Whether you are taking the national highway or running on the high speed, you will often encounter a lot of large trucks, especially on the national highways around the city, there are a lot of large trucks. Attentive friends will observe such a phenomenon, many large trucks when the brakes are applied, the rear tire will smoke, and the ground will grind a black mark, especially when the car is empty. Cars, on the other hand, rarely have smoke from their tires when braking. What's going on?
In fact, when braking, the tires smoke, which is caused by the friction between the tires and the ground, and the friction will produce high temperatures, resulting in high temperature and smoke from the tire rubber, which will also leave black marks on the ground. The main reason is that the rear wheel of the car does not have ABS, or the brakes have been modified, and the ABS no longer works. The brakes of the big car are air brakes, the braking force is very large, the rear wheels do not have ABS, if the vehicle is empty at this time, the weight is light, the wheels are easy to lock. After locking, it is equivalent to sliding friction, and the contact point between the tire and the ground remains unchanged, and it has been worn out at that point. A large amount of heat will be generated quickly, causing the tire to smoke, and the rubber of the tire to fall off, leaving a mark. It's like if you let a ball move a certain distance and drag it in your pocket is more worn out than if you let it roll, and the sliding friction is greater than the rolling friction.
The next thing we need to know is what ABS does. It is a system to prevent the wheels from locking, so that the tires are in a state of rolling and sliding at the same time, that is, they are always on the verge of locking, but they are not locked. ABS sensors are installed at each wheel, which can sense whether the tires are rotating or not, and then determine the status of the wheels through a comprehensive analysis of signals such as vehicle speed. When the wheels are about to lock, the ABS pump will work and automatically release the braking force. At this point, the driver's feet will feel like they are being rebounded, and the braking force will seem to be weakened.
In fact, the real braking force is not weak, many people think that letting the tires lock the braking force is the maximum, but in fact, this is not right. The optimal state of braking force is between the critical state between complete locking and rolling, and the principle that the maximum static friction is greater than the sliding friction force is used to keep the tire in a state of maximum static friction. This braking effect is the best, the shortest braking distance, especially on the slippery road, the intervention of ABS can greatly shorten the braking distance, the more slippery the road, the driver himself can feel the role of ABS.
The reason why the wheels are locked almost can't be seen in the car is because all the cars are equipped with ABS, and no one will take the initiative to modify and dismantle. With the intervention of ABS, the wheels will not lock. Slippery while rolling has little friction on the tires and is uniform, so you can't see the tires smoking when braking. In addition to making the braking distance shorter, it can also greatly extend the service life of the tires. If the tire is grinding and smoking, then a large number of rubber particles will fall off at this point, and the black mark on the ground is the tire rubber. If there is a lot of smoke, it must be severely worn at multiple points, and the life of the tire will be greatly reduced. Of course, the main role of ABS is not this, in order to prevent the vehicle from flicking or uncontrollable direction when braking suddenly. If the rear wheel is locked, there is a high possibility of tail flicking, and if the front wheel is locked, it is impossible to dodge in the direction. If it is not locked, there will be no such safety hazards, neither tail flicking, but also controlled direction.
In addition to the smoke emitted by the brakes, the large trucks we see on the highway, even if they do not brake, why do the tires keep smoking? In fact, it is the water vapor formed by the brake pads being sprayed with water and evaporating at high temperatures. Due to the heavy load of the car, the braking force also needs to be very large, otherwise the car will not be able to brake. The braking mode of large cars is drum brake, and the disadvantage of drum brake is that it is easy to high temperature. Because when braking, due to the friction of the brake pads, a high temperature will be generated, and the drum brake is wrapped very tightly, and the heat is not easy to dissipate, and a high temperature will be formed. If the temperature is too high, the brakes will fail. Therefore, water sprinklers are installed at the brake pads of the cart to cool down the brakes and prevent the brake temperature from being too high.
On highways with many mountain roads, many service areas have cooling pools, one filled with water, and large trucks can slowly drive over to cool the tires and brakes to ensure that the brakes do not overheat. Therefore, if you see that the tires have been steaming while driving, it means that the car is fully loaded. If it is not an emergency brake, the rear wheels of the car are also smoking, indicating that the car is empty. On the downhill section, you must not walk in front of the big car, although its braking system is more powerful, there is also greater instability. If you see smoke coming from the brakes of a large car or bellowing air while driving, try to stay away from them as much as possible to minimize the safety hazards that you can predict.