The art and science of curves and cornering

I used to think that driving was basically two things: Pressing the gas pedal, and steering. Just keep the pedal down to the ground, turn the wheel where you want the car to go, and it will go there.

Later on, I, like any other person who eventually starts actually driving, learned that driving is almost an art form in its delicate balance of numerous factors. Among the most important lessons I learned (and also one of the first) was that you need to slow down for a curve. This should seem like an obvious fact, but when I was a kid I thought cars were well-engineered enough that their steering would make them turn whichever way you wanted them to face. Of course, the reality is not so, especially when you're travelling at high speed. There is no car in the world, not even the fanciest or most expensive luxury or sports car that can go around a 90-degree turn at 200 miles per hour. The laws of physics will see to it that any attempts to do so will fail. And so it follows that you must slow down to an appropriate speed when you are going through a turn.

But what is an appropriate speed? And when exactly should you start braking? This is what makes the art-form part. The answer is different for every car, and it is dependant upon the shape of the curve in the road as well. A perfectly-driven curve or turn requires that the tires not break traction (i.e. skid) at any point. This means that you cannot brake too late nor turn the car too hard. In many cases, however, braking is not necessary; Perhaps just easing up on the gas pedal will give your car enough grip at the front. Your speed is obviously a factor here, but there is another benefit to this. It has to do with a fundamental property of acceleration: It moves your car's weight to the rear.

When you start speeding up in a car, it tends to lift the front wheels off the ground. This tendency is more pronounced in rear-wheel-drive (RWD) cars, but FWD cars do it too. The result is that you lose some steering ability, because the front wheels "skitter" across the road rather than gripping it firmly. This is not noticeable in normal acceleration during everyday driving, but doing a sudden start in a sports car will produce a noticeable loss of steering control. As long as you keep the engine powering the wheels, your steering control is reduced. If you stop pressing the gas pedal, your front wheels will suddenly gain some grip and your steering will be more responsive (although you may not notice it in a typical car). Even more pronounced, however, is the tendency of the car to shift much of its weight to the front wheels while braking. As the car starts leaning forward, pressing the front wheels down into the pavement, a sudden, strong increase in steering sensitivity exists.

Another important factor in turning is how you approach the turn. This is mainly concerned with where you place the apex of your turn. The apex is, simply defined, the point where you car is closest to the inside of the turn. The "inside" of a curve or turn is the side you're turning toward. When you turn left, the left side of the road is the inside of the turn; When you turn right, the right side of the road is the inside of the turn. Conventional wisdom usually maintains that a car should make an early apex when turning; That is, it should stay close to the inside of the turn when beginning the turn. This just makes more sense, since the car will have more leeway to "drift" to the outside of the turn; The g-forces always pull the car toward the outside of any turn. (Note, incidentally, that this has a similar effect on your right and left wheels to the effect accelerating and braking have on your front and rear wheels. When turning left, the weight of the car is shifted to the right side; When turning right, the weight of the car is shifted to the left side. If you are braking in a left turn, your right-front wheel is the "heaviest" wheel in the car. To put it another way, your right-front wheel is the most "loaded".) In a gentle curve, early apexing is usually the best driving practice.

However, there are times when making a late apex is called for. Imagine a car which is driving along (parallel to) a brick wall. At some point, a gap appears in the wall which the car wants to drive through. If the car is close to the wall and the gap isn't much wider than the car itself, will the car be able to turn directly into the gap? Chances are, it won't. It would need to pull a 90-degree turn in a very short space. Going through such a gap would require making a late apex, which would involve actually turning the car away from the wall, putting some space between the two, so the car would have more room to make its turn. This is a late apex because the car begins with being far away from the inside of the turn, and is closest to the inside when the turn is finishing. Late apexing is absolutely necessary for making some tight turns; It is commonly seen in parking lots, for example. If you have a parking spot coming up on your right, do you prepare to turn into it by staying close to the parked cars on your right? No, because then you wouldn't be able to turn directly into the space. Instead, you actually steer your car to the left before you reach the parking space, so you'll have more room to turn yourself around to the right, making for a more straight-in approach. Just as knowing where to slow down and how much to slow down is something that must be developed by "feel", so is knowing where to apex in your turns.

Your car's suspension configuration has a pronounced effect on how your car turns around. If you thought suspension was to make the car feel more comfortable... Well, you're right, but it makes the car handle a lot better, too. Imagine a car which had no springs or shocks, but simply fixed wheels which went up and down with the car's body. Every time the car hit a small bump, the wheel going over the bump would rise in the air. It would not be effective at providing traction, because a tire needs to be pressing against the ground to give traction. An airborne tire is useless. Suspension helps to keep the wheels on the ground by pressing them downward. The car's body is free to go up, but if it does, the suspension will press the wheel down, helping to keep it against the pavement. But not all suspension is the same. There are two main factors that characterize the performance of suspension: Stiffness and speed.

