and control the slides. It is important, though, to practice a wide range of cars, including front-wheel driven, rear-wheel driven, all-wheel drive and cars with different weight distribution and a different suspension design.
The practice needs be further polished by doing some of it in the trainee's own road car, on tarmac, tight gravel and ice. These conditions allow to experience all of the ranges of grip, and a more progressive and sharp handling, while getting to know your own car: The driving style it likes, the cases where it slides and how it slides, and with what perliminary "warnings." Of course your tires won't like the part done on tarmac.
This whole ordeal should take at least two tuitions over two days, and it requires all skills of proper seating, steering and use of vision need to be in place before it, to reach a sufficient level of skill, which by itself needs to be maintained by a short practice once every few months at least, and an occasional practice with a trainer. Still, it's not super human to achieve a sufficient skill, and it's something that can help increase the safety of the driver, even with stability control systems.
This is the contradiction of car control: The normal road driver is too unskilled to master it, but the advanced drivers who are skilled in mastering it, are also skilled enough to avoid it, while the really skilled drivers (professional race car drivers), no matter how skilled, cannot control a slide that occurs at their driving pace on the track. So, there is no real answer other than prevention. While preventing a skid is easier than controling one that has occured, the tools used for both prevention and recovery, are identical, and we will explain them thuroughly here.
Why cars slide
If you remember the article about car dynamics, than you remember that the car has a certain amount of grip. The limit of a car's grip is where the car starts to slide. Demand too much of the car and it will kick back at you. However, since grip is formed at the point of contact between the tires and road, than we can say that the car is not sliding, it's tires are. This also means that there are different kinds of slides.
If either of the front wheels slide, the car is said to experience a "front tire skid" which is better known as "understeer." The logic behind the name could not be more clear: It's the front wheels that tilt into the corner when you turn the wheel, making the car change directions. When you ask too much of them, the slide. Since they slide, they cannot do their job as well. Given that their job is to turn the car into the corner, they will therefore make the car slide onward and out of the corner. The car would seem as if "refusing" to turn, and will take a wider arc and sometimes even feel like it's ploughing straight on.
The other kind of slide is when either of the rear wheels slide. At this case, the car is said to "oversteer." The reason for the name here is less obvious. The rear wheels are not tilted into the corner (leaving aspects of the toe angles aside for now), but as the car rotates into the corner, they are placed in an angle relative to where they were pointed to on the straight. This makes the rear wheels develop a "slip angle" which keeps the car in line with the front wheels. If they have too much grip they will refuse to go around and "push" the car into an understeer again, but if they have too little of grip they will swing aside (the car will "throw it's tail out," so to speak) and rotate the front of the car "too much" into the corner, hence the name oversteer. Another kind of slide is when the car is said to be neutral, sliding symetrically at the front and rear. The car will slide laterally out of line before transitioning into understeer or oversteer.
These skids occur in corners, but you can also get skids on the straight when you brake too hard without ABS (and the wheel lock up), when you accelerate too hard without traction control (and the wheels spin) and when you drive over a deep film of water and the car hydroplanes. These skids can occur in a straight line, but they just might cause the car to slide sideways.
Why the car slides
We need to deal with two contradicting concepts: Weight transfers and the friction circle, and I'll spare the math from you this time. The friction circle is the most basic theory of grip and car control on tarmac. It describes the overall grip capabilites of the tire and the net force it can produce. Basically, it states that each tire has an overall 100% of grip, which is divided between the forces working on it. Use 20% for acceleration and how much have you got left for steering? Just 80%. Use 50% for cornering and how much have you left for braking? 50%. By placing on either tire a demand that exceeds it's 100% of grip, you make it slide.
However, this model does not give you the whole truth. According to it, when we brake or accelerate, we won't be able to corner as well as we would if the car was to be fixated on a constant speed. But, there is more to a corner than just cornering. When we turn into the corner (i.e. from the point where the wheel is straight till right after it's fully turned into the corner) and we turn out of it (from fully turned and back to straight) the car is said to be experiencing a transient. During the transients, we can use the mass of the car to increase their effectivness.
