Stopping and Turning  Responding safely in emergencies

You learned in the past two articles how to position yourself and your mirrors so you can see well and control the car effectively, and how different types of tires – and the tires’ air pressue and tread depth – affect the potential grip of the car on the road surface. Now we can talk about what you can do to control your Mercedes-Benz or other automobile and make your driving safe and enjoyable, as well as a means to get from one place to another.

Specifically, let’s talk about keeping the car under control when you’re making turns, when accelerating, braking, and when you need to do two of these things at almost the same time. The new and important principle to understand is something called weight transfer.

As illustrated in the graphics, pressing the accelerator transfers the weight of the car from the front wheels toward the rear wheels. When you apply the brakes, weight is transferred from the rear wheels to the front wheels. When you turn the steering wheel, weight is transferred to the outside wheels. The more abruptly you perform any of these actions while driving, the greater the weight transfer.

It’s important to know that the wheels that have more weight on them will grip the pavement more, and those that have less weight will grip the pavement less.



Clever automobile engineers have designed the suspension to absorb much of this weight transfer while maintaining a supple ride. The more recent models will even help you accelerate, stop, and turn more safely by automatically applying the brakes on one or more wheels if the car is in danger of going out of control.

The real problem is that the most important part of the system is the driver. By the methods learned and employed, drivers can avoid problems or they can make them worse. These principles can help your car corner more effectively while remaining under better control, ensure your passengers’ comfort, and make driving more enjoyable for you. Let’s look at some examples that are practiced in most safe driving courses, including the MBCA Education Foundation “Safe Drivers, Safe Families” Program.
 
Braking in a Straight Line

The simplest situation is one where you see an obstacle directly ahead of you, such as a car stopped in your lane, and you brake the car to a stop before you hit it. Even on dry pavement, if you’re going to fast or don’t notice the obstacle because you’re fiddling with your phone, you can have a problem; and it will be worse if the pavement is wet or icy.

As you apply the brakes, the weight of the car shifts forward so that the rear wheels are not in contact with the pavement as much as the front wheels. When this happens, the brakes can cause the rear wheels to stop moving. We often say that the brakes lock up, but in fact the wheels lock up when they lose adhesion. Once that happens, the wheels aren’t helping the car slow down. And without the rear wheels adhering to the pavement, like a boat without a rudder, the car is no longer steerable.

To deal with this problem in the old days, drivers were taught to rapidly release and reapply the brakes so that the wheels could start to spin again and regain adhesion with the pavement. However, few drivers have the opportunity or ability to learn how to do this effectively, and in the panic of an impending collision, might still lose control.

Mercedes-Benz engineers were among the first to try to help drivers solve this problem by inventing the anti-lock braking system (ABS). Sensors in the wheels sense a lock-up and the system then electronically releases the brakes for an instant, allowing the wheels to rotate again and regain traction. As soon as the wheels stop turning again, the brakes again will release. As this happens, you will hear a thumping sound and feel the brake pedal bumping at the same rate. As long as you keep the brake pushed down, you feel the brakes applying and releasing, applying and releasing, much faster than you could ever manage on your own.

The first exercise in prepararation for the unexpected is a deliberate panic stop to experience what the ABS system feels like when operating, and to get used to keeping the brake pedal down even as it vibrates under your foot, until your car has come to a complete stop. This exercise is included in most safe driving courses, but it’s worth practicing on your own on a deserted road or empty parking lot.

Incidentally, recent Mercedes-Benz research revealed that most people tend to release their antilock brakes and still hit some obstacles. So in the newest models, Mercedes-Benz engineers built in a supplementary system called Brake Assist that senses a true emergency from the speed with which you release the accelerator and stomp the brakes. It will keep applying the brakes, even if you release them.

The key point to remember here is when you apply the brakes, keep the pedal pressed to the floor until the car is stopped.

Braking and Turning

What happens if a sharp curve in the road catches you by surprise because you were distracted? You turn the steering wheel sharply, transferring weight to the outside tires, and off the inside tires, which reduces the amount of rubber trying to turn the car.

