Any motorist knows that often we are separated from an accident in just a fraction of a second. A car moving at a certain speed cannot freeze in place, as if rooted to the spot, after pressing the brake pedal, even if you have Continental tires, which traditionally occupy high places in the ratings, and brake pads with high brake pressure.
After pressing the brake, the car still overcomes a certain distance, which is called the brake or stopping way. So stopping distance is the distance traveled vehicle from the moment of operation brake system to a complete stop. The driver must at least approximately be able to calculate stopping way, otherwise one of the basic rules of safe movement will not be observed:
- the stopping distance must be less than the distance to the obstacle.
Well, here such an ability as the driver’s reaction speed comes into play - the sooner he notices an obstacle and presses the pedal, the earlier car will stop.
The length of the braking distance depends on such factors:
- movement speed;
- quality and look pavement- wet or dry asphalt, ice, snow;
- the condition of the tires and braking system of the vehicle.
Please note that such a parameter as the weight of the car does not affect the length of the braking distance.
The braking method is also of great importance:
- sharp pressing to the stop leads to uncontrolled skidding;
- gradual increase in pressure - used in a calm environment and with good visibility, in emergency situations does not apply;
- intermittent pressing - the driver presses the pedal several times to the stop, the car may lose control, but stops quickly enough;
- stepped pressing - works according to the same principle, the driver completely blocks and releases the wheels without losing contact with the pedal.
There are several formulas that determine the length of the stopping distance, and we will apply them for different conditions.
dry asphalt
The braking distance is determined by a simple formula:
From the course of physics, we remember that μ is the coefficient of friction, g is the acceleration of free fall, and v is the speed of the car in meters per second.
Imagine the situation: we are driving a VAZ-2101 at a speed of 60 km / h. At 60-70 meters we see a pensioner who, forgetting about any safety rules, rushed across the road after a minibus.
We substitute the data in the formula:
- 60 km/h = 16.7 m/s;
- the coefficient of friction for dry asphalt and rubber is 0.5-0.8 (usually 0.7 is taken);
- g = 9.8 m/s.
We get the result - 20.25 meters.
It is clear that such a value can only be for ideal conditions: good quality tires and brakes everything is fine, you braked with one sharp press and all the wheels, while not going into a skid and not losing control.
You can double-check the result using another formula:
S \u003d Ke * V * V / (254 * Fc) (Ke - braking coefficient, for passenger cars it equals one; Фс - adhesion coefficient with coating - 0.7 for asphalt).
IN this formula put the speed in kilometers per hour.
We get:
- (1*60*60)/(254*0.7) = 20.25 meters.
Thus, the length of the braking distance on dry pavement for passenger cars moving at a speed of 60 km / h, under ideal conditions, is at least 20 meters. And that's with hard braking.
Wet asphalt, ice, rolled snow
Knowing the coefficients of adhesion to the road surface, you can easily determine the length of the braking distance under various conditions.
Odds:
- 0.7 - dry asphalt;
- 0.4 - wet asphalt;
- 0.2 - packed snow;
- 0.1 - ice.
Substituting these data into the formulas, we obtain the following values for the length of the stopping distance when braking at 60 km/h:
- 35.4 meters on wet pavement;
- 70.8 - on packed snow;
- 141.6 - on ice.
That is, on ice, the length of the braking distance increases by 7 times. By the way, on our website there are articles about that, and. Also, safety during this period depends on right choice winter tires.
If you are not a fan of formulas, then on the net you can find simple calculators stopping distance, whose algorithms are based on these formulas.
Stopping distance with ABS
home ABS task- do not let the car go into an uncontrolled skid. The principle of operation of this system is similar to the principle of stepped braking - the wheels are not completely blocked and thus the driver retains the ability to drive the car.
Numerous tests show that with ABS brake shorter way to:
- dry asphalt;
- wet asphalt;
- rolled gravel;
- on the plastic sheet.
On snow, ice, or muddy soil and clay, braking performance with ABS is somewhat reduced. But at the same time, the driver manages to maintain control. It is also worth noting that the length of the braking distance largely depends on the settings of the ABS and the presence of EBD (brake force distribution system).
In short, the fact that you have ABS does not give you an advantage in winter time. The length of the braking distance can be 15-30 meters longer, but then you do not lose control of the car and it does not deviate from its route. And on the ice, this fact means a lot.