If we carry just a fractional bit of braking during the transient of coming into the corner, the car will "nosedive" over it's front (which can be felt more noticably under strong braking) and over we will have more grip. In the corner, where we keep the steering at a fixed angle, we need to keep it on constant throttle, just strong enough so that the car is not slowing down or accelerating, just cornering. When we start to straighten out we increase the throttle to accelerate the car which "pulls" it out of the corner. We can say that in every part of the corner, there are two wheels which are the "critical wheels" for that part of the cornering process. During the change of direction into the corner, it's the two front wheels who have to tilt and turn the car into the corner. In the corner it's the two outside wheels, and coming out of the corner it's the two rear wheels that straighten the car up.
By doing this, we create weight transfers that push down on each of those wheels at each of the phases of the corner, giving them just that extra bit of grip: Brake to transfer the weight forward coming into the corner, balanced on throttle inside the corner, and accelerating to make it squat over it's two rear wheels coming out of it.
Another thing to learn about weight transfers is the way in which they occur. The graph below describes the manner in which a cornering force is loaded onto the car.
This is important to establish to the significance of smoothness and accuracy, but also to appreciate the phenomenon of resonance. Lateral weight transfers become more and more intense when you saw the wheel from side to side. The resonance will be greatest when you turn the wheel and, just at the spike, turn it in the other way. This creates a greater side to side weight transfer and induces oversteer.
Skids and Car Setup
While some people look favorly upon a car that behaves neutrally, all cars are set to understeer. It is the simple tendency of the moving object to maintain it's forward motion and refuse to turn. A car that would be neutral or oversteering could bearly be driven, and it would require a very complex and expensive setup. By "set to understeer" I do not mean that all you will get from your car is understeer. Every car can be made to exhibit each of the three characteristics. However, every car has a "natural tendency" which is revealed when the car is balanced. I.e. You keep the car on constant throttle, so that it is not slowing down or acceleration, and you turn into a corner at a speed just above it's ability to turn.
If, in this situation, when perfectly balanced on throttle, the car slides it's front wheels and pushes forward and out of the corner, it is said to have an inherent understeer. If it slides perfectly sideways on all four wheels, it's said to behave neutrally, and if it slides it's rear wheels and through it's back around the corner, it's said to oversteer. In these given situations, every car in the world would understeer. Besides being the natural and in-escapable physical tendency, understeer has various safety benefits over the other kinds of slides. Perhaps the main advantage is that it is "self resolving." Once a car starts to understeer, the slide fades out progressively even if the driver does little to nothing in an attempt to recover. The car fails to take a sharp corner, so it pushes out, this makes the corner wider and the car can turn again. Also, the understeering car is losing speed, which helps reduce excess speed and to create a weight transfer over the front wheels. Oversteer is the exact opposite: It rotates the car more and more into the corner, so unless you react very quickly you will spin.
Another advantage was very important in older cars and is still important in racing, and it is the matter of feel. The two front wheels are closer to the driver, and directly connected to him via the steering mechanism. Therefore the slide can be felt prematurely as a certain "numbness" of the wheel and the recovery input will come faster. When the slide is at the rear wheels (oversteer) the driver has no direct linkage to it. If all four wheels are sliding, then no axle "breaks away" relative to the other and the skid is even less distinctable.
There are other advantages of safety, like a more intuitive manner of recovery (which will get to later), more tolerance to bad recovery inputs and, at the worst case scenario, less acute of a crash as the understeering car hits the obstacle head on, while the oversteering car might hit it sideways. In racing, there are additional advantages: The driver wants to stay on full throttle for as long as possible so, coming up to the corner, he wishes to brake as late as possible, which he can achieve by braking very hard, but also by carrying this braking effort into the corner. In an oversteering car this is simply impossible to perform as the car would spin. Also, professional racing cars are rear wheel driven, so understeer inside the corner would mean that there is still some grip left in the rear wheels, allowing for stronger acceleration to take place coming out of the corner.