As shown in the illustration, instead of steering around the corner or the obstacle, the car continues to go in a straight line, a reaction called “understeer.” If the problem happens when you’re trying to turn right, you will cross into oncoming traffic, and that can be a disaster if something is coming toward you on the other side of the road.

On the other hand, if you then stamp on your brakes in panic after you’ve started to turn, then the weight of the car will also shift off the rear wheels, as you experienced when stopping in a straight line. At this point, with the car already turning, and the rear wheels now skidding instead of stabilizing the car, the momentum of the car can cause it to pivot around the outside front wheel (the one now carrying most of the weight of the car), especially on slick pavement, with the car spinning out of control. This situation is called “oversteer.”



If the car coming into the corner doesn't have sufficient weight on the front wheels when it turns because it is going too fast, it can understeer (car at left, top). If the car coming into the corner then applies the brakes, and/or the pagement is slippery, it will understeer (car at right, top).

You obviously can avoid this situation most of the time by paying attention when you’re driving, but in the event you do get into the problem, what you must do is to apply the brakes first, before you attempt to turn the car.

In the “Safe Drivers, Safe Families” program, we’ll practice the correct method for slowing first, then turning. As you get used to the routine, we’ll have you speed up to the point where you can feel your car’s advanced safety systems start to work to help you. Once you’ve pushed the brake, you just keep the brake pushed as hard as you can. You can then steer around the obstacle.

What you need to tell yourself, in any situation where you are going fast and need to slow the car and turn to avoid an obstacle, is to “stomp, stay, and steer.” First, stomp on the brakes. Second, stay on the brakes. Then, third, with the brakes still applied, turn the car.

With ABS, you will usually be able to slow the car and turn at the same time, even if the pavement is fairly slick.

Changing Lanes to Avoid Obstacles

The third emergency situation you might encounter is one where you’re going too fast to  slow the car enough to turn, such as when you see an obstacle in the lane ahead and there’s room on one side or the other so that you can steer around it. You can steer out of an emergency by focusing on where you want to go and turning the wheel toward that point. This is important, whether you are sliding sideways or someone else is coming toward you. Many studies prove that drivers will instinctively turn where their eyes are looking, so – don’t look at what you want to avoid.

In most advanced driver-training classes, students are given the chance to practice this exercise, as well, and the MBCA-EF program includes that exercise.

The newest Mercedes-Benz cars and several other brands have an electronic stability program (ESP)  that has have a “yaw sensor” and a steering position sensor in addition to the ABS wheel speed sensors. Yaw is the turning and leaning motion. By comparing the amount that the car is leaning and turning to the amount the steering wheel is turned, the car’s computer determines whether the driver is turning the wheel more (or less) than the direction the car is moving. As long as you keep trying to steer where you want the Benz to go, it will apply individual rear or front brakes to help the car turn in the direction you’re trying to steer.

Key Points to Remember

• Reduce the speed of the car first before trying to make a turn.
• If you are caught by an unexpected obstacle, it is still important to apply the brakes first, then steer the car.
• Once you apply the brakes, hold them down until the car has come to a safe speed or stopped.
• Finally, (and you will hear this often in any good driving course) steer with your eyes. The car will always go where you are looking, so focus on where you want to go.

Of course, not even a Mercedes-Benz can violate the laws of physics. If you aren’t paying attention when something bad happens, or try to stop or corner on slick pavement at high speed, not even all these assists will guarantee a safe result.

For more information about classroom and in-car driving courses visit mbca.org/ Education Foundation and Defensive Driving.

Jim Roberts, a member of the MBCA-Educational Foundation “Safe Drivers, Safe Families” task force, is a periodontist in Birmingham, Alabama, and a four-time Sports Car Club of America and seven-time Historic Sportscar Racing national champion race driver. He teaches high-performance driving for several national marque clubs and track-driving associations.