Бесплатный фрагмент - Extreme and defensive driving

Introduction

Extreme and defensive driving — are strongly coupled driving styles, covering body of knowledge about cars, its components and parts and how it works, driving experience and skills. Extreme driving means driving a car at its limit of potential and learning basics sports elements (high-speed cornering, drifting, braking methods, study of special terminology and so on) to achieve a minimum lap time. Defensive driving is focused on preventing crashes related to a partial loss of control over car (for example, when the front wheels lose grip with the road in a corner).

Control a racing car is a mastery that takes years to master. Handling a sport car by a professional racer is comparable to virtuoso playing of a musician on the guitar or piano. You ask: “Why do we need extreme and defensive driving skills, when we are either driving calmly in a straight line or standing in a city traffic jam?” The answer is simple: no one is immune to accidents on the road that can occur no matter what your driving style is. If a driver does not have the necessary skills, defensive driving techniques are not worked out and are not brought to automatism — the driver can count on luck only.

Content of the book is divided into two parts: “defensive driving” and “extreme driving”. The material is built by an education course and is not difficult to master by a person, who has basic skills of driving car and is familiar with how it works. The content includes:

• tests results, their analysis and generalization;

• descriptions of operation of car components, that affect behavior of car and control techniques;

• the techniques and methods of extreme and defensive driving;

• requirements for successful completion of the driving techniques;

• description of the driving techniques in circuit racing;

• a set of exercises for self-training of drivers and racers.

The book is not a collection of postulates and canons, but is a help in mastering driving skills. The author is not responsible for road traffic accidents, related to a lack of understanding of operation of car components, the driving techniques and their incorrect doing, with inappropriate technical characteristics of cars and accidents caused by non-compliance with precautions when performing the exercises. All techniques should be performed after preliminary tests on the car and careful training of the driver. The responsibility for driving lies entirely with the driver.

DEFENSIVE DRIVING

First part of the book is independent and is mainly aimed at mastering of defensive techniques. To bring the techniques to automatism, at the ends of the chapters exercises and tests are offered that simulate situations that may arise on the road. In the text of the first part of the book there are practical parts “test” for testing car and the defensive techniques and “requirements” for successful completion of the defensive techniques. Driving techniques are shown in the form of flowcharts and marked with the letter M.

Front wheels sliding

The phenomenon when car not answers steering wheel turns, moves along straight trajectory (or trajectory begins to straighten) due to loss of grip of the front wheels on the road, is called understeer. Car shows understeer (low steerability), when the front wheels slide on the road.

The figure shows, how we entered a corner at a fairly high speed and pressed the brake pedal to the stop, which caused the front wheels to lock and, as a result, front wheels sliding.

Consider what happens with a contact patch of the front tyres to the road when understeer due to heavy braking.

The figure schematically shows deformation of a tyre during front wheels sliding, when the front wheels are turned by the steering wheel at a large angle. Contact patch is marked gray. When braking, load on the front axle increases, so contact patch also increases. When understeer, the tyre deforming, contact patch rotates to direction of movement, and so-called tyre slip occurs. Tyre slip is angle of twisting of contact patch relative to direction of movement of the wheel. Steerability factor is defined as ratio of rear wheels contact patch to front wheels contact patch. If front tyres deformation exceeds rear tyres deformation, steerability factor is less than one. In this case, they say understeer or low steerability.

Sliding of the front axle is reflected in feedback of the steering wheel. If at entry to a corner, the steering wheel turned with some effort, and after car stopped obeying the steering wheel and the steering wheel began to rotate more easily, then sliding of the front wheels began. After the front wheels regain traction, feedback of the steering wheel is also restored.

Sliding of the front wheels is a cause of accidents. Let us list causes of understeer, which are related to driver errors:

• too high speed or large angle of turn of the front wheels on entry to corner;

• excessive braking during cornering (including wheels lock).

Common mistake: a driver over speeds at entry to a corner and, fearing that trajectory would not fit into borders of the corner, turned the steering wheel deeper into the corner and pressed the brake pedal. If the front wheels are turned too much, they slide on the road. After pressing the brake pedal, the front wheels lock. In the end, trajectory becomes straight, car go out of the corner or collides with a barrier.

When entering a corner at high speed you may feel that trajectory will not able be laid within the corner. When it seems that we do not fit into a corner — it is important not to lose your composure. In no case you should sharply hit the brakes and continue to turn the steering wheel in direction of the corner, as these actions will only worsen the situation, there will be sliding of the front wheels. It is necessary to depress the throttle pedal and start to slow down smoothly in the corner. Let us consider examples of trajectories of passing through a corner.

1 — is “ideal” trajectory of sports style cornering, 2 — entrance to the corner was a high speed, 3 — speed on the corner entry was so high that no chance to avoid way out of the corner.

While driving along trajectory 2, speed of car gradually decreased with help of soft braking. Note that radius of trajectory 2 gradually decreases, as with smooth braking speed of car gradually decreases. It can also be seen that when driving along trajectory 2, car moves along outer edge of the road, unlike trajectory 1. If the front wheels began to slide, trajectory 2 would straighten out and not fit into the corner. If at entry to a corner it is found that initial radius of trajectory is too large, this does not means that it will not be possible to lay trajectory within the corner.

What can be methods of dealing with front wheels sliding, if it still occurred?

1. If sliding is caused by braking, the first step is to depress the brake pedal. This should put control back in our hands.

After the wheels have regained their grip on the road, you need to start soft braking if you need to slow down.

2. If the steering wheel is turned at a too large angle, straighten it to restore grip of the front wheels on the road. Speed of car, grip of the tyres on the road, turn angle of the wheels are interrelated parameters. There is no point to turn the steering wheel at too large angle if car is not able to move along trajectory of desired radius: instead of small radius we get sliding of the front wheels and straightening trajectory of movement.

3. Drifting is controlled process, unlike sliding of the front wheels. Therefore, it is possible to stop sliding of the front wheels by drift. By causing the rear wheels to slide, we regain control of car. In addition, speed of vehicle will fall during side sliding. There are various ways to cause the rear axle to slide. Let us look some of them.

a) Sliding of the rear axle can be triggered by using the handbrake. After sliding occurs, you need to turn the steering wheel against of drift direction (against of direction of car rotation), so that car does not turn around. After speed of movement drops, we restore trajectory.

b) A small slide of the front axle that occurs at exit of a corner can be extinguished by sharply pressing of the throttle pedal (this is used for a rear-wheel drive car only, sufficiently high engine torque is required).