Braking distances motorcycle
Learning how to properly brake or slow down on a motorcycle is not an easy task. You can brake front, rear or both wheels at the same time, engine braking or skidding is also used. If you brake incorrectly high speed you can very easily lose your balance.
The braking distance for a motorcycle is also calculated using the above formulas and is for 60 km / h:
- dry asphalt - 23-32 meters;
- wet - 35-47;
- snow, mud - 70-94;
- black ice - 94-128 meters.
The second digit is the skid braking distance.
Any driver or motorcyclist should know the approximate stopping distance of their vehicle when different speeds. When registering an accident, traffic police officers can determine the speed at which the car was moving along the length of the skid.
Which car has more stopping distance - loaded to the eyeballs or empty?
More than half of the people will answer that they have a loaded one.
And how are things really?
To begin with, you will have to plunge into the "wonderful school years", namely, into physics for the 6th grade. Section "Friction forces". We will not dive deep, ankle-deep.
So, let's look at the picture. Before us is one-eyed Billy Bones driving a Volkswagen. He saw something on the road and slowed down with might and main. From the point of view of physics, and Volkswagen, and Billy Bones - all this together is called a "body". Forces act on this body. This is the force of gravity that pushes the body to the ground. mg, support reaction force N which opposes it. These forces in the simplest case, on a horizontal surface, are equal and directed in different sides, and their resultant is zero. In addition to them, another force acts on a moving body - the force of friction Ftr. The friction force depends on the reaction force of the support and the coefficient of friction, it is directly proportional to them. More precisely, it is simply equal to their product: F tr. = μN.
But the reaction force of the support is equal to the mass of the body multiplied by the free fall acceleration g: N=mg.
Substitute the value N into the friction force formula:
F tr. = μmg
Since the acceleration of free fall is the same on the entire planet Earth, we conclude that the friction force depends on the coefficient of friction and body mass, and nothing else.
If some force acts on the matter, it starts to accelerate (recall that from the point of view of physics, deceleration is also acceleration, only with the opposite sign). According to Newton's second law, this force is equal to the product of mass and acceleration: F=ma
So the acceleration is a=F/m.
A single force acts on our body - the force of friction (the resultant of the rest is zero, which means they do not affect). Means,
a = F tr. /m, that is, acceleration (deceleration) is equal to the friction force divided by the mass of Billy Bones and his Volkswagen.
But the force of friction is F tr. = μmg. Substitute this value into our formula:
a = μmg/m. The mass divided by the same mass is reduced. Means, a = µg
So, acceleration (in our case, this is the intensity of braking) depends only on the coefficient of friction! Whatever the mass of the body, it is reduced with us, that is, the greater the mass, the greater the friction force, and exactly by the same amount.
Everything seems to be clear. But we need to solve the problem to the end and calculate the stopping distance. It's simple. Acceleration A equal to speed V divided by time t
a = V / t
Then
t = V / a = V / µg
According to the law of uniformly accelerated motion, the distance S equals:
S = at 2 / 2
Then
S = μg (V / μg) 2 / 2 = (V 2 / μg) / 2 = V 2 / 2μg
So,
The braking distance depends only on the speed and coefficient of friction, and does not depend on the mass of the car.
Well, since the acceleration of free fall is a constant value, and is equal to 9.81 m / s 2, then it can be simplified as follows:
S = V 2 / 20μ
So say the immutable laws of physics. But if you look at the characteristics of cars, it's easy to find that trucks have longer stopping distances than cars. It turns out that they violate these most immutable laws? Of course not. In order to understand this, you will have to go far beyond elementary physics and get acquainted in detail with the properties of braking systems (in particular, the difference in operation between "passenger" hydraulic and "cargo" pneumatic - and they are different), as well as in operation tires. In particular, depending on the coefficient of friction of the tire on its temperature, and, most importantly, on the moment at which the melting of the rubber begins. The sooner the tire starts to melt, the longer the braking distance will be. And before that, the tire that is pressed against the asphalt will begin to melt. That is - a truck tire.
However, in the very general case when the speeds are reasonable, the stopping distance specific car will not depend on how loaded it is. Do not believe those people who claim that a heavily loaded car has more. It is exactly the same as the empty one.
