CAPITAL L C A H N A O P I T T E A R N DRIVERS SCHOOL

B M A W IC C ER AR M CLUB OF A

Car Control Clinic

Welcome to the National Capital Chapter’s Car Driving Theory Control Clinic. This unique drivers’ school is designed to introduce you to the fundamentals of car control and Before we begin, let’s take a few moments to driving mechanics in a safe environment. We’ve con- understand what actually happens when driving. Most structed a series of driving exercises that are designed to of us don’t think about driving; it’s enough that when we provoke certain behaviors from your car. Each exercise point our car in a certain direction and step on the illustrates a particular characteristic response of your accelerator, the car goes where it’s pointed. As long as car to road conditions and driver input. You’ll learn nothing goes wrong, that’s sufficient. However, our proper and improper driver inputs for particular situa- lack of knowledge works against us in emergency tions. By the end of the day, you’ll have a better situations. understanding of how your car behaves under braking and cornering, where the limits of adhesion are, and how You may have lost control of your car at some to work safely within them. point in time. Perhaps it was raining or snowing; you entered a curve a little too fast, turned the wheel, but You will be scheduled for exercise, classroom, your car kept going straight ahead. Or maybe you had to and skidpad sessions. Classroom sessions will cover the jam on your brakes suddenly and hope that you’d stop underlying principles behind each of the exercises: before hitting the car in front of you. In any case, you what your car’s tires are doing while you’re negotiating know that helpless feeling of being “along for the ride” the exercise, how your steering and acceleration inputs with no control over what’s happening. affect your car’s behavior, and why some of your inputs work and some don’t. Skidpad sessions will allow you What went wrong was that you asked your car to to experience and practice recoveries from loss-of- do something it couldn’t do, either negotiate a curve at adhesion situations in a safe, controlled, low-speed too high a speed or come to a stop in too short a distance. setting. You’ll also learn why your instincts in such Physical laws govern the behavior of your car, and situations are almost always wrong. understanding those laws is the key to controlling your car. At the school, we’ll show you—and let you expe- This publication describes the purpose of the rience—the physical limits of your car’s ability to turn exercises we’ll be doing; refer to the map on the last or stop. Most importantly, by experiencing and under- page for the exercise locations. The exercise area has standing these limits, you’ll know what options you been split into two loops: a braking loop and a slalom have in an emergency. loop. We will run the loops simultaneously. Each exer- cise will involve guiding your car through a series of Fundamentally, driving is all about friction— pylons (cones). specifically, the friction between your tires and the pavement. When you depress the accelerator, or apply Don’t worry about hitting the pylons we use to the brakes, or turn the steering wheel, your tires generate mark the exercises. They’re short and made of soft frictional forces which are applied to your car to accel- plastic, so they won’t hurt your car. What may hurt your erate, decelerate, or change directions. Each specific car is if you lose control while trying to avoid hitting a demand you make on your car (e.g., turning a corner) pylon. Always maintain control of your car, even if it requires a certain amount of force. Your car requires the means running over every pylon in an exercise! least amount of friction with the pavement when travel- ing in a straight line at a constant speed. Accelerating,