To eliminate understeer at exit of the corner, we sharply pressed the throttle pedal. When the rear axle start drifting, we had to depress throttle pedal and turn the front wheels to the left to stop increase of the drift. After that movement speed decreased.

c) Drifting of the rear wheels on rear-wheel drive car can be caused by following method: press the clutch pedal, press the throttle pedal and gain high engine speed, then depress the clutch pedal without depressing the throttle pedal. After that, if engine torque is enough and it is sufficiently inert, the rear wheels should start slipping and the rear axle begin drifting. This technique can be used if there is shortage of engine torque or time to perform reception b).

Jerk traction created by a method b) -c) will cause drift of the rear axle, slightly speeding up car. After drift occurs, you may depress the throttle pedal and try to stabilize car, winning distance from edge of the road. It should be borne in mind that drift of the rear axle is no less dangerous than slide of the front axle. Therefore, you need to apply all the techniques consciously, after training and careful preparation.

During cornering there is a roll of body and the wheels on outside of corner are loaded with mass of car, and on inside, on the contrary, they are unloaded.

Hereafter for brevity wheels, on which vertical load increases, we will call loaded, and wheels vertical load on which decreases — unloaded. When wheel is loaded, its grip on the road (friction force) increases, and when wheel is unloaded, its grip decreases.

Important note: limited slip differential may be required to cause rear axle drift due to the engine torque. To provoke drift, the engine torque must be transferred to both loaded and unloaded wheels, which can be only by limited slip differential. If motor has low torque and differential has no internal friction, there may be difficulties in creating drift.

Consider the demonstration of understeer on example of emergency maneuvering, this is relevant for city conditions. Let us say that obstacle has appeared in our path while we are moving. Our task is to avoid obstacle and come to the stop without incident. To simulate such situation, we will use a test in the form of special markings and placed cones on the test ground.

Along the strip of cones we will accelerate the car. After we achieve fixed speed (in this case, we will gain speed of 75 km/h), we will move strictly straight along the strip of cones to the vertical marking, without taking any action. As soon as we achieve the line, our hands will be untied, we will be able to perform any actions with the controls. Shaded area — is an area where may be obstacles. Hitting the shaded area or turn the car around will be considered as a failure. We need to avoid sector of expected location of obstacles and stop. Let us call this test “understeer test”.

So, the first test. We gain 75 km/h, after the line we brake, trying to go left the leftmost cone.

Pressing the brake until it stops caused the front axle to slide, and the car hit into the shaded area. If there was an obstacle, there would be collision. Aggressive braking during maneuvering is unacceptable. Now we are going to maneuver without braking. As in the previous test, we gain speed of 75 km/h and move strictly in straight line, after the marking we try to perform the maneuver.

When we achieve the line, we depressed throttle pedal and turned the steering wheel sharply to the left. The car started drift and almost turned around. This is due to our car has high steerability. Return to the starting position and repeat the test. Now we work with the steering wheel more precisely and composedly.

We successfully went around the shaded area by depressing throttle pedal and working with the steering wheel only. After bypassing the danger zone, we braked to the stop.

In this test you can select geometric parameters: distance from vertical marking to the shaded zone and its length from the center of the acceleration band.

For fixed dimensions, there is maximum speed at which car can pass the test. In this case speed was 75 km/h. At higher initial speed, the car inevitably hits into the shaded area.

Understeer and sliding of the front wheels occurs, as rule, when driving cars that have low steerability. For vehicles with low steerability, sliding of the front wheels is quite often.

Exercise 1. Provoke sliding of the front wheels by locking the wheels with heavy braking, when moving around a ring or passing a corner. Depress the brake pedal and regain control of car.

Exercise 2. Repeat previous exercise, but now press the brake pedal not to the end, a little weaker. Gradually reducing effort on the brake pedal, find optimal pedal position when the front axle does not slide and trajectory is maintained, but car reduces speed as quickly as possible.

Exercise 3. Provoke understeer by turning the steering wheel too much. Take control of car back by slide of the rear axle with handbrake.

Exercise 4 (for rear-wheel drive). Accelerate smoothly at exit of a corner to get sliding of the front wheels. Suppress understeer by causing the rear axle to drift with help of engine power. This may be sharp press on the throttle pedal or spin of engine with subsequent depressing of clutch pedal.

Exercise 5. Place cones on a ground to perform the test described in this chapter. What is maximum speed at which car can pass your test?

Exercise 6. Moving at constant speed, turn the steering wheel to find position of the front wheels, at which radius of trajectory is minimal, but the front axle does not slide.

Exercise 7. Place cones on a ground that simulate a corner. Make long distance behind the cones, ensuring safe exit from the corner. Enter corner at speed at which the front wheels slide and car go out of the corner. With help of previously practiced techniques, extinguish speed at entrance to the corner to overcome slide of the front axle.

Steerability

Steerability is one of the most important characteristics of car. In many cases behavior of the vehicle can be described by the term of steerability. Steerability — is speed of change the longitudinal direction of the body when the steering wheel is turned while driving. Steerability shows how car will behave while moving after turning the steering wheel.

Steerability may be low, neutral, or high. Steerability affects the behavior of car in corner and, as a consequence, the technique of passing corner.

Let us run a couple of tests. We will use two cars. The first is a retro car, a 1970 rear wheel drive sedan. Like many cars of those years, it has a big and heavy engine, which is located in the front. The second is a modern 2011 front wheel drive hatchback with a lighter engine, which is also located under the hood in front of the front axle. Fuel injection on the hatchback engine is carried out by injectors controlled by an electronic engine control unit. Torque of this engine is lower and shifted towards higher rate (compared to the sedan engine), but the engine develops more power at high rate.

The tests will be carried out on a single corner. We will enter the corner at over speed, at which a car does not “build in” the corner a little.

At the entry to the corner depress the throttle pedal and press the clutch pedal, after which we quickly turn the steering wheel all the way to the corner and keep the steering wheel in the full turned position. When speed drops below 10 km/h, press the brake and stop. First, we test the retro car.