This is just the right moment to talk about car setup, beginning with the drivetrain. A front wheel drive car is what most people drive on. This car shares the same steering mechanism where the two front wheels turn the car into the corner, but also have those wheels connected to the engine. Also, as with all cars that are not rigs, most of the braking effort lies on the front too. The engine itself is in the frontal portion of the car, loading it with more mass. It is clear how this design is prone to understeer. A front wheel driven car will always understeer when you are on the gas, it can only oversteer or slide neutrally when you are off of the gas or braking.
A rear-wheel driven car puts the acceleration on the rear wheels, forming a segregation of the acceleration and cornering vector. These kind of cars naturally oversteer as well, but they can also experience oversteer under too much acceleration, and not just when off-throttle/braking. All-wheel drive cars form a certain combination, but they can also slide when powered, like a rear wheel drive.
Another important callibration is the suspension. A soft suspension gives you more grip, so a softer front means less understeer and a greater likelihood of oversteer. In a track car, the opposite is true and the stiffer axle is the grippier one. The main difference is about the feel of the slide. A stiffer car reacts more instantly to the driver. This can make it "break away" more suddenly, but with more feel and more control over the slide itself (as the car also reacts more quickely to the recovery inputs). A soft car tranistions into a slide more progressivelly, but with less feel and less control.
The last element is weight distribution. A heavier axle is supposed to be less grippy, but playing around with the tires and tire pressure can exchange the bad effect for an overall increase of grip. However, once sliding, the heavier axle will be harder to control. Another effect of weigh distribution is the car's center of pollar movement. Some front wheel drive cars have their engine placed far forward, in front of the front axle. This makes the car rotate into the corner around an imaginary pivot in it's nose, generating more understeer. A car with a rear engine is going to suffer from more understeer when on constant throttle, but the slightest action to make it oversteer will result in an immediate and mighty oversteer.
This is the right place to mention the function of passive rear steering. This is a function of the rear suspension of some front-wheel driven cars, which does one of two things: The first is to reduce understeer. The car is "allowed" to experience a certain slight amount of understeer. Once you accelerate or steer more sharply, it makes the outside rear wheel "toe" under the load. The wheel will in fact be "turned" out of the corner and this will turn the back of the car around. This feels as a momentary break-away of the tail, much like oversteer, only that it will not develop into a spin without any further provocation. It will simply "step out" momentarily and turn you around the corner. The other function in some cars is to make the wheel "toe in" and resist any initial oversteer. The sensating will be identical. It is simply a means that many car designers use to make their road cars more safe or less "frisky."
Another thing is the "roll angle" of the car's body. When the car turns, some of the force which pushes it out of the corner (which creates slides) is turned into torque that tries to roll the car over instead of pushing it sideways. This torque makes the car lean to the outside of the corner, over it's springs. This brings us to the subject of rolling over. For a car to roll over, it needs to have enough grip to fully compress it's suspension and to reach such an angle as to risk a rollover.
However, most road cars, even most SUV's, are made to slide quite a bit before they reach such a roll angle. The car will always grip more on the verge of sliding than when sliding, so it cannot create a bigger roll angle and can't roll over. Rolling over is the physical way of the car not to roll over. Beware, though, if jerked repeadetly from side to side, or it if hits even a very small obstacle on the road (even a small unnoticed slot in the tarmac or a bit of sand) might risk you in a roll-over. Still, some cars lean very sharply over the suspension, and other even "lift" one wheel (normally a rear wheel), but these are normal functions of the suspension of those cars, either due to the length of the spring or the relative stiffness of the anti-roll bar. It does not mean that the car is due to roll over.
If a car begins to roll over, it might be "saved" by steering against it. This neutralizes a steering angle created by the camber of the outside wheel as it pivots relative to the surface, but does not necessarily works. A better solution is to avoid the roll over, and to brace yourself towards and impending one. The solution during an actual roll over begins prematurely by being well placed inside the car (adjusting the proper driving position) and having the seatbelt properly placed over your body. Once a roll-over is initiated, place the hands at an X-pattern over your chest, and apply support with the left foot.
