[Aika car shopping guide original]
"Putting on four new tires is like changing a car." From the industry to the public, there are many people who hold this view.
A piece of ring-shaped rubber, how can it be so powerful? Tires may seem inconspicuous, but they play an extremely important role. As the only part of the car in contact with the ground, the role of the tire is irreplaceable. As long as the car is moving, it is indispensable to the participation of tires. Tires are to cars as shoes are to people. A good pair of shoes, so that the owner can move and move. A good set of tires, let the car like a tiger.
From acceleration to braking, from handling to comfort, any driving-related performance is inseparable from the tires. The tires combine thousands of forces in one, which can be understood as the second set of suspension of the car. Unlike suspension, the mechanical properties of tires are more complex. If chassis tuning is metaphysics, then the tire is the master of metaphysics. Choose the ideal tire, the car can fully release its nature.
Talking about tires, we must also start from a "teaching accident". In the middle school physics textbook, there is such a formula: F = μN. The physics teacher told us that the friction force is related to the friction coefficient and the positive pressure of the contact surface, and has nothing to do with the contact area. From the first year of junior high school to high school, this law of physics constitutes the basic understanding of friction in children.
It wasn't until the teenagers grew up and touched the steering wheel with their own hands that they discovered the "mistakes" of junior high school physics. Old drivers often say that the wider the tire, the stronger the grip. According to the logic of junior high school physics that "friction has nothing to do with the contact area", this is obviously wrong. However, it turns out that the narrow tires are slippery and the wide tires are slimy. Where does truth stand? This brings us to the macro contact area and the micro contact area.
Key point: Friction depends on the microscopic contact area, and there is a positive correlation between the two. The correlation between friction and pressure is essentially derived from the change of microscopic contact area. When we increase the pressure, the macroscopic contact area (as seen with the naked eye) does not change, but the microscopic contact area gradually becomes larger, and the friction force also increases. Theory is inevitably a bit abstract, so let's take a common example in life. When we wash dishes, the tighter the sponge is pressed, the easier it is to wipe off the dirt, which is the power of the microscopic contact area.
The nonlinearity of tires sounds unpredictable and is actually everywhere. As long as the car runs, it will definitely encounter the corresponding scene. When the vehicle turns, the load (commonly known as the "center of gravity") moves outward, and the body rolls. At this point, there is more load on the outside and less load on the inside, and the outer wheels provide more lateral force. For the same car, the more load is added, the lower the marginal grip. Controlling load transfer can reduce the drawbacks of tire nonlinearity, thereby improving grip overall.
The "mistake" of junior high school physics
In chassis tuning, the most important thing is the shock absorber and all kinds of rubber, and the tire is undoubtedly the "glue king" in the rubber parts. Tires play a crucial role in both handling and comfort. If the tires are not perfectly matched, even the best suspension will not be able to perfectly reflect the value. During the chassis development phase, engineers need to combine chassis design and tuning style to select the right tire, a process known as tire selection. In repeated deliberations, if the suspension adjustment is greatly adjusted, the tire selection should also be re-implemented.
The role of the tires is not limited to handling, but also in terms of comfort. Faced with potholes, the tires completed the first layer of filtration, making the original stiff bumps soft. With stiff tires, the suspension will withstand greater shocks, and there are differences in the speed of shock absorber movement (and the corresponding damping). In a way, the tire-suspension relationship is more like multiplication than addition.
For comfort, tires are not as soft as possible. For sport, tires are not as hard as possible. Tire formulations should not be biased, but should adhere to the principle of moderation. For example, tires with good support and toughness tend to have a more advanced feel than tires that are soft. At the moment the tire touches the pothole, passengers can predict the next impact amplitude and impact process.
Tires: The second in charge of the chassis
There is no doubt that tyres are of great importance to dynamic performance, with handling, comfort, economy and NVH performance all affected by them. The so-called "changing tires is like changing cars" is actually not an exaggeration. Is it necessary to choose the original tire? How big are the differences between different tires? What are the advantages and disadvantages of explosion-proof tires? Next, let's set aside the theory and focus on examples.
Nowadays, the vast majority of mature car companies will customize special tires for special vehicles according to the characteristics of the vehicle. Some brands also print certified labels on tires, such as Porsche N logo, BMW star logo, Mercedes-Benz MO, Audi AO. In addition, hyundai N, Alpina and other high-performance sub-brands also have independent certification marks, writing the sports gene on the "shoes".
Original tires are custom-developed for the supporting model and are often referred to as OE (original equipment) tires. OE tires are not only available for new cars, but can also be purchased later. The opposite of OE tires is the RE (replacement equipment) tire, which is an aftermarket replacement tire that has not been custom developed.
There is no perfection in the world. In general, tires have a relatively fixed performance ceiling, requiring engineers to choose between comfort and movement. BMW Star-Label tires focus on handling, but at the expense of comfort and tranquility. Mercedes-Benz MO tires focus on comfort, and handling is difficult to do to the extreme. For example, the recently tested EQS 450+ has excellent NVH quality, and the filtering and energy consumption are also very good, but the brake performance (100-0km/h 39.61m) is a big surprise.
There is nothing wrong with the RE tire itself, what is wrong is the matching of the tire to the vehicle. For models with delicate original tuning, replacing the RE tire often destroys the steering characteristics, resulting in a more obvious "push head" or "tail fling". Some RE tires are slow to respond to steering, and there is less pleasure in cutting butter with a hot knife. If you use a re tire with weak performance, it is also possible to reduce both comfort and handling. Choose the OE tire and you will get the complete chassis style that the engineer wants to express. Choosing a RE tire increases uncertainty, but it also offers the opportunity to revolutionize the experience. If you know exactly what you want, re-fetals are also a rational choice.
Editor's Comments:
As China's auto market moves into deep waters, new car sales have become lackluster, and the aftermarket has become a new growth point. In recent years, more and more car owners have begun to try modifications. Among them, the most popular substantive modifications are nothing more than three: power, exhaust, and vibration damping. In contrast, tire upgrades (or replacements) are not taken seriously, and it is not uncommon for "good cars with bad tires" to happen. The tire looks like just a piece of rubber, but it is one of the most important chassis components. Planning to change or change your car? Try changing tires and maybe you'll find a surprise.
In the coming period, we plan to launch a series of tire selections. If you have a tire model or test content that interests you, you may wish to leave a comment in the comments section. We will plan the follow-up content according to the opinions and suggestions of readers and friends.
Should I choose the original tire?