After turning the steering wheel the car did not move along trajectory of desired radius. The front wheels began to slide. You can see the tyre trace of the left front wheel unloaded in the corner. Eventually, the car flew out of the corner. When trajectory is straightened, there is slide of the front axle and car cannot move along trajectory of desired radius, it is said that car shows low steerability or understeer. Car with low steerability when maneuvering is disposed to sliding of the front axle. When driving car with understeer, the body unwillingly turns after turn of the steering wheel.

Now we mount the hatchback and repeat the same experiment.

We got trajectory with smaller radius. If you compare the final positions of the bodies, the sedan body turned at angle less than the hatchback body.

In the modern car, in addition to sliding of the front axle, began drift of the rear axle, after which the car lost speed in drift and went inside the corner. This means that the car’s steerability is high. High steerability is accompanied by oversteer and sliding of the rear axle. When you turn the steering wheel the body of car with high steerability begins to turn quickly in the direction of corner, and there is drift of the rear axle.

Let us compare the characteristics of the cars. The old sedan front track is less than the rear track, the hatchback has the conversely. The sedan has engine at the front, like the hatchback, but the base is longer, which means the center of mass is moved away from the rear axle. The automobiles have different body types — sedan and hatchback. Thus, the steerability is affected by width of the front and rear tracks, mass and its spacing. Let us look at some examples.

In race cars prepared for drag racing, the front track is less than the rear, and the heavy engine is at the front, at large distance from the rear axle. All this creates desired very low steerability. Besides, on the front axle of these monsters — are very light wheels with small diameter compared to the rear. The huge wheelbase allows you to accurately adjust trajectory.

In the rally hatchbacks with front and all wheel drive are popular. The front track is usually wider than the rear. The steerability of the rally cars with these types of drive is often high.

Cars prepared for oval racing — are front engined sedans with large wheelbase and less the front track than the rear. Their steerability — is low.

In circuit racing cars with different steerability are used, depending on type of race track, driving style and preferences of racer. Beginning drivers who participate in circuit races usually prefer stable and predictable car behavior and tend to choose low steerability. High steerability allows you to enter corners faster, but driving car with high steerability requires the racer’s driving skills and special car settings.

Let us sum up the results of our tests and reasoning.

• on car with low steerability it is easier to fly out of the turn;

• hatchbacks have higher steerability than sedans;

• if the motor is distanced from the rear axle we get less steerability;

• low steerability is priority for drag and speed racing, such as oval;

• high steerability is well suited for non-speed tracks with lot of corners.

Settings that result in reduce of steerability:

• narrow of the front track and widen of the rear track;

• increase the front clearance and decrease the rear clearance;

• increase deflection rate of the front suspension springs and decrease deflection rate of the rear suspension springs;

• increase the bump and rebound resistances of the front shock absorbers and decrease the bump and rebound resistances of the rear shock absorbers;

• increase the stiffness of the front antiroll bar and decrease the stiffness of the rear antiroll bar;

• use of more hard front tyres and soft rear tyres;

• increase pressure in the front tyres and decrease pressure in the rear tyres;

• increase camber of the front wheels and decrease camber of the rear wheels;

• increased toe in of the front and rear wheels;

• increase aerodynamic downforce of the rear of car and decrease aerodynamic downforce of the front of car;

• increase side aerodynamic drag of the rear of car and decrease side aerodynamic drag of the front of car;

• move the center of mass to the front axle (distance the center of mass from the rear axle);

• decrease inertia moment (mass or diameter) of the front wheels and increase inertia moment of the rear wheels.

Opposite actions lead to increase of steerability.

Influence of the aerodynamic elements on car behavior strongly depends on speed of movement. At low movement speeds effect of the aerodynamics on behavior of car is negligible. But at high speeds, when heavy air flows, influence of the aerodynamics becomes significant.

In practice, as a rule, it is difficult to talk about neutral steering — this term exists in theory and mathematics. After tests, you can only tell what kind of steering appropriate of car — understeer or oversteer and how pronounced oversteer is. Only theoretical calculations (we are talking about so-called steerability factor), which take into account large number of variables, can accurately tell what kind of steerability car has. Oversteer can be estimated qualitatively by angle of drift or by distance between traces of the unloaded in corner wheels of the front and rear axles.

Besides drift angle, steerability can be evaluated by passing the following test.

Test of steerability. Gain certain speed, press the clutch pedal and quickly turn the steering wheel to fixed angle. After vehicle is rotated 180 degrees, determine the distance between the starting and ending positions of car.

Let us run this test on the hatchback and measure distance between initial and final trajectories.

As result the distance was slightly more than four lanes. If the greater distance obtained in the test, therefore, lower steerability. After changing vehicle settings (for example, spring rates, stiffness of antiroll bars), you can repeat the test and compare the results. Initial speed and turn angle of the front wheels must be the same. Steerability, which we have determined by methods described in this chapter, we will call steerability or steerability of coasting motion.

In the tests we turned the steering wheel against stop (angle of turn of the wheels is about 40 degrees), the front wheels slide. If you turn the front wheels at a smaller fixed angle (10—15 degrees), drift angle (steerability) will be higher, since load on the front tyres will be less.

With help of the controls, you can increase or decrease steerability. For example, if you press hard on the throttle pedal on rear wheel drive car while cornering, the rear axle can easily slides. That is pressing the throttle pedal on rear wheel drive car leads to acceleration not only, but also increases steerability. On front wheel drive car, on the contrary, pressing the throttle pedal causes car to straighten trajectory — this is effect of reducing of steerability. Oversteer (high steerability) may be created by using the handbrake: it is often possible to see drivers in rally races enter the hairpins with sliding of the rear axle, locking the rear wheels.

Steerability created with help of the controls will be “added” to the vehicle’s steerability. Let us say if car has very low steerability, it will be more difficult to send it into drift due to traction on the rear axle than car with high steerability.

Exercise. Try to determine steerability of your car. For this purpose you may place cones on ground that simulate a corner and do the test. Do not forget about safety: car can show very low steerability, or it can start slide and turn around, so there should be enough space on the ground.

Be careful! Incorrect “tuning” of car (it may be suspension parameters, track, ground clearance) can make your car unsafe. Manufacturers design passenger cars in such way that they are stable and do not roll over during sudden maneuvering. If there is a risk of overturning in a corner, turn the steering wheel against the direction of the corner to return vehicle to the four wheels.