Once you are rolled over, getting out requires some acrobatics. The seatbelt is going to carry your whole weight, which will act against it's spring and make it lock. You need to free your legs and put them against the crumpled ceiling and push against it, which will allow you to free yourself from the seatbelt and roll out of the car safely.
Causes of Slide
Understeer is caused by either of the following:
1. Excessive speed: If you turn into the corner at too fast a speed, the car will understeer. It simply won't manage to complete the transient and turn into the corner in time.
2. Coarse Steering: Steering more sharply and ubruptly increases the understeer tendency. In cars with passive rear steering, the car's back end might feel as if it "swings" aside for a moment and tuck you into the corner, but this will not develope into an actual oversteer unless you slow down or brake.
3. Excessive Braking: Braking shifts the weight forward and gives the front more grip to reduce the understeer, but without feel, strong braking will reduce the grip because the front wheels use all too much of their overall grip "budget" for braking instead of cornering. Under very strong braking, the car's wheels will lockup and the car will not turn.
4. Excessive Acceleration: Understeer caused due to insensitive acceleration in the corner. The acceleration will shift weight off of the front wheels and induce understeer. In a front-wheel drive, some of the cornering force will also be used for acceleration, further reducing grip.
Oversteer is caused by:
1. Excessive deceleration: Slowing down shifts weight forward, leading to a light rear which can slide. At the extreme it can be seen as the back end of the car rendered airborne and swinging aside. Of course deceleration can also reduce front end grip, as it be used to brake instead of turning, leading to understeer, but this usually occurs under much stronger a deceleration, or such that occurs mid-corner. The required deceleration for oversteer can be achieved by going off of the gas, braking lightly, jerking the car from side to side, or steering sharply when off-throttle.
Coarse steering makes the car experience an initial understeer which transitions into oversteer because the front wheels generate more friction with the road. Likewise, jerking off of the gas will produce sharper of an oversteer than when easing off of it gradually. Another thing that can help decelerate the car is the handbrake. In most cars, it actuates only the brakes on the rear wheels, so you slow down the car and overload the rear wheels with braking forces simultanously.
2. Excessive Acceleration: Acceleration leads to more speed and less front downforce, thus creating understeer. But, in a rear-wheel drive car, the engine force loads the rear wheels with a force of acceleration. In highly strong acceleration, powerfull rear or all-wheel drive cars (as well as on slippery surfaces) the car might experience "power oversteer."
Neutral handling occurs when the driver enters a corner at just the right speed with a slight braking force. Any speed over this one will result in understeer and any speed below it will create oversteer. At any point, there is such a thing as "understeer transient." Before you can be turning, you have to turn-in. Turn-in is defined as the whole area of the corner from where the wheel is straight to just after you finished turning the wheel into the corner. During this stage the car is said to be changing directions and yawing into the corner.
The importance of this stage is that it is always defined as understeer. In other words, the car cannot experience oversteer or neutral handling before you finished turning the wheel into the corner. Some drivers try to induce oversteer by the methods above and fail just because of timing: The pull the handbrake before turning the wheel, as an example. The oversteer will be most powerfull when the provocatice action of jerking off of the gas/braking/handbrake and alike is aligned directly with the point where you finish turning into the corner, a mere fraction of a second just after the wheel is fully turned into the corner.
Prevention of Skids
Step one, don't trust the electronics. I wrote an article in the past where I explained roughly where the limitations of stability control systems lay. It's not that they are inefficient, they are highly effective. In fact, maybe that article stressed the limitations of ESP too much as to give a reliable picture of it's abilities, but it does not change the fact that it is your job to ensure the car does not slide. Remember, stability control straightens the car out of the slide, once it has occured (and lasted for a few tenths of seconds), but you can prevent the slide altoghther.
The next step is to maintain the car: Fit it with four identical tires, inflate them regularly and replace them whenever they are even moderately aged or worn. Replace old dampers to keep the car's suspension working properly. These moves will increase the grip levels and allow the car to remain further from the point of breaking away.