Copyright © 2009 National Capital Chapter BMW CCA, Inc. All rights reserved. Revised June 2009 braking, or turning require more friction, with larger on differential surfaces, i.e., where the tires on one side speed or direction changes (e.g., braking harder or of the car are on a slipperier surface (e.g., grass) than the turning sharper) requiring proportionally larger amounts tires on the other side (e.g., pavement). of friction. If your tires cannot generate sufficient fric- Second, ABS cannot manufacture more friction tional force, your car will not do what you want. than is available; it can only make the best use of what there is. That means that if you have engaged the ABS Threshold Braking and attempt to turn, the car’s response will be sluggish. This is because available friction is being divided be- When you apply your brakes, the frictional forces tween braking and turning. If the surface adhesion is generated by your tires act to slow your car down. The low, e.g., on wet pavement, turning will be largely harder you press on the brake pedal, the larger the ineffective. You actually must reduce your braking to generated force is, and the faster you slow down—to a give your front tires more of the available friction. This point. If you press too hard, your tires will be unable to might allow you to avoid an obstacle directly ahead generate the force being demanded of them, and they (e.g., a tree), whereas maintaining full braking would will lock (i.e., stop turning and begin sliding along the not allow you to stop in time to avoid the impact. It is pavement). This sliding still generates some friction, very counterintuitive to lessen your braking in an emer- but it is important to note that it is less than the amount gency, so we have designed exercises where you can that was being generated just before they locked. practice this. Therefore, the quickest way to slow your car is to depress the brake pedal with as much pressure as is Handling possible without locking your tires. This technique is called threshold braking. However, it is difficult to Two important aspects of your car’s handling are control precisely the amount of pressure you apply to balance and weight transfer. Balance is how your car’s the brake pedal, and it’s even tougher if you’re trying to weight is distributed from front to rear and from side to turn the car at the same time. Threshold braking is a side. The weight of your car generates proportional technique that takes a lot of practice to master. frictional forces (grip) at each tire, and these forces change profoundly when you accelerate, decelerate, or Because untrained drivers have difficulty braking change direction; this is called weight transfer. with maximum effectiveness, and because most folks do not have the opportunity to learn threshold braking When you accelerate, weight transfers to the rear before they need it in an emergency, antilock braking of your car, decreasing the grip available to your front systems (ABS) were invented. If you apply too much tires and increasing the grip available to your rear tires. brake pedal pressure, the ABS will modulate the pres- When you decelerate, weight transfers to the front of sure for you; you can feel this as a pulsation in the pedal. your car, enhancing front tire grip and decreasing rear ABS works to keep your braking near maximum effec- tire grip. In a turn, weight transfers to the outer tires, tiveness if you press hard enough to engage it. reducing the grip of your inner tires. The amount by which grip changes at each tire in response to weight However, ABS has limitations. First, it is a bit less transfer is determined primarily by your car’s suspen- effective than braking at the threshold of ABS activa- sion and its reactions to your inputs. tion. That is, braking effectiveness drops off slightly when ABS is fully engaged. This is because the system For a given corner taken at a given speed, each of must release the brakes for a moment to allow the your tires requires a certain amount of grip to maintain wheels to begin turning again. Braking with ABS oper- adhesion with the pavement. Higher speeds and tighter ating is better than braking with insufficient brake corners require correspondingly more grip. If weight pressure, or with too much pressure (locked wheels), transfer causes the grip available at a given tire to but not quite as good as a trained driver braking at the decrease below that which is required, it will lose threshold. If you learn where the threshold is and can adhesion and begin to slide against the pavement. If the maintain your braking at that point, you will stop in sliding tire is at the front of your car, your car will shorter distances. This is especially true when braking understeer; if it is at the rear, your car will oversteer.

2 Car Control Clinic Understeer, or “push,” occurs when your front is counterintuitive, because the last thing you’ll think tires lose adhesion with the pavement. Instead of fol- you need at that point is more speed. However, when lowing your intended path around the corner, your car you accelerate, you transfer weight back onto your rear will begin to run wide, as though you were steering less tires, giving them more grip. It’s important to recognize than you needed to. Understeer is often caused by here that you’re applying acceleration not to increase entering a corner too fast or by turning the steering your speed, but to restore your car’s balance. wheel too quickly: both upset the balance of your car.

Oversteer can be caused by sudden deceleration in The important thing to realize is that understeer a corner, either by braking or by coming sharply off the occurs because your front tires are overloaded—they accelerator, causing weight to transfer away from the require more grip to maintain adhesion than is available. rear wheels. This often occurs when you enter a corner Steering more, i.e., trying to turn a tighter arc, simply too fast; the solution is to enter more slowly, so that you overloads them more, making the understeer worse. To can maintain your car’s balance throughout the corner. correct understeer, you must restore adhesion to the Oversteer in a rear-wheel drive car can also be front tires by slowing your car and/or straightening the caused by applying enough acceleration to break the steering wheel a bit; both reduce the grip required. rear wheels loose. This occurs most frequently under Straightening the wheel is counterintuitive, because conditions of reduced adhesion (rain), but it can also you’re deliberately steering toward the outside edge of occur under good conditions if your car is powerful the pavement, but you must regain front-end adhesion enough. In this case, you must reduce your acceleration before you can change your car’s direction effectively. slightly to allow your rear tires to re-adhere. If you Oversteer, or “looseness,” occurs when your rear reduce your acceleration too much or too rapidly, weight tires lose adhesion with the pavement. Instead of fol- will transfer away from the rear, and your car will lowing your intended path around the corner, your car continue to oversteer. To avoid inducing oversteer, will begin to rotate around your front tires, as though accelerate smoothly and progressively. you were steering more than you needed to. To stop the We’ve designed several exercises that demon- rotation of your car, you must apply a countering force strate weight transfer in various ways. Your skidpad by steering toward the outside of the corner. You must sessions are also designed to demonstrate understeer also maintain your speed or accelerate slightly. This too and oversteer and the techniques used to overcome