It is worth noting that electronic drive control systems, electronic control of torque distribution on the wheels, dynamic electronic motion stabilization systems can distort perceived steerability of car.

Drift: causes of origin and methods of fighting

When the front axle slides, we lose control. Unlike understeer, drift — is a controlled sliding of car. There may be one or both axles in the slide. Tendency to drift and behavior of machine when drift are influenced by such parameters as the type of drive, steerability, the type of differential. During drift, the rear axle tends to bypass the front. For clearness, if longitudinal direction of the body deviates to the right from direction of movement, we will say that car drifts to the right (drift direction is to the right), and angle between direction of movement and longitudinal direction of the body will be called drift angle.

This rear-wheel-drive car is specially prepared for drifting. It is equipped with limited slip differential, high torque motor, negative camber of the wheels and an increased full lock angle of the front wheels. On a front-wheel-drive car it is may be easily get out of any angle of drift, if engine torque is sufficient to maintain skid of the front wheels. For example, on this car, we entered and exited drift several times one after another.

The sliding behavior of an all-wheel-drive car depends on distribution of the torque among the axles. If main part of the torque is applied to the front axle, behavior of car will be close to behavior of a front-wheel-drive car. This all-wheel-drive car feels like a front-wheel-drive car: when pressing the throttle pedal the car tends come out of drift.

But unlike front-wheel-drive, on all-wheel-drive car it is possible to maintain stable drift due to part of engine torque transmitted to the rear axle. In addition it is easier to maintain a slide on all-wheel-drive car than on rear-wheel-drive car (with an appropriate ratio of the torques transmitted by the engine to the front and rear axles), since traction on the front axle will not allow car to turn around.

It is worth noting, that when drive in reverse when turn the steering wheel the front axle can drifts. We accelerated in reverse and quickly turned the steering wheel, whereupon the car turned almost 180 degrees.

Inability to drive car in a drift often leads to accidents. Rear-wheel-drive car with usual differential (zero or low friction) is quite difficult to drive in a drift. Take for testing a rear-wheel-drive car with zero-friction differential (factory) on the rear axle. Let us look at what may be causes of occurrence and ways to provoke rear axle drift.

1. Braking by handbrake. It is the simplest and most understandable cause.

2. Aggressive throttling on a rear-wheel-drive car. Please note — with a standard differential the first starts to skid wheel from the inside of corner (the unloaded wheel).

3. Speeding of engine and depressing the clutch on a rear-wheel-drive car. If you push the clutch, gain engine speed and, without releasing the throttle, release the clutch, the rear wheels will skid.

We revved up the engine and casted off the clutch pedal. The both rear wheels began to skip, the rear axle began to drift.

4. Engine braking on a rear-wheel-drive car. When the throttle pedal is released, firstly, the front axle is loaded and the rear — is unloaded.

Because of this grip of the front tyres with the road increases, the rear — decreases. Secondly, there is a braking effort on the rear wheels caused by engine braking. These facts lead to increase of steerability and can cause drift when maneuvering on a rear-wheel-drive car, especially on a high steerability car. Soft braking with engine braking together can have the same effect. In addition, roughs on the road unload the rear axle awhile, which combined with engine braking increases risk of sliding on a rear-wheel-drive.

5. Downshift without throttle blip on a rear-wheel-drive car with a manual gearbox. After lowering the gear and releasing the clutch pedal the engine is forced to gain speed in a short time distance, which can be indicated by a jump of the tachometer needle. On rear-wheel-drive, this is equal to action of the handbrake.

6. Braking with a strong shift of brake balance to the rear axle. When balance of the braking system is shifted to the rear axle, steerability may increases during braking. It may happen that the rear wheels will be first to brake.

7. Rocking the center of mass. Rocking can cause drift when passing an S-like corner.

When direction of movement changes, the energy stored in the compressed suspension, is freed and pushes car in opposite direction, which can lead to drift.

8. Together pressing the throttle and brake pedals on a front-wheel-drive car. Moving along the ring on a front-wheel-drive car, let us press the throttle and brake pedals at one time.

There was drift of the rear axle, the car rushed inside the ring. That is, the pressed throttle and brake pedals on a front-wheel-drive car create oversteer. Since we pressed on the throttle when braking, there was traction from the engine on the front axle. The rear axle brakes more intensively than the front, not exclude the rear wheels may be locked. Braking by the rear wheels creates oversteer, which is similar to braking by the handbrake. To describe operation of the front axle we take into account the several factors:

• due to the roll in the corner the left wheels were loaded with mass of the car, and the right wheels were unloaded;

• the front wheels are affected by the engine torque and braking effort;

• the engine torque is divided between the front wheels by the differential.

On the front axle of the car a zero-friction differential is installed, which transmits half of the engine’s torque to the each wheel. To explain the test results, we assume that the engine torque is enough to maintain traction on the front wheels when the brake pedal is pressed full way down.

For demonstrativeness of illustrations we introduce the concept of equivalent force. Equivalent force is the force that must be applied to the top of wheel to obtain the torque on wheel (this may be engine torque or torque generated by a braking system).

The figure shows the force was applied to the top of the wheel and compels the wheel to rotate faster clockwise.

Let us draw equivalent forces that occurred when one time press the throttle and brake pedals in the previous test.

At the left figure black arrows indicate equivalent forces created by braking system, white arrows — equal equivalent forces corresponding to torque produced by the engine and is divided between the wheels by differential. The right figure shows the resulting equivalent forces on each front wheel, which corresponds to the resulting torque (difference between engine torque and brake system torque). We did not press the brake pedal to the end, the braking effort on rear loaded wheel was not enough to lock it.

If braking effort is high enough, the rear wheels may become locked. Let us imagine a case when the rear wheels are locked. Note the locked wheels with crosses.

Direction of the equivalent forces corresponds to direction of movement of the front wheels. Front unloaded wheel has worse grip on the road than the loaded one, and there is a chance that it starts to slip. If the unloaded wheel starts to skid, the main part of the engine’s power will be transferred to it.