As for a car with a trailer not equipped with brakes, then by simple transformations we get the following acceleration formula:
a \u003d μg (1 + m pr. / m aut.)
From which it can be seen that the mass of the trailer itself does not matter, but only the ratio of the mass of the trailer to the mass of the car is important: the larger it is, the greater the acceleration and, therefore, the braking distance. It is directly proportional to the ratio of the masses of the car that brakes and the trailer that cannot brake. S \u003d V 2 / 2μg (1 + (m pr. / m auth.))
It can be seen that if the mass of the trailer is equal to half the mass of the car, then the braking distance will increase by half, that is, it will become one and a half times longer. And if the mass of the trailer is equal to the mass of the car, then twice.
The article was written based on lecture materials
When a novice driver gets behind the wheel, after two or three trips he is convinced of personal experience: stopping distance is not always the same. In some situations, this distance is vital, so everyone must be able to calculate the stopping distance of their car.
In theory, stopping distance is the distance traveled by a vehicle from the moment you press the brake pedal to a complete stop. This figure depends on several factors: speed, road surface, wear of the brake system, type of tires and their condition. To calculate the stopping distance, the formula S = Ke x V x V / (254 x Fc) is used. The designation S is the length of the braking distance in meters, Ke is the braking coefficient (y passenger car this indicator is equal to one), V is the speed at the beginning of braking (in km/h), Фc is the coefficient of adhesion to the road. The latter value depends on the weather: for dry asphalt it is 0.7, for wet asphalt - 0.4, for rolled snow - 0.2, and for ice - 0.1.
Do not forget that by depressing the brake pedal to the limit, you can completely block the wheels, then the car will become uncontrollable. Be careful on the road, observe moderate speed mode, and you can protect yourself, your passengers and other road users from traffic accidents.
People often listen to their feelings, and this is great! This is especially important in interpersonal relationships. But in relations with the "iron lady" intuition and sensations often deceive us. And one example: most drivers think that a heavy car has a longer stopping distance than a light one. It is a myth! Perhaps in some cases it is, but not at all because one car is heavy and the other is light :) The braking distance does not depend on the mass of the car! Surprised? I know :) And this is exactly what I want to write about today.
Origin of the myth
Where did the driver's stereotype come from, that the heavier the car, the longer the stopping distance? From practice, when we use service braking every day. We are used to driving alone, we are used to slowing down for so many meters in front of the same traffic light and pressing the pedal for so many centimeters. Then we fill the cabin with passengers, and the trunk with things, and at the same traffic light the car slows down worse, drives further.
Here is the root of the confusion: the car travels further with the same brake pedal movement that we are used to. It is able to stop as hard and with the same braking distance as in the case of a single driver in the cabin. Just to do this, you need to press the brake a little harder than the driver is used to. And this circuit will work until the ABS is activated - the limit of braking capabilities. Accordingly, the ABS will turn on both when empty and when complete car. Only to turn it on on a full car, you need to hit the pedal a little harder than is required on an empty car.
A few years ago, my friends and I got into a dispute on this topic, they tried to prove me wrong and, as confirmation, they cited the result of an experiment of 9th grade students from one of the Moscow schools. The guys took a Gazelle and investigated in practice the dependence of the braking distance and braking time of a school taxi car on the speed and mass. Understandably, in their experiment, a car loaded with people traveled further with each race than an empty one. Because the schoolchildren used regular braking and, apparently, compared the braking distance of the car with different loads with the same pressure on the brake pedal. If they braked urgently, by skidding, the braking distance would be the same in both cases. But emergency braking on a busy school street - it is extremely unsafe, and considerable skills are needed for this ...
What influences mass?
Vehicle weight affects tire and brake heat
First of all, the mass affects the heating of the tires and brake mechanisms. The greater the mass of the car, the greater the kinetic energy it has and the more work you need to apply the brakes to stop the car. But the margin of "strength" of any brakes is finite and is calculated by the manufacturer of any machine for normal operating conditions. If we take a Peugeot 107 and 10 times in a row on asphalt we slow down “to the floor”, accelerating it to top speed, then burn the brakes alive. Or if we throw bags of cement into the trunk and passenger compartment, and put a refrigerator on the roof, then theoretically the braking distance should not change. But standard brakes little Fawn are not designed for such a load of the car and, probably, they will not cope with the task - they will overheat. Because of this, the braking distance will increase.