But the most important step is to adjust the speed to the conditions. If you remember the formal expression for the critical cornering grip, you remember than it changes upon variants of coefficient of friction, gravity, cornering radius and speed. The road surface, load in the car, suspension and tires change the coefficient of friction. The exact location on the earth changes the variation of gravity slightly, and the cornering radius depends on the corner and the line you take through it.
However, speed changes the cornering force much more dramatically than any of the above, since the velocity variant is changed by the square root. Also, as speed increases, the tires are made to operate in larger slip angles, which change the steering angles and tighten the radius of the corner. Speed can also effect the coefficient of friction on wet surfaces or when it makes tires generate heat. Overall, a slower corner entry speed is the first move to ensure cornering without sliding. Remember the "Slow in, Fast out" rule.
With that being said, managing the following steps can increase the "reserve" by 30% to twice as before. Other than maintaining the corner, proper loading is also important. The loaded axle should have less grip, but once the tire pressure is increased to match the added load, the effects cancel each other out and to a certain extent the grip levels will increase. However, the car will brake less effectivelly and have more transient understeer (take longer to react to the steering). Anyhow, try to put any additional load as securedly as possible and as low as possible inside the car, and distributed equally left to right. It's also best to try and put the cargo between the front and rear axles rather than on the car's extremities.
Choosing the right line also helps monitor the cornering radius. Taking a wide cornering line, as they are described in earlier articles, helps increase the cornering radius to increase grip levels in the corner or coming out of it.
Smoothness and accuracy also form a hugh shift in the ability to corner without sliding. Some drivers exaggerate, and can be seen steering very slowely, especially in slippery conditions. You need to maintain a gradual but decisive steering input. The more tight is the corner, the slower is the approach and the more quickely can the steering be applied and still produce a smooth result. Some cornes require a line where you must steering sharply coming into them, slightly compromising the smoothness of turning in for the sake of better vision through it.
Next comes mananging the weight transfers, which we managed earlier. Brake before the corner, and enter the bend with the brakes so the weight is biased forward. Once you finished turning the wheel into the corner, keep the car on constant throttle (in a constant speed) and accelerate out as you straighten the steering. However, if you brake into the corner or accelerate out it without smoothness and accuracy, you will reduce the grip rather than increase it. Too much braking loads the front wheels with a braking force which "eats up" grip that could otherwsie be used to steer. Acceleration out of the corner should also be as slight as possible.
The next stage is to get to know the car. Some cars have a heavy front-end where the engine is situated in front of the front axle. As a rule of thumb, these cars will experience greater understeer and require the driver to follow the above instructions much more dogmatically. Other cars have slightly softer suspensions and a more balanced weight distribution. These cars are more controlled over a larger envelope of performance, and can be driven slightly more decisivelly with a bit less smoothness than the former. Getting to know the car also referrs to the limts: Knowing when you car is likely to understeer or oversteer and how sharply.
For instance, if I drive a Peugeot 206 I know that the car is very nicely balanced and can be provoked into an oversteer under relatively light braking in the corner when near the limit, or even just by "decisivelly" lifting off of the gas. I also know that it breaks away more gradually and controlably, and allows to "play" along the corner by moving the weight forward and back to induce oversteer and understeer at will.
Reading the road surface is another skill for avoiding skids. One of the most acute causes of slides is a sudden change of the grip levels. This can be caused by thing, see through layer of ice left on a certain part of the road (usually under the shade), so called "black ice", as well as by occasional big slips of oils on the road. Potholes and glass shards can also lead to similar results. The solution begins by looking up to the furthest possible distance ahead. At this distance, you need to recognise any change of the road surface. Ice can be seen by it's shine, and oil can be seen as a range of greasy colors.