Although pressing the throttle and brake pedals creates oversteer on a front-wheel-drive car, steerability may be reduced by engine’s torque. If the rear wheels are locked, but the engine has an enough high torque, car will not turn around in a drift due to high traction on the front wheels. At the same time, if braking effort on the front wheels is fully compensated by the engine torque, maximum steerability will be achieved.

Increased friction of differential allows you to transfer more torque to loaded front wheel and thus more efficiently implement engine power. Let us represent equivalent forces, when a limited slip differential is set on the front axle.

The left figure shows equivalent forces generated by braking (black arrows) and engine torque (white arrows). Figure on the right shows resulting equivalent forces on the front wheels after subtracting the braking effort from engine torque. A greater amount of torque on loaded front wheel means that more engine power will be transferred to the wheel compared to situation, when a zero-friction differential was installed.

Thus, traction on the front wheels when braking creates oversteer. Presence of a small traction on the front wheels during braking is equivalent to shifting balance of braking effort to the rear axle. But too much traction on the front wheels can lead to straightening of trajectory (understeer).

In addition to the previous reasons, drift can be caused by a sharp change in the road surface. For example, if a driver inadvertently drove a rear wheel to wayside of the road on which there is ground or snow, car can drift. An inexperienced driver, as a rule, does not operate with information about condition of the road surface and how it should affect the braking path and control technique. If you move in the “normal” tempo, familiar for dry weather, a rear-wheel-drive car can easily start drift at exit of corner on a wet road. Another danger may be invisible ice under the snow. Unsuspecting driver moving quite calmly on the road or passing a corner, can hit into emergency situation.

You can create oversteer in all the ways that you can create rear axle drift. For example, shifting the brake balance to the rear axle will increase steerability when braking at entry to a corner. On a front-wheel-drive car steerability can be improved by using the throttle and brake pedals together.

Ways to go out of drift

Front-wheel-drive

Consider ways to get out of drift. At first consider the front-wheel-drive type. We will provoke drift by the hand brake. When the rear axle begins drift, we must press the throttle pedal to 100% and direct the front wheels against direction of drift to stop the drift.

There are noticeable traces left by locked rear wheels during the action of the handbrake. The first was locked the unloaded wheel. After the end of handbrake action, the throttle pedal was pressed and the steering wheel was turned against of the drift direction. It may be seen unloaded front wheel began to grind after pressing the throttle pedal. This is explained by the fact the machine has a zero-friction differential. Before the end of the drift the steering wheel was returned to the “straight” position, after the throttle pedal was released.

The psychology of an untrained driver forces him to release the throttle pedal when a drift occurs, regardless of the drive type. This is a common error in driving a front-wheel-drive car. Finding himself in an unfamiliar situation, overcame by sense of fear, the driver releases the gas pedal. So the drift increases. Eventually, driver loses control over the car, the car continues to move by inertia, as if there is no driver in it.

For successful exit from any angle of drift on a front-wheel-drive car engine torque must be enough, to keep skidding of the front wheels at least on the first gear, otherwise the engine will fail. If drift angle of 90 degrees or more occurs it is likely, that you will have to lower the gear, to increase torque on the front wheels.

Rear-wheel-drive

On a rear-wheel-drive car the throttle pedal must be released when exiting from drift. Let us take a rear-wheel-drive understeer car. We will provoke drift of the rear axle by pressing the throttle pedal roundly when passing a corner. To stop drift, depress the throttle pedal and turn the steering wheel against of drift direction. When drift begins to decrease, we will immediately return the steering wheel to the “straight” position.

When exiting a drift with help of steering the maximum drift angle from which you can exit depends on the maximum turn of the front wheels. Note that during exit from drift, the front wheels of the car are directed along the direction of movement. If a zero-friction differential is installed on the rear axle and no friction is created inside the differential when negative load, then braking by the engine will create noticeable oversteer. Therefore, in the case of zero-friction differential, it is better to squeeze the clutch during fight with drift, to exclude engine braking.

At next, we will try an experiment. Let us see, what happens if press together the throttle and brake pedals, while the car is in a drift.

During pass the corner we provoke drift by throttling. Then we hit the throttle and brake pedals at the same time. The front wheels were locked, and there was traction from the engine retained on the rear wheels. Rear unloaded wheel began to skid. Trajectory straightened and drifting stopped. There are visible tyre traces, left by locked front wheels and unloaded rear wheel, which slipped on the asphalt.

Consider what happened to each axle when the throttle and brake pedals were pressed together. Since the drive is carried out on the rear wheels, the front wheels will only be affected by the braking effort, which causes the front wheels to lock. Locked front wheels cause understeer. Now let us look at what happens to the rear axle. For now imagine, that the rear axle has a zero-friction differential. The rear wheels will have braking efforts and equal engine torques.

The left figure shows equivalent forces, created by braking (black arrows), and equivalent forces, caused by engine torque (white arrows). At the right figure the resulting equivalent forces on the rear wheels are shown in white arrows. High braking effort on the front wheels locked them. On the rear axle a small traction was retained. As you know, traction on the rear wheels leads to loading the rear axle and unloading the front. To lock the front wheel is easier, when the front axle is less loaded. As a result, conditions for understeer are created.

The torque on the rear axle can be adjusted so that the braking effort is compensated: neither traction nor braking effort will act on the rear wheels. In this case only the front wheels will brake, which is similar to a strong shift of brake balance to the front axle. As for power, it is distributed unevenly between the wheels: zero-friction differential transfers the main part of engine power to the unloaded wheel.

At the figure the arrows show the power transmitted to the rear wheels.

The torque on unloaded rear wheel causes it to spin rapidly and skid on the road surface. When the trajectory gradually straightens and roll of the body decreases, the unloaded wheel regains grip on the road, speed of rotation gained by it decreases sharply. At that there is a push against the direction of drift, which causes the trajectory to straighten even more.

If a high-friction differential is installed on the rear axle, more engine torque will be transmitted to rear loaded wheel, than to rear unloaded wheel. When the throttle and brake pedals are pressed at the same time, there will be less understeer, than in the case of a zero-friction differential, since the increased torque on rear loaded wheel will push the car in the direction of increasing drift.

The figure shows the total equivalent forces, when a high-friction differential is installed on the machine. A high-friction differential transfers more than half of engine’s torque to rear loaded wheel. The increased traction on rear loaded wheel pushes the car even deeper in the direction of drift (to the left in the figure plane). An addition increase of the torque on rear loaded wheel leads to an increase of engine power transmitted to this wheel.