Car Control Clinic 3 them. Remember: anything you do to upset your car’s Before you leave for the exercise pads, please balance may transfer enough weight to cause understeer double-check the inside of your car and be sure to empty or oversteer. That’s why we will emphasize smoothness it of anything you might have put back in after tech throughout your school. inspection. Check especially the glove compartment, map pockets, center console, and on the floor behind the Where to Look seats. We don’t want anything loose banging around while you’re driving the exercises and distracting either Whenever you’re driving, you should watch where you or your instructor. you’re going. This seems obvious, but you’d be sur- The exercise pad is divided into two loops. Viewed prised how much time you spend looking at where you from the pad entrance at the exercise parking area, the are—specifically, at the pavement or car immediately in left-hand loop is for the braking exercises, and the right- front of you—instead of where you are about to be. hand loop is for the slalom exercises. Both exercise Because your brain takes a moment to digest new loops will be reset for the afternoon, so you’ll have information and command your muscles to react, look- different exercises in each half of the day. In the morn- ing immediately in front of your car in an impending ing, you will rotate among the two exercise loops and accident serves only to tell you what you’re going to hit the skidpad. After lunch, we will return to the classroom instead of what you could have avoided. to cover the afternoon exercises before returning to the At the school, we’ve marked the exercises with exercise pads. Again, you will rotate among the two pylons, and it’s very important not to look at the pylon loops and the skidpad. you’re about to pass but rather at the next pylon coming up. To counter the delay between the time you see something and when you react to it (called your reaction Morning Slalom-Loop time), you must look and think ahead to avoid problems. Exercises At all times, both at the school and on the road, you should keep your vision and your thinking about one to We will run several students on the exercise loops one and a half seconds ahead of your current position. simultaneously. Please watch out for each other and be sure to wait until the student ahead of you has cleared the exercise before you enter. If that student knocks down Preparing for the Exercises one or more cones, please allow the course worker a moment to replace them and retreat before you begin. When you arrive at the facility, please check in You will have several passes at each loop, so that you with our registrar, Doug Verner, in the classroom build- can refine your skills. ing. Then return to your car and empty the interior and trunk of all loose items. You may leave your parapher- nalia in the classroom building until the end of the Exercise 1—Straight Slalom (Equal school. Once everything is out of your car, drive it to our Spacing) technical inspection area, which will be in the same parking lot. We’ll do a quick safety inspection to make A slalom is a set of spaced pylons in a line. The sure everything is OK, and then you can park it again in object is to drive around the pylons, alternately passing the lot. them on the left and right, while holding a constant speed. After each successful pass though the slalom, After tech inspection, we will have a class for all increase your speed a little bit. students to explain the exercises. The class will discuss the general principles presented above, as well as the As your speeds increase, you’ll find it harder to specifics of each exercise. After the class, students will avoid running over the pylons. This is because your car break into three assigned groups and drive from the requires a finite amount of time (called the transient classroom facility to the exercise pads, which are about response time) from the moment you turn your steering 0.7 mile north on Slacks Road. Your instructors will wheel until your car actually changes direction. First, meet you there and direct you where to park. the sidewalls of your tires must flex. Then the springs 4 Car Control Clinic and bushings in your suspension must compress. Fi- at the second to avoid hitting the pylon. If you’re going nally, your car will begin to change directions. The too fast, you won’t be able to make the turn sharp faster you go, the more distance you cover before your enough, so you’ll be late for the second as well, and the car reacts to your steering input. third turn will have to be even sharper. This can easily cascade, and unless corrected, you may run out of room near the last pylon. To execute the slalom properly, you must enter at a speed slightly slower than you think is necessary, smoothly turn the steering wheel slightly before reach- ing each pylon, and maintain or slightly accelerate to keep the weight balanced from front to rear. If you find yourself going too fast, recognize the symptoms early and abort the slalom by straightening your wheel in- stead of turning back for the next pylon. Run over one or more pylons if needed but maintain control of your car.

Exercise 2—Curved Slalom (Increasing Radius)

