As the temperature continues to drop, more and more car owners are beginning to consider replacing winter tires. Car owners who do not plan to replace their tires also need to adjust their tire pressure; low temperatures will increase the hardness of ordinary tires, resulting in a decrease in tire grip. Therefore, although low temperatures will reduce tire pressure, it is recommended to lower the tire pressure appropriately than the recommended value when inflating.
While we were doing science popularization and discussing with readers, two questioning comments appeared.
One is whether the width and pressure of the tires affect friction, and the other is whether it is necessary to replace winter tires.
Let’s first explain the first question, and the second question will be explained in a separate article.
Does tire width affect friction
Correct answer:
It does not.
Most car enthusiasts believe that the width of the tire will affect friction. However, this is a wrong view. There are two factors that determine friction; the first factor is the "roughness" of the contact surface of the object, and the second is The weight of the object. In short, the rougher the crown of the tire (the surface in contact with the ground), the greater the friction. For example, if you hold down a piece of 200-grit sandpaper and slide it on the table, you will need to use more force in the process. It feels obviously laborious; but if you change to a piece of 2000-grit sandpaper, it will feel much easier. The reason is that the surface of 200-grit sandpaper is rougher than 2000-grit sandpaper.
But as long as you apply enough force to the 2000-grit sandpaper, the friction speed will be the same.
’s correct conclusion is that the width of the tire does not affect friction, so you need to pay attention to the tread pattern when choosing tires.
The tread pattern of road tires (HT) is interwoven horizontally and vertically. The function of the horizontal pattern is to improve the grip of the wheel on dry roads, and the function of the vertical pattern is to improve the drainage performance of the tire; when driving on rainy days, the vehicle travels for one kilometer. , the tires can throw out several kilograms of rainwater. On the contrary, if there is no reasonable longitudinal pattern design, the drainage performance of the tire will be very poor, and it will be easy to slip when driving in rainy days. However, most tires have horizontal and vertical interwoven patterns. Only AT/MT tires are special. AT is an all-terrain tire and MT is a mud-terrain tire. These two tires are mainly used for both off-road or pure off-road use; use these Vehicles with two types of tires should pay special attention when driving on rainy days. The speed should not be too fast and the braking distance should be appropriately extended.
Tire width must affect grip
The author did not say that tire width is one of the factors that affects friction. It is just that some readers understand "grip" as "friction" or confuse the two concepts.
There are three factors that affect wheel grip. The first two are factors that determine friction, and the third is the width of the tire.
Grip is not the same concept as friction in tire science. When discussing grip, we must talk about "deformation"; tires that rotate at high speed will deform slightly, and of course the crown will also have it. The rubber of the crown is deforming. During the process of contact with the ground, an active force will be generated, which can be understood as grip.
Tires of different widths will of course have different amounts of deformation. Car companies can be smart. The manufacturing cost of wide tires is high, and the selling price is also high. If wide tires are meaningless, if large wheels and tires are used just for good looks. , then the wheel hub can be made very narrow, as long as the diameter is large enough. On the contrary, when car companies use large wheels and wide tires regardless of cost, it means that the width of the tires must be related to vehicle handling and braking performance.
wide tires provide greater deformation, which can improve grip during acceleration and braking, effectively avoid slipping during acceleration, and can also effectively shorten braking distances.
Properly lowering the tire pressure can improve the grip. Excessive tire pressure will prop up the middle of the wheel and reduce the contact area between the tire crown and the ground. Therefore, excessive tire pressure will inevitably reduce the tire grip and easily cause Skidding during rapid acceleration will inevitably extend the braking distance.
On the contrary, slightly lowering the tire pressure can allow more areas of the tire crown to contact the ground, making it less likely to slip when accelerating, and the braking distance can be shorter; of course, a large contact area will also increase the wear area of the tire crown and However, excessive tire pressure will also cause eccentric tire wear. Whichever of the two is better, lower tire pressure is better because the wear is more balanced.
Finally, let’s talk about the knowledge about tire eccentric wear. Even if the tire pressure is reasonable, there will be slight eccentric wear. Only by lowering the tire pressure appropriately can it be balanced; the wheels are not 90 degrees perpendicular to the ground. Interested students can take a look. Looking at the cars on the roadside, most of the wheels are upward and inward, which means they are generally a little "outward". Since the car will generate lateral forces when turning, the wheel design with a certain inclination angle can effectively interact with the lateral forces; if it is a 90-degree standard vertical angle, the wheels will tilt outward to a large extent when turning, like The ankle before the sprain was normal.
Therefore, it is necessary to appropriately lower the tire pressure in winter. Lower tire pressure is always better than higher tire pressure.
Editor: Tianhe Auto-Automotive Science Island, published by Tianhe MCN, welcome to like and comment