Thus, the same time pressing the throttle and brake pedals on a rear-drive car creates understeer and allows you to get out of drift. In the future this method of fighting with drift on a rear-wheel-drive car will be called a defensive “throttle+brake” technique. As a rule, at drift angle of approximately 45 degrees (the angle must be checked for each car) and more “throttle+brake” technique does not work, since traction on rear loaded wheel causes car to turn around.

It is important to understand, that “throttle+brake” technique forced a car to move straight. When performing the technique drifting stops, the machine continues to move in a straight line in the same direction, in which it was moving before performance the technique. Therefore it is necessary to calculate trajectory and duration of “throttle+brake” pulse. If a driver has reacted to drift in time, a short impact on the brake pedal and steering correction may be enough. Note, that “throttle+brake” technique allows you to get out of drift, without turning the front wheels.

Since the front wheels are locked, it does not matter, which way they are turned. But to successfully take control at the end of the technique, when the front wheels are in locked condition, you should put the steering wheel straight. There are two reasons for this:

• the suspension geometry is such, that when the front wheels are turned by the steering wheel, the front of car come down; the straighten wheels will lift the front of car back; the greater front clearance — the lower steerability;

• if the front wheels are set in the straight position, car will remain neutral behavior after releasing the throttle and brake pedals (the car’s behavior will not change).

At the end of “throttle+brake” technique it is enough to align trajectory with a corrective steering. If it is necessary to avoid an obstacle or bend trajectory because of other reasons, you should turn the front wheels previously, during perform the technique, when the front wheels are locked.

The torque transmitted to rear loaded wheel depends on engine torque. If engine torque is high enough, efficiency of “throttle+brake” technique may fall: when together pressed the throttle and brake pedals the rear wheels start to skid. In this case to exclude skidding of rear loaded wheel, you should limit effort on the throttle pedal during performance the technique.

For “throttle+brake” technique to work on a rear-wheel drive car, the brake system must be properly configured. It is necessary, that both front wheels are locked when the brake pedal is fully pressed both when moving forward in a straight line, and when passing corners to the left and right or when the car is in a drift. In addition, the braking effort on the rear wheels should not be too high, and engine torque should not be too low. If the rear wheels will be locked, the engine will stall.

Requirements for successful exit from a drift on a rear-wheel-drive car with help of “throttle+brake” technique

• both front wheels must lock when the car is in a drift;

• the rear wheels must not be locked;

• skid of rear loaded wheel should not occur;

• differential friction should not be too high;

• drift angle should not be greater, than about 45 degrees.

The last two requirements are very conditional. Performing of the technique may differ on different machines, so you need to perform concrete tests. It is not difficult to test “throttle+brake” technique: you just need to provoke a drift and press the throttle and brake pedals.

It was not said, but was obvious, that to perform the above-listed techniques an anti-lock system should not be installed on car, which prevents the wheels from locking by the brake system. In the presence of an anti-lock system it is impossible to perform defensive “throttle+brake” technique on a rear-wheel-drive car.

Recommendations for driving a car in a drift

• while driving car in a drift, your hands should be relaxed, you do not need to hold the steering wheel with a death grip;

• while drift turn your head and direct your gaze along the direction of movement of car, keep the hood in the background, so you will definitely feel angle of drift;

• when fighting with a deep drift direct your gaze forward, through the windshield — this will help you maintain your orientation in space.

Notes on performing of “throttle+brake” defensive technique on a rear-wheel-drive car

• during perform the technique you should to straighten the front wheels or turn them by the steering wheel in the direction, in which you want to continue move at the end of the technique;

• if the engine torque is quite high and the rear wheels start to skid when performing the technique, you need to limit effort on the throttle pedal: the traction on the rear axle is only needed to unload the front;

• the duration of the technique is controlled according to trajectory of movement.

Exercise 1. Work out the skills of getting out from drift with help of steering. Actions will vary depending on the type of drive: on front-wheel-drive type it is necessary to increase the traction and to turn the steer against direction of drift, on rear-wheel-drive — you need to let go of the throttle pedal, press the clutch pedal and direct the front wheels in the direction of motion (you should to rotate the steer against the direction of drift until desired position of the front wheels).

Be careful! When exiting a drift on a rear-wheel-drive car there should not be a long pause after turning the steer against direction of drift. Otherwise there may be a response from the car, and there will be a rhythmic drift. As soon as drift has started to stop, you need to immediately return the steer to the “straight” position.

Exercise 2. Create oversteer on a front-wheel-drive car at the entrance to a long corner (arc) with help of “throttle+brake” technique. Repeating the training, try to gradually increase speed of entering the corner.

Exercise 3. On a rear-wheel-drive car, press the throttle pedal at the exit of a corner, to trigger drift. Without releasing the throttle pedal, sharply hit the brake pedal with your left foot, to eliminate the drift. After stopping drifting release the pedals and restore trajectory by the steer motions. Repeating the exercise, determine angle of drift, more than which the technique “throttle+brake” does not work. Limit effort on the throttle pedal if there is a skid of rear loaded wheel and efficiency of “throttle+brake” technique decreases.

Remember that on a front-wheel-drive car one time pressed the throttle and brake pedals increases steerability, while on a rear-wheel-drive car — they decrease it. If this is the first time when you are perform the technique, limit speed and provide braking distance enough in all possible directions.

Exercise 4. On rear-wheel-drive or all-wheel-drive cars, prepared for drift, the exercises “ring”, “eight” and the passage of a hairpin with drift of the rear axle will be useful. Rings should be selected in different diameters to work out different speed modes.

We press the throttle pedal with pulses, as if groping for optimal traction, and at the same time we steer. Our goal will be a stable retention of trajectory radius and minimal fluctuations in drift angle.

Exercise 5. Go through a 180-degree turn (hairpin) with the rear axle drifting. At entrance to the corner provoke drift by rocking, handbraking or including a low gear.

At exit of the corner maintain drift by alternately pressings the throttle pedal. Try to get maximum acceleration at exit of the hairpin.