This is similar to Exercise 1, but this time, you’ll be going through a curve at the same time. Whereas the The key, then, is to anticipate this delay in your straight-line slalom requires you to steer right and left car’s reaction and turn slightly before you reach the next with a similar amount of steering input in each direction, pylon, much as a skier turns his skis just before a gate. this slalom will require much more steering input and The faster you go, the earlier you will have to turn. effort to turn to the inside of the corner than to the outside. This is because the line of cones curves to meet When you turn your car from side to side, you are you when you turn out. As with the straight-line slalom, transferring weight to alternate sides of your car. In smoothness and proper entry speed are the keys. doing so, the springs on the side opposite the direction you’re turning (called the loaded side) will compress. Until your suspension has fully compressed, your loaded- side tires will not achieve full adhesion. Final compres- sion will occur most rapidly if the turn is executed smoothly; if you turn abruptly, your loaded-side springs will actually compress too much, then expand again (or rebound) before finally settling down. During this time, you will not have maximally effective control of your car. If you enter the slalom too quickly, you will find that you must reduce your speed to negotiate the first turn. However, when you decelerate, weight transfers forward, and rear-tire adhesion decreases. If enough weight transfers forward, you could spin. Note that more weight transfer will occur when you turn to the inside, and your car’s transient response Moreover, any errors in placement that you make time will be correspondingly longer, so time your steer- will multiply at each turn. That is, if you are late turning ing inputs accordingly. for the first pylon, you will have to make a sharper turn

Car Control Clinic 5 Exercise 3—Straight Slalom Exercise 4—Threshold Braking (Unequal Spacing) This exercise gives you a chance to practice thresh- This slalom has the cones set a varying distance old braking. Accelerate briskly down the straight. When apart. Therefore, the amount of turning you’ll need to do you reach the first of the pylons, begin braking and come will vary from cone to cone. to a stop as quickly as possible. The row of pylons next to your car will serve as a “gauge” of how quickly you’ve stopped. The faster you approach the braking pylons, the longer your braking time will be, giving you more practice time.

If your car does not have ABS, ensure that you are not locking one or more wheels by braking too hard; you want to have them on the threshold of lockup, where braking effectiveness is maximal. If your car does have ABS, then you want to press the pedal hard enough to The key here is to look ahead so that you will have engage it. When engaged, you’ll feel a rapid pulsation time to plan your next turn. If you look only at the cone in the brake pedal. This is normal and is the action of the you’re currently approaching, you won’t be set up ABS modulating brake pressure to maintain the wheels properly for the following cone. Always look one cone at the lockup threshold. Work to determine the exact ahead of your current position. amount of pressure needed to begin ABS activation; this is the threshold point. Morning Braking-Loop You will want to concentrate especially on mini- mizing the transition time, that is, the time it takes you Exercises to switch from acceleration to full braking. This time directly translates into distance covered, and the faster Each braking exercise requires you to brake and you react, the shorter your braking distances will be. come to a complete stop before continuing. Generally, you will want to accelerate briskly to maximize your speed before braking. The faster you go, the more time Exercise 5—Braking While Turning you will have to work on your braking skills, which translates into more rapid learning. Work with your This exercise is designed to illustrate that braking instructor to stop as quickly as possible, consistent with and turning simultaneously requires a tradeoff between maintaining control of your car. stopping ability and cornering ability. You will have to split the friction available to your tires between slowing your car and changing directions. You control this split by how much pressure you put on your brake pedal.

6 Car Control Clinic ahead, because if you stare at the first center pylon, you may turn sharply enough to avoid that pylon, but by the time you look up, it will be too late to turn back to remain in the designated lane. Instead, focus on the last center pylon and be prepared to shift your vision to the last pylon on the right or left as needed. Use your peripheral vision to guide your car into the proper lane.

When you get to the first of the pylons, switch from acceleration to maximum braking while continu- ing to steer the car around the corner. Try to come to a complete stop before reaching the last pylon. Note that your car’s weight will be transferring forward from braking, as well as to the left from turning. This means that your left-front tire will be most heavily loaded (generating the most friction), and your right- rear tire will be most lightly loaded (generating the Try to remain relaxed and alert as you approach least). If you detect the rear tires losing adhesion, reduce the exercise, and try not to decide which way you’re your braking pressure; this will transfer weight back to going before your instructor tells you. With each pass, the rear and increase their adhesion. It is more important your instructor will delay his command more. to maintain control of your car than to stop by the last pylon, so run wide or overrun the pylons in preference to transferring too much weight off the rear wheels and Exercise 7—Lane Change spinning your car. As you approach, drive between the first pair of Exercises 4 and 5 are repeated for the second half pylons and then steer toward the second pair. As you of the braking loop. reach them, steer to straighten out the car and pass

Afternoon Slalom-Loop Exercises

Exercise 6—Obstacle Avoidance

In this exercise, you’ll simulate making a last- second maneuver to avoid an obstacle on the road. The exercise area will be divided into two lanes. Approach the exercise by driving toward the center pylons. At the last moment, your instructor will either say “left” or “right” or point to the lane you are to use. Steer into the lane your instructor indicates and continue through the exercise without braking. You will have to manage weight transfer and your car’s transient response time. You will also have to look