So keep in mind, the weight of the car does not affect the stopping distance if the car is in good condition, used in the conditions for which it was created by the manufacturer, and loaded no more than allowed by the manufacturer. If you rape the car, the brakes may not withstand, and then not only the mass, but also the strength of the passengers' breathing will affect the braking distance :)))
Vehicle weight affects brake pedal feel
Mass also has a strong effect on braking properties cars. But it does not affect the length of the braking distance, but the sensitivity of the brake pedal and our feelings at the same time. The car does not care how many extra pounds it has loaded, it is in any case capable of the same emergency stopping distance, if the brakes hold out. And it is subjectively more difficult for the driver, because it is unusual to press harder on the pedal.
You can also say this: the braking distance of a loaded car increases in proportion to the mass with the same movement of the brake pedal. But the mass does not affect the limiting capabilities of the machine. And when you turn on the ABS, the same car, being empty or loaded, will go the same way to a stop. It is clear that we compare on the same road and start to slow down at the same speed.
Or the reverse situation: Armored Audi A8 weighing 3-4 tons accelerates to hundreds much faster than, say, Oka, which weighs 800 kilograms, probably. Heavier at times, and accelerates faster. Doesn't that surprise anyone??? Of course, everyone understands that the mass does not play the final role - put the engine more powerful and your mass will fly like a bullet. And braking is acceleration with a minus sign, and everything is the same here. Instead of a more powerful engine depress the brake pedal harder if the car gets heavier and the stopping distance doesn't change. And if it's even heavier - press even harder, if I'm even heavier - press even harder, there is no limit. Until the pads burn out :)
Practical confirmation
Of course, you can object to me that this is all theory, but in practice everything is different ... However, for several years now I have been conducting courses in emergency training for drivers and in practice I am convinced of the validity of what is written: The stopping distance of a car is independent of its mass.. In addition, in the following article there is a Bremstest video with an experiment on this topic, and you can see everything with your own eyes.
In the next article, the physics of braking will also be considered and I will scientifically substantiate that the mass and loading of the car does not affect the length of the braking distance.
Stopping distance is the distance it takes for a car to come to a complete stop from the moment the braking system starts working.
In everyday life, this term is often confused with stopping distance, but braking and stopping distances are different concepts. In the latter case, the distance that has elapsed since the driver realized the need to brake to a speed of 0 km/h is taken into account. The braking distance is part of the stopping distance. 
What does braking distance depend on?
The indicator under consideration is not a constant value and may vary for a number of reasons. All factors affecting the braking path can be divided into two large groups: driver-dependent and driver-independent. Among the reasons that do not depend on the person behind the wheel include:
- road condition;
- weather.
It is easy to guess that in rain, snow or ice, the distance it takes to stop a car will be greater than on dry pavement. Braking will be long and when driving on smooth asphalt, in which stone chips have not been added. Here, the wheels have nothing to catch on, unlike rough surfaces.
Note: It is worth noting that poor quality road (pits, potholes) does not increase the distance required to stop. Here the human factor plays a role. Trying to save the suspension, drivers rarely develop high speed on such roads. Accordingly, the braking path is minimal here.
Factors depending on the driver or car owner:
- the state of the brakes;
- system device;
- type of tires;
- vehicle load;
- movement speed.
The fact that the length of the braking distance of the car directly depends on the health of the braking system does not require proof. A car with a broken brake circuit or worn pads will never stop as quickly as a serviceable vehicle. 
A lot depends on the design of the brake units. Modern machines equipped with rear disc brakes and braking assistance systems, have much better grip with the road and a short braking segment.
In turn, the presence of EBD with ABS does not always contribute to reducing the distance required to stop. On dry hard surfaces, where wheel lockup occurs only under very heavy braking, the system really shortens the braking distance. However, on bare ice, "smart" electronic assistant begins to lose braking force even with light pressure on the brake pedal. At the same time, the car retains controllability, but its braking path increases significantly.
What determines the rate of deceleration? Of course, the type of tires. So, on bare, albeit frozen asphalt, as well as in snow porridge, the so-called. "Velcro" - winter tires not equipped with spikes. In turn, in ice and on snowy roads the most effective is studded "rubber".