Exercise 6. Another useful exercise for training driving a car in a drift is the “eight”. In the middle of the eight we perform the so-called reversal: we accelerate car, then release the throttle pedal and rotate the steering wheel in the opposite direction when moving to the next half of the eight.

If there is feedback on the steer it should start to rotate itself against the direction of drift. The feedback force depends on the castor in a car and settings of the feedback force in a car simulator.

Exercise 7. Try to cause the front axle to drift while reverse moving by sharply turn of the steer. Do not forget to squeeze the clutch, so that the engine does not stall during skidding.

Practical advices for a driver

1. Use light footwear with soft, non-thick, flat soles for driving. Rightly chose footwear will help you feel the pedals better. In any case do not drive a car in “flip-flops”, slippers or shoes with a long heel, this can lead to an accident situation. If footwear has a heel, it should not be long. Shoelaces are also dangerous. Scarves, ties, long sleeves, hair, and wired headphones can also interfere for driving.

2. Wear gloves while driving. In gloves with a rubberized palm (so-called “dipped” gloves) or leather gloves hands cling better to the steering wheel and the gear lever, and hand tires less during driving. If you are a novice racer, you may get « dipped” gloves for training, which you can buy at any building supplies store.

3. Place your hands on the steering wheel at 9 and 15 o’clock or 10 and 14 o’clock (according to the clock face). In these positions you can comfortably rotate the steering wheel within about 200 degrees. If you need to turn the steering wheel at a greater angle — continue rotation of the steer with change of hands position. A steering error will be crossing of hands in the lower sector of the steering wheel.

4. Use right steering wheel. Spokes of the steer should not prevent hands from being placed in the 9 and 15 o’clock or 10 and 14 o’clock positions and fingers from squeezing the steering wheel in these positions. It is possible placing of the spokes, in which they pass under or above hands — so you will feel right position of hands on the steer. It is not recommended to use a steering wheel cover, as it will dull feels, received from the steering wheel.

5. Take into account condition of the road surface to choose speed of movement. Let us assume, that you are on an unfamiliar road or road state may have changed significantly recently due to weather conditions. You may estimate condition of the road surface with help of braking with wheels locking. At low speed (10—15 km/h), hardly press the brake pedal to lock the wheels, and wait for stop. The worse the grip, the greater braking distance. When you get more experience a short-time wheels lock will be enough to estimate a road surface. This skill is very useful in winter: for example, a situation may be when the road is snow covered, and there — is bare ice under the snow, which a driver does not suspect.

6. Do not listen to music when driving. This takes away your attention and impairs your concentration on driving. The same applies to conversations on cell phone. A missed beep or even a scream can cause inconvertible events.

7. Do not move in neutral gear. Some drivers, trying to save on fuel, move downhill and enter corners in neutral gear. This makes driving a car unsafe. Disconnecting the engine from the transmission makes it impossible to control a car with help of engine’s torque. The throttle pedal — is a very important element of controls in both front-wheel-drive and rear-wheel-drive vehicles.

8. Do not keep your hand on the gear lever. Many drivers drive in city traffic a car with a standard gear box in a relaxed pose, when left hand is on the steering wheel and right hand — is on the gear lever. Both hands should be placed on the steering wheel. Right hand moves to the gear lever only when it is necessary to change the gear.

Turnaround while reversing (police turn)

Police turn is familiar to many from films. It is rumored that drivers of the special services keep it on board. Police turn allows you to quickly turn a car around with help of front axle drift, which can be created while driving in reverse.

Despite seeming from the outside difficulty of the technique, it is quite simple to perform. Consider performing the technique on front-wheel-drive and rear-wheel-drive cars.

Rear-wheel-drive

Firstly it is necessary to select the reverse gear and accelerate along a straight section of trajectory. It should be noted, that during reversing after releasing the throttle pedal the engine starts braking. Engine braking — is a braking torque (some kind of braking effort). Braking on the rear axle while driving in reverse creates understeer, similar to how high braking effort on the front wheels causes sliding of the front axle when driving ahead. Therefore after performing acceleration it is necessary to disconnect the engine and transmission before performing the technique.

To produce drift of the front axle, you need to quickly turn the steer. After drift occurs, wasted no time, it is necessary to immediately return the steer to the straight position. When longitudinal speed will be zero, the first gear can be switched on. Let us show at the figure performance of turnaround.

Initially we were moving in a straight line in reverse, but deviated from the straight line and after performing turnaround left the marked lane. Drifting of the front axle did not begin immediately: at beginning turn of the steer the car deviates from straight trajectory.

To stay in the lane, during acceleration it is needful to slightly deviate from straight line movement with a short movement of the steer to the side, opposite to direction of turning. It is important to do this during acceleration — if there is no traction on the rear axle when the steer deviates from the “straight” position, the car will start to turn around. Preliminary shift in the opposite side not only increases space for maneuver, but also intensify further sliding of the front axle due to rocking. Let us show at the figure performance of reverse turn with a preliminary deviation.

As you can see, we succeed to stay within the marked lane.

If a car does not respond well to performing police turn, you can use at one time pressing of the throttle and brake pedals. Engine torque, transmitted to the rear axle, will prevent the rear wheels from braking, but high braking effort on the front wheels will lock them, causing a car to turn around. Let us illustrate at the figure reverse turn perform using the throttle and brake pedals.

Front-wheel-drive

On a front-wheel-drive car engine braking when reversing creates oversteer. We should seize this. But so that the engine does not stall during perform the technique, it is necessary to press the clutch, when engine speed drops to idle. Let us show at the figure performing a turnaround on a front-wheel-drive car.

Preliminary deviation should be performed by a very short and smooth steer motion, as a car may start to turn around. On rear-wheel-drive traction on the rear axle protects from turning, which is not present on a front-wheel-drive car during acceleration.

Regardless of the type of drive, some machine settings contribute to perform of turnaround. Shifting the center of mass to the rear axle (a small proportion of the weight on the front axle) will make it easier turn of the front axle around the rear axle. Besides, the more a car shows understeer when driving ahead, the more oversteer will occur when driving reverse. Therefore understeer will be another positive point for performing a police turn. So, factors, that affect steerability when driving in reverse are as follows:

• shifting the center of mass to the rear axle;

• understeer when moving ahead.

Steerability when moving reverse affects on success of turnaround performance. A turnaround while reversing can be performed with help of a rightly set of the brake system.