When you get over such a low grip area, the front wheels are the first to contact it and slide. But a front-wheel slide (understeer) is self solving so it doesn't last. But once the rear wheels get over the slippery substance they break away and an oversteer is likely to happen, especially when the front wheels leave the slippery area and grip again. The solution is to detect this slippery area is the distance. At this point you need to slow down as much as possible, considering the available distance and the traffic behind you and try to get around it. If you can't get around it, try stopping before it. If not possible, drive over it at the lowest possible speed, the straightest possible line and on constant throttle. Rear wheel drive cars are best declutched or flicked into neutral.
Getting a Feel for the slide
The key point of recovering from slides, other than the actual recovery input, is to apply it at the right time and in the right amount. Knowing the foundementals of car dynamics (as they are described above) and knowing your own car in particular, helps to anticipate how the car is likely to slide: If I brake through a corner in the car I described above I'm likely to recieve oversteer. If I am on constant throttle I will recieve slight understeer in any case. If there is a slight downhill incline, I will not only have less grip, but also a greater tendency towards oversteer.
The second stage is to acquire a feel for slides. If you feel the slide, you can know it's coming and apply a correction before you actually see it. This allows to react more quickely and recover before the slide develops into an actual drama. I stated before that understeer is considered safer as it can be felt through the steering. And indeed, understeer can be felt as light and "numb" steering. Good steering feel and a good grip of the wheel allows to identify this more quickely. Under power, many front-wheel drive cars actually suffer from stiff steering, due to so-called "torque steer" where the power can be felt as pressure that makes the wheel want to straighten up.
Oversteer is more misleading in this way. It can be felt through the buttocks by seating properly, mainly by placing your buttocks as snuggly into the corner of the seat as possible and using your left foot to apply pressure against the footrest. It also has a steering feel, albeit a treacherous one: The oversteer makes the rear end slide. This creates a moment where the front wheels are no longer experiencing any side force, and than they start developing a side force in the other direction, which can again be felt as pressure on the wheel, which tries to make it rotate all the way in the other direction.
Sight also helps. By looking into the corner and beyond it, as far ahead as possible, we can notice any slight changes more rapidly. If you are looking five feet ahead and the car slides aside, you will not notice it as much. But, if you are looking 400 feet ahead, once the car starts to slide off very slightly, your point of focus is shifted much more dramatically. Once this is felt, it is important to keep on using your vision. Most drivers look at what they try to avoid and steer away from it. This breeds panic and panic input by trying to steer away from the obstacle, while having little of an idea as to how much to steer. However, if you look in the direction you want to go to and steer towards where you do want to go, you will know to gauge the right amount of steering to get you out.
Another note: Cars can oversteer (or be made to oversteer) in one of two ways: The first can be felt as a subtle, gradual breakway of a tail, where the car's back end seems to gradually drift aside. This is far more controlable and desired in drifting cars and in general. The second case is when the car breaks away violently and suddenly, which is often not controlled at all. In any case, the mistake when recovering from oversteer is that drivers let the oversteer rotate them into the corner and than correct it. Do not. Once the oversteer is felt, apply a corrective input and THAN work on getting out of the corner.
Recovering from Slides
Only after you learned how to avoid a slide and how to know and feel when it is going to happen, you are ready to learn how to recover from it. This requires a lot of skill, such skill which cannot be acquired by training by yourself or by a short skidpad tuition, but let's leave the subject of training for later and touch the actual means of recovery.
A car does not skid if the driver does not do something that makes it to. So, if the skid occured, the driver did something to cause it. So, in order to recover, he needs to do the opposite, simple. I'll tell you (as you should already know) what doesn't cause a slide: the mere action of turning into the corner. There is always something else: excessive speed, uprupt steering input, excessive braking or acceleration, etc. So, the correction of the slide is never going to be to simply steer out of it. If the slide is caused by excessive speed (which always means understeer) than the solution is to wipe off that speed. If the slide is caused by excessive braking, the solution is to remove this excess braking. Of course you also need to steer the car towards the right direction, but this is done automatically by your eyes if you only look towards the right direction (as I noted above).
In case of understeer, you need to reduce the speed and put more downforce on the front wheels. So, back somewhat off of the pressure on the gas. If you must let up the throttle all toghether, be gentle or otherwise you will create a "spike" of engine braking which will make it snap into an oversteer. Sometimes you will also need to brake with feel: Enough braking to put more load on the front and shake off excess speed, but not too much as to overload the front wheels with braking forces or locking them.