Car Control Clinic 7 between them. As you pass through the third pair of implications. First, as before, it will be harder to turn to pylons, steer again toward the fourth pair. Finally, steer the inside of the corner than to the outside. Second, the while passing between the fourth pair and exit the difference in steering input required for each pair of exercise without stopping. Maintain constant speed turns will increase. In the morning, you entered the through the exercise, and increase your speed slightly slalom slowly and accelerated as you traveled through with each successful pass. it. Now you’ll need to lose speed gradually as you travel through the slalom, so that the slowest point will be at Our familiar friends, weight transfer and transient the last pylon. The same principles of weight transfer response time, are in operation here. The key is to allow and transient response time are at work here, but they your car time to settle, i.e., restore its balance by will be magnified as the corner tightens up sharply near redistributing its weight evenly, between the second the final pylons. Be sure to look ahead so that you can and third pair of pylons. If you enter too quickly, your plan ahead. car will still be unbalanced when you attempt to turn back for the last pair of pylons, and it will be sluggish in turning (i.e., the transient response time will be longer). If that happens, do not attempt to force your car through Afternoon Braking-Loop the fourth set of pylons; if you attempt to slow down, Exercises you may transfer enough weight off the rear tires to spin. Instead, simply abort the exercise by straightening the steering wheel and driving past the pylons. Exercise 9—Braking While Avoiding (Offset) Exercise 8—Curved Slalom This exercise simulates avoiding an obstacle in a (Decreasing Radius) restricted area, such as a parking lot. You may decide to enter on either side of the center pylon. After you pass Although this setup is similar to Exercise 2, it will prove to be a lot harder. You will be slaloming through a curve, but now the radius will decrease. This has two

the first set of pylons, begin braking, steer toward the opposite set of pylons, and come to a complete stop between them. Your goal is to avoid hitting the center pylon of the second set by braking and turning as quickly as possible.

8 Car Control Clinic Exercise 10—Braking While Things to Remember Avoiding (Decision) First and foremost: maintain control of your car at This exercise is similar to Exercise 9, except that all times. The best way to learn your car’s limits—and your instructor will supply the avoidance direction. the only way we want you to learn them—is by working After entering between the first set of pylons, your up to them. If you drive “over your head,” you’re not instructor will direct you to the left or right of the center going to learn anything, and you’re going to endanger pylon. Begin braking, steer around the center pylon, and yourself and others in the process. come to a complete stop between the second set of Second, be aware of what’s going on around you. pylons. As with Exercise 6, try not to anticipate your You’ll need to listen to your instructor, but you’ll also instructor’s direction, but remain alert and ready to need to watch out for our course workers and other respond as quickly as possible. drivers. We don’t want you running over our workers; they’re hard to replace! Third, don’t be afraid to ask questions. We’ve packed a lot of information into a relatively small amount of time. If anything is unclear, if you have any questions at all about what your car is doing, or what you’re doing, or where you’re supposed to be, or whether your car is OK, just ask. If something doesn’t make sense, then we’ve explained it poorly, so ask us to clarify. All of us are here because we want to help you learn to be a better driver. Fourth, please fill out and return your school Remember that braking uses some of the friction evaluation. You’ll receive an evaluation form at morn- you will need to turn, and it transfers weight off the rear ing registration. Please fill it out and return it to the tires. If you brake too hard, you won’t be able to steer marked box in the classroom at the end of the day, or effectively, and you may unload the rear tires enough to fold it in thirds and mail it back to us. This is your school, spin your car. Executing the exercise correctly is a and the only way we can make it better is if you tell us matter of balancing the requirements of braking and what we did right and what we did wrong. Please help steering—that is, the front-to-rear weight transfer and us improve this program. friction. Finally, one last thing to remember: the Car Con- trol Clinic is supposed to be fun. It’s only natural to be Skidpad nervous at the start, but as you concentrate and learn, you’ll soon find that adrenaline and exhilaration replace Our skidpad program is explained in detail in the the butterflies. Pace yourself and enjoy the school. accompanying Skidpad Instruction publication. Most students are a bit nervous about their first skidpad session, but virtually everyone finds them immensely rewarding and instructive (the most common request we receive from students after the school is for more skidpad time). Skidpad training directly enhances your ability to control your car under adverse conditions. If you have any questions about the skidpad or our pro- gram, please do not hesitate to ask.

Car Control Clinic 9 Braking Loop Slalom Loop

AM Exercise 5 AM Exercise 2 PM Exercise 9

AM Exercise 1 AM Exercise 4 PM Exercise 6

AM Exercise 3 PM Exercise 7

AM Exercise 4 PM Exercise 10

AM Exercise 5 PM Exercise 8

The Maryland State Police Training Center 10 Car Control Clinic