Exercise 1. Try to perform a police turn on a rear-wheel-drive vehicle in all the ways, described in this chapter. Which of the ways to perform a turnaround is the most optimal for your car?

Exercise 2. Perform a police turn on a front-wheel-drive vehicle. Be careful when performing a preliminary deviation, as front-wheel-drive vehicle shows oversteer during reverse acceleration (opposite to a rear-wheel-drive vehicle, which shows understeer during reverse acceleration).

Exercise 3. What settings must be changed, to increase car’s steerability when reversing? Test steerability of reversing at different settings.

Return from an obtuse drift angle

Turnaround of a car on the road is unlikely, but it can be quite dangerous, if it happens for some reasons when moving at high speed. When sliding at a large angle (90—180 degrees), it is impossible to control trajectory of movement and predict behavior of machine. An untrained driver will not be able to take any correct actions during turnaround of a car to overcome drift.

It is known, that on a front-wheel-drive car it will not be difficult to get out of almost any drift angle — it is just needful to press the throttle pedal and turn the steer. For a rear-wheel-drive car there is an effective “throttle+brake” technique, but drift angle, which can be overcome by this technique, is limited. Regardless of the type of drive, machine can be quickly returned, using dosed braking effort in definite range of drift angles.

Let us try an experiment. We will move around a ring in reverse. While moving, press the brake and clutch pedals all the way down.

The sports car’s braking system is very powerful and can lock both the front and rear wheels. After pressing the clutch and brake pedals all the wheels locked, and the car continued to slide move in a straight line. The front wheels locked a little earlier than the rear ones. The final position of the body is at small angle relative to the initial position. Let us repeat the test with less effort on the brake pedal.

When the brake pedal was pressed, both the front wheels and rear left wheel locked. The car almost turned around. If initial speed of movement was greater, the car would most likely perform a turnaround before stopping. Braking efforts on both rear wheels are the same, but at the beginning of braking weight of the car puts more pressure on rear right wheel, than on rear left wheel. Therefore braking effort, which should lock right rear wheel, must be higher, than braking effort on the rear left wheel. In the next test we will push the brake pedal even more weakly, but we will try to provoke lockage of the front wheels.

After pressing the brake pedal both front wheels locked, both rear wheels rotate, until the car stopped. The results are similar to the previous test: the car began to turn around after pressing the brake pedal. On all cars, as a rule, brakes of the front wheels are much stronger than brakes of the rear. If the brake system is correctly set, when the brake pedal is fully pressed when moving on an asphalt road in reverse in a corner or in an obtuse slide angle both front wheels must lock, and the rear — continue to rotate.

Based on the previous experiments, let us formulate test for performing a car turnaround with help of the brake system.

Turnaround test when reversing with help of the brake system. While reversing around a ring, abruptly push the clutch and brake pedals to the end. Both front wheels must lock, rear loaded wheel must not lock. After pressing the pedals car should turn around.

Locking of the front wheels when the brake pedal is pressed must occur for any level of wheel loading. For example, when a car move in a drift, the body rolls, and some wheels are loaded, others — are unloaded. If the braking system is weak, front loaded wheel may not lock.

The test must be performed in clockwise and counter-clockwise move directions, since the braking system can work “criss-cross”, creating slightly different braking efforts for wheels on the same axle (depending on correct setting of the braking system).

Practice shows, that turning around with help of the brake system is not effective, if drift angle is close to 180 degrees or equal to 180 degrees (reverse moving). When pressing the brake pedal the front wheels lock, there is braking effort on the rear wheels, but car will not turn around. Therefore firstly it is necessary to deflect trajectory by turn the steer, after which already lock the front wheels with the service brake. In addition, drift angles in range of approximately 90—140 degrees are also unsuitable for performing turnaround using the brake. While moving in drift at these angles rotation speeds of wheels is low and their locking will not significantly change angle of drift.

On a rear-wheel-drive car you can increase angle of drift, if you cause the rear wheels to skid (gain engine speed in first or second gear and release the clutch pedal). On a front-wheel-drive car wheels skidding should reduce drift angle. On both front-wheel-drive and rear-wheel-drive vehicles the torque and inertia moment of the engine should be enough to cause the drive wheels to skid. In addition, to create skidding of driving wheels, anti-skid system (traction control) should not be installed on car.

The figure shows performing turnaround using the brake, when the car is moving in deep slide. In the chapter “Turnaround while reversing (police turn)”, it was noted, that the success of turnaround is affected by reverse steerability, namely — it should not be too low. The same requirement applies to performing turnaround with help of the brake.

Requirements for successful return from an obtuse drift angle with help of the brake system

• when moving in an obtuse drift angle after pressing the brake pedal to 100%, the front wheels must lock, rear loaded wheel must maintain rotation;

• drift angle should be high enough, but should not be close to 180 degrees (reverse moving), approximate angle range — is from 140 to 160 degrees;

• steerability of reverse moving should not be too low.

Let us try another experiment. When the car is in drift (angle of about 150 degrees), turn the steer to stop in direction of increasing drift angle. We will assume, the car is moving in neutral gear or with pressed clutch pedal, and the front wheels are in the “straight” position.

As we can see, after turning the steer the car began to slowly turn around. Trajectory was slightly curved. Tyre traces were interrupted, as the car moved almost in reverse for short distance. Steer turn allowed not only to turn around, but also to bend trajectory against the direction of drift. We observed similar trajectory bending, when performing a police turn (trajectory bending was undesirable, we tried to eliminate it with help of preliminary deviation).

Let us compare two ways of return from drift with an obtuse angle: by locking the front wheels and turning the front wheels.

Left part of the figure shows turnaround, made by locking the front wheels, and the right part — shows turnaround, accomplished by turning the steering wheel (police turn). Turnaround of the car with help of the brake system is faster and trajectory is generally close to straight line. The second method, unlike the first, allows you to deflect trajectory in the direction, where rear part of car looks when moving in drift (when the front wheels are locked, there is also deflection of trajectory, but it is very small). Moreover the higher steerability when reversing, the faster turnaround will occur after turning the steer and the less curvature of trajectory will be.

Aerodynamic elements, which increase side resistance to air movement of rear part of the body, can contribute to passive safety of a car.