The solution seems very natural for a slide: The car starts ploughing, you let go of the gas and brake with feel and you recover. It is important, though, to practice easing the gas progressively enough (exactly how progressively depends on the corner and car) and braking with enough feel to get out of the understeer as quickly as possible. There is another thing to practice and that is the steering. Like I said, steering out of the understeer is not going to work and yet most people will simply turn the wheel tighter and tighter into the corner.
When the car turns the wheels develop a slip angle between the direction the wheels are turned and their actual path of rolling. When the car starts understeering it means that the front slip angle is too large. If you steer more, the tires are still sliding in the same direction, but turned ever more sharply, so the slip angle is bigger. It's like the model of the friction circle: You just load the sliding tire with extra demands and hence increase the understeer.
It's not that it can't work. In fact, it might work in most cases. Understeer is self-solving, so increasing it makes the front tires slow down even more and the car will eventually regain grip. The problem is that this is a much less efficient method of recovery, it requires extra space which isn't normally available on the road. Also, the recover is not going to be as smooth and linear. The car will slide harder, untill eventually tighten the line back up at once, and possibly transition sharply into an oversteer at the least preferable time.
The actual solution is actually to reduce the steering angle slightly. There is a certain angle (say, 6 degrees) between where the car is sliding to and where the front wheels are pointing towards. If you reduce the steering angle (say, by 2 degrees) than the car doesn't need to tighten the line by just as much (by four degrees instead of six). Once the car has gained grip again you can tighten up the extra amplitude more quickely and smoothly.
The problem is to have the discpline to slightly reduce the steering input instead of tightening it up. In order to do this you don't only need to look in the right direction, you also need to apply the recovery input very quickely, before the car actually starts to take a wider line that forces you turn more tightly. You need to feel the slide and anticipate it, and than ease off of the gas and brake with feel while slightly retracting the steering lock. The steering should than regain it's normal feel and be "heavier", at which point you need to gently turn the wheel back to the required angle.
Oversteer is more complex. The natural response is again to brake, but this shifts more weight forward and off of the sliding rear wheels. Another natural respone is again to steer out of it by turning the wheel against the direction of the corner. This would be efficient if the cause of the slide was that you steered in the wrong way or too much, but oversteer does not occur because you over-steer, it is a result of a forward weight transfer or excessive torque in the rear wheels (in a powerfull rear-wheel drive car). The solution is to reduce those factors.
If the cause is a forward weight transfer, than we need to transfer it back onto the rear wheels, so we actually need to accelerate (not a very natural response when the car is sliding) which will pull the car forward and back to straight. This is particularly efficient in front-wheel driven cars, where we can harness the power of the engine purely to transfer weight to the rear and regain grip in the back. So you accelerate forward and reduce the steering input (or straighten it completly) and get the car to grip again. In a rear-wheel driven car, you can't use the engine's power as much, so you need to keep the car on constant throttle (just like you should do mid-corner) and steering agains the corner. Eventually the car will "take a set" and than you will make a second steering move and straighten the steering again.
The latter manner of correction is also effective when the slide occurs under excessive power (which can only happen in rear-wheel driven cars anyway). So you need to counter-steer towards the direction you want to go to (which is against the corner) while keeping the car on constant throttle and than straighten the steering back. By keeping the car on constant throttle you keep the weight of the car balanced, but without putting torque through the rear wheels. If you accelerate or decelerate you will recieve a non-linear steering response. The car will take longer to react to the steering, and than it will react all too sharply and spin you around in the other direction.
Based on the effect of resonance, the slide in the other direction is normally going to be much stronger and more dangerous than the first. The car is not likely to have any run-off area towards the outside radius of the corner, making it immediately move into the way of oncoming traffic or off of the road. The slide itself will be much more potent and often impossible to recover from. Besides, you have just steered the car sharply in one direction, only to be forced to undo the steering and turn it ever more sharply towards the other direction, all within a much reduced time spawn than before.