An important factor influencing the size of the stopping distance is the speed and workload of the machine.
It is clear that a lightweight car at a speed of 60 km / h will stop faster than a truck loaded to capacity and moving at a speed of 80-100 km / h. The latter will not be allowed to stop quickly, too high for him speed and inertia.
When and how is freezing
Calculation of the braking distance may be required in the following cases:
- technical testing of the vehicle;
- checking the capabilities of the machine after finalizing the brakes;
- forensic examination.
As a rule, when calculating, the formula S \u003d Ke * V * V / (254 * Fs) is used. Here S is the stopping distance; Ke - braking coefficient; V₀ is the speed at the start of deceleration; Фс is the adhesion coefficient with the coating.
The coefficient of adhesion to the road varies depending on the condition of the pavement and is determined from the following table:
| Road condition | fs |
|---|---|
| Dry | 0.7 |
| Wet | 0.4 |
| Snow | 0.2 |
| Ice | 0.1 |
The Ke coefficient is a static value and is equal to one for all the most common passenger vehicles.
Example: how to calculate the stopping distance of a car when the speedometer shows 60 km/h in the rain? Given: speed 60 km/h, braking coefficient - 1, adhesion coefficient - 0.4. We consider: 1*60*60/(254*0.4). As a result, we get the figure 35.4, which is the length of the braking distance in meters.
The table shows how many meters the car will continue to move until it comes to a complete stop. It should be borne in mind that no other indicators are taken into account (turns, potholes on the road, oncoming traffic, etc.). It is doubtful that in real conditions on an icy road, a car will be able to slip a kilometer and not meet a pole or a bump stop.
| Speed | Dry | Rain | Snow | Ice |
|---|---|---|---|---|
| km/h | meters | |||
| 60 | 20,2 | 35,4 | 70,8 | 141,7 |
| 70 | 27,5 | 48,2 | 96,4 | 192,9 |
| 80 | 35,9 | 62,9 | 125,9 | 251,9 |
| 90 | 45,5 | 79,7 | 159,4 | 318,8 |
| 100 | 56,2 | 98,4 | 196,8 | 393,7 |
| 110 | 68 | 119 | 238,1 | 476,3 |
| 120 | 80,9 | 141,7 | 283,4 | 566,9 |
| 130 | 95 | 166,3 | 332,6 | 665,3 |
| 140 | 110,2 | 192,9 | 385,8 | 771,6 |
| 150 | 126,5 | 221,4 | 442,9 | 885,8 |
| 160 | 143,9 | 251,9 | 503,9 | 1007,8 |
| 170 | 162,5 | 284,4 | 568,8 | 1137,7 |
| 180 | 182,2 | 318,8 | 637,7 | 1275,5 |
| 190 | 203 | 355,3 | 710,6 | 1421,2 |
| 200 | 224,9 | 393,7 | 787,4 | 1574,8 |
We found an interesting calculator that not only calculates the indicator depending on the speed and road conditions, but also clearly shows the whole process. Located .
How to increase the intensity of the slowdown
From the foregoing, it became clear what is called the braking distance and what this indicator depends on. However, is it possible to reduce the distance required to stop the car? Maybe! There are two ways to do this - behavioral and technical. Ideally, if the driver combines both methods.
- Behavioral method - you can shorten the braking distance if you choose a low speed on slippery and wet roads, take into account the degree of workload of the car, correctly calculate the braking capabilities of the car depending on its condition and model year. So, the "Moskvich" of 1985 development will not be able to slow down as effectively as the modern " Hyundai Solaris”, not to mention more respectable and technologically advanced models.
- The technical method is a method of enhancing braking capabilities based on increasing the power of the braking system and using auxiliary mechanisms. Manufacturers of modern vehicles are actively using such methods to improve brakes, equipping their products anti-lock systems, braking assistance systems, using more efficient brake discs, pads.
It should be remembered that reducing the time required to stop is one of the ways to ensure the safety of the trip. Therefore, every driver must constantly monitor technical condition his " iron horse", in a timely manner to maintain and repair the braking system. In addition, it is important to choose the speed of movement taking into account the environment: time of day, road conditions, car model, and so on.