Stiffness is, obviously, the resistance of the spring or shock to compression. A stiffer spring will tend to retain its shape, while a soft spring can be more easily pressed together. Some stiffness is obviously necessary in suspension to keep the car from dragging on the ground, but if it is too stiff, it has the effect of having no suspension at all: The springs will not let the wheels ride with the road, but they will simply bounce above the road. Generally speaking, a softer suspension will give the wheels more grip, because it will keep them on the road more, while a stiffer suspension will make the wheels more prone to losing their traction.

In the real world, this is a delicate balancing act. If you could see a continuous readout of the loading of your car's wheels, you would probably be amazed at the volatile nature of the weight on your car. Your car's mass is constantly shifting in response to its movements, putting weight variously on the different wheels as you speed up, slow down, and turn. It is important, therefore, to not only make the suspension of the right stiffness, but also to distribute this stiffness evenly. A car with a very stiff front suspension and a very soft rear suspension, for example, will have a hard time steering. The front wheels will shift unsteadily over the road, resulting in some lack of control. This is called understeer, for obvious reasons: You don't have enough steering control. (Understeer is commonly known as "push".) On the other hand, a car with a too-stiff rear suspension will oversteer, and it may tend to "fishtail", which is exactly what it sounds like: The rear end will be loose, sliding from side to side like the tail of a swimming fish. It will tend to slide toward the outside of a turn, and as anyone who's ever experienced it can tell you, driving a car in which your rear end has suddenly broken traction and is sliding out from under you is not a pleasant feeling. This leads to the necessity of balancing the suspension, keeping the front and rear in tune with each other, while maintaining enough downward force on the wheels (with opposite upward force on the rest of the car) to keep the car body from scraping against the ground.

The other main factor in your suspension's performance is speed, that is, how quickly it decompresses. When you compress a car's suspension, it bounces back fairly quickly, but it doesn't happen instantly, and when a car is moving at driving speed, fast response time is important. This comes back, once again, to keeping the wheels on the ground: If the suspension does not decompress quickly, the wheel will not get pushed into the ground, but will "float" in the air for a while. And as we've already mentioned, a tire that's in the air isn't doing anything. A too-slow suspension can result in loss of control because your wheels aren't returning to the road. On the other hand, a too-fast suspension has much the same effect as a too-stiff suspension. Springs and shocks tend to get slower with age, as well; A worn shock will not return to its original shape as quickly as it used to. This is why keeping your suspension in tune isn't just a matter of comfort; It's also safer.

Another interesting factor affecting your car's grip on the road is its aerodynamics, which of course is how air flows over the car. Unlike the suspension, which can be too much one way or too much the other way, aerodynamics usually work by a very simple formula: The more downforce your car has, the better it will handle and the slower it will go. The more surface your car presents to the relative wind (the wind-like air pushing against the car as it moves), the more that relative wind will push the car down towards the ground, giving you a better grip. This will slow your car down because of the air pushing against it, but it means a more stable, controllable car. This sometimes leads people to go to extremes in their car's body shape, putting spoilers of ridiculously large size to try and make their cars more sporty. This is certainly giving them a lot of downforce, but it kind of defeats the purpose of having a fast car in the first place.

The other main car configuration that affects your car's handling is the alignment. This refers to how the wheels are positioned relative to the body of the car. There are two main factors in your alignment: Toe-in, and camber.

Toe-in is the turning of the wheels inward or outward. Toe-in is said to be positive when the wheels are "pigeon-toed", with the front ends pointing inward, and negative when the front of the wheels are pointing outward. A positive toe-in on the front wheels will make the car more responsive to steering, but it also lessens the car's stability, and the front of the car may shudder from side to side during braking. Negative toe-in at the front tends to create understeer, but makes the car more stable. The rear wheels should, as a general rule, always have negative toe-in, or severe oversteer is quickly created.

The camber of the wheels refers to their vertical tilt. If the wheels are leaning outward, so that the tops of the wheels are farther from the car than the bottoms, this is positive camber. If the wheels are leaning inward, so that the tops are closer than the bottoms, this is negative camber. Even to a non-mechanic, it should be clear that negative camber is a better idea, because positive camber makes the car tipsy, while negative camber gives it a solid, stable platform to rest on.

Of course, all these adjustments to the alignment are very small. The human eye, unaided, cannot tell if a car has negative or positive toe-in or camber; A mechanic uses specialized tools to measure and adjust these settings with minute precision. So don't try to start beefing up your car by making these adjustments yourself, or you'll probably find your car to be undrivable.

I didn't care much for driving several years ago; It just seemed like such a mindless pursuit to me. But when you start to learn about the finer points of driving, and how much of a tightrope walk it really is, you start to realize that it actually takes a lot of skill and experience from the driver. It's said that real drivers are made during turns. After all, anybody can drive a car in a straight line; That takes no skill (or at least, much less). It's relatively easy to keep a car on the road when you're going straight and the state of the car is stable and unchanging. When you start to appreciate the factors that affect how a car goes through its transition phases, you'll not only find driving a more interesting phenomenon, you just might be a better driver as well.

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