This is also why countersteering in front-wheel driven cars is best avoided. If you react quickely enough, or within a reasonable time spawn, you shouldn't have to countersteer. In powerfull cars, especially in sharp corners or on slippery surfaces, you can hold the wheel straight and accelerate hard enough to spin the front wheels which will push them back on the right line without countersteering. If you do need to countersteer, you again need to keep the car on constant throttle, but this is best avoided.
The exception is when the car is aquaplaning over a deep film of water or sliding over very polished ice. These situations create very little grip, as you can experience on epoxy skidpads too. In these conditions, trying to use weight transfer is not going to be effective. So there is another solution: You brake before the corner, apply constant throttle before the corner and all the way through it untill after you are perfectly straight and stable after the corner. If the car slides, you apply the clutch and steer out of it. If you try to accelerate out of the oversteer, you will spin the front wheels too much and lose front traction too. If you try to brake out of an understeer, you will lock the front wheels and the understeer will prevail.
Be declutching you allow the wheels to rotate freely and return to normal rolling motion and get over the slide. This is highly inefficient on most surfaces, only to be used when no practical grip is not existent. On these surfaces, emergency braking without ABS is to be done by pumping the brakes, unlike on any other situation.
Another situation where you need to go not following the book, is when you are not skilled enough or when the slide is beyond your control. The solution here is simple: Brake as hard as possible, as early as possible. After pressing the brake, press the clutch, if possible, and straighten the steering. This can help to stop you or reduce speed to a point where you might be able to recover from later.
Training Car Control
You can't teach yourself how to control a car in it's limits. You will want to do X, but you will do Y and think you did Z, where actually you would need to think and do something completely else. If you do get it right, you will not achieve the necessary control you will with some sort of training. Almost all activities which are considered a competitive sport requires a trainer. There are several ways of teaching car control:
The first method is a skidpad. The skidpad is made by applying a seal of epoxy onto a bitumen surface. Once soaked with water, the epoxy offers grip levels which are extra ordinarily low. The car transitions at once from full grip, higher than typically possible on the road, to a state of full blown sliding when you go onto the surface is which likely to be more slippery than any snow or grease you will tackle in a lifetime of driving. The correction input is also different (by applying the clutch) and the car is likely to illustrate a highly different handling characteristics. Some skidpads I've seen even use a plate that throws the car's rear wheels aside. Not very realistic.
A better method of training is called the SkidCar. This is a surprisingly sophisticated piece of engineering, formed as a cradle with four wheels that are allowed to run indepently, as they are installed over a car. The "cradle" is hydraulic and can, by the command of the instructor, who is sitting inside of it with a control, lift it's front or rear somewhat, and elevate the front or rear of the car, simulating reduced grip and imitating a wide range of road surfaces: Dry, wet, greasy, sand, snow, ice. The result is physically identical to the "real deal" and the modern devices don't intefere with the functions of the car's suspension.
This allows to practice all of the things we said above: You can just drive it around, and work on avoiding the slides, identifying them once they occur and controling them at that point. You acquire a feel for the slides through the steering and chassis, and control the slides. It is important, though, to practice a wide range of cars, including front-wheel driven, rear-wheel driven, all-wheel drive and cars with different weight distribution and a different suspension design.
The practice needs be further polished by doing some of it in the trainee's own road car, on tarmac, tight gravel and ice. These conditions allow to experience all of the ranges of grip, and a more progressive and sharp handling, while getting to know your own car: The driving style it likes, the cases where it slides and how it slides, and with what perliminary "warnings." Of course your tires won't like the part done on tarmac.
This whole ordeal should take at least two tuitions over two days, and it requires all skills of proper seating, steering and use of vision need to be in place before it, to reach a sufficient level of skill, which by itself needs to be maintained by a short practice once every few months at least, and an occasional practice with a trainer. Still, it's not super human to achieve a sufficient skill, and it's something that can help increase the safety of the driver, even with stability control systems.
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