Tire selection and use

Tire is one of the most important components in the automobile driving mechanism, and it is directly related to the safety and operating economy of the vehicle. If the tires cannot be properly selected and used, not only will the performance of the car be reduced, but it will also affect the driving safety of the car, and it will even cause unnecessary casualties and property damage. Especially for the cost of using the vehicle, the tire is the largest consumption other than fuel consumption. If the tire cannot be properly selected, used, and maintained, not only will the user not create the desired economic benefits, it will bring The heavy economic burden makes users miserable.

1 Basic principles of tire selection

The basic principle of tire selection: First, the tire load capacity and speed grade are calculated according to the axle load to determine the specifications of the tire. This relates to the performance index and driving safety of the vehicle. Second, according to the structural characteristics of the vehicle (such as tractors, dump trucks, mixers, etc.), road conditions, climate, etc. determine the tire structure (tire or ordinary tire) and tire patterns to meet the passing of the vehicle, smooth running The interchangeability of the tires, steering characteristics, etc., and the convenience of the tires, and the ease of maintenance, etc., are required, and the economy is estimated. Finally, consider other auxiliary requirements for tires, such as the stability of tire sources and vehicle management issues.

1.1 Rated load

When selecting a tire, it must first be ensured that the tire cannot be overloaded. If the tire is overloaded, not only will the tire wear abnormally, it will cause a drastic shortening of the life span, and sometimes it will cause the tire's rigidity and the deterioration of the adhesion performance due to the overload of the tire, which will seriously affect the driving stability of the vehicle, even when the vehicle is running. A burst puncture resulted in the destruction of the car. For the same specifications of the tire may have different load capacity, the following matters must be taken into account when selecting:

a. tires of the same specification have different structural layers, so the load capacity is also different and must be carefully selected.

b. The allowable load of the tire of the same specification is different when the single tire is used and the twin tire is assembled. When the twins are installed together, the load on the inside and outside tires is not the same due to the crown of the road and the bending deformation after loading the axles. At this time, the sum of the carrying capacity of the two tires is about 1.72 times that of the single tire, not twice relationship.

c. In service vehicles, the principle of secondary tire selection is that the load capacity of the tires is not high, and the front and rear axles must be taken into consideration.

1.2 Determination of speed grade

The tires of the same specification not only have different load capacities, but also have different speed grades. Sometimes the tire load of the vehicle is not overloaded. However, the speed may be overloaded, which may also cause problems such as excessive heat generation, excessive wear and puncture of tires, and tire speed. Overloading may cause the following phenomena:

a. Tyre overheating can cause excessive wear or even puncture.

b. When the vehicle is running, if the tire speed is overloaded to a certain degree, the tire's inherent vibration frequency caused by the external force and the tire's natural vibration frequency are equal, the tire itself will resonate, generating a "standing wave." Once the phenomenon of "standing wave" occurs, the annual vehicle will experience severe jitters, and the tire will burst due to a sharp rise in temperature. This is the most dangerous situation.

c. When the vehicle runs on a road with accumulated water, if it reaches a certain speed, a “lubricant film” like a sliding bearing will appear between the tire and the ground, and the vehicle in motion will be like a hovercraft floating on the water. This phenomenon is called "water mat effect." When this happens, the adhesion between the tire and the ground decreases sharply. Once external force is applied, the vehicle immediately deviates from the normal driving trajectory, and flicking occurs when the weight is low, and the person flees.

d. When the vehicle reaches a certain speed, if the tire balance accuracy is not enough, it will cause excessive wear of the steering wheel hemp and tires. Low-speed tires have low dynamic balance and this phenomenon often occurs at high speeds. Different speed grade tires have different dynamic balance accuracy.
For ordinary tires, the speed grade is generally below the maximum speed of 90km/h (heavy truck tires allow the maximum speed of 70km/h or less). The maximum speed refers to the vehicle's continuous speed, not the average speed, and the maximum duration of continuous driving is 1 h. Heavy-duty vehicles equipped with ordinary tires are not suitable for high-speed driving on highways. Radial tires should be used. However, radial tires of the same type also have different speed grade specifications (S0 ~190km/h). Therefore, the radial tire must be selected according to the speed of the vehicle.

1.3 Mechanical properties of the tire

The mechanical properties of the tire are also important performance indicators of the tire, mainly referring to the tire's passing performance, cushioning properties and stiffness.

a. Through performance

The passing performance of a tire mainly refers to two aspects. On the one hand, the smaller the diameter of the tire is, the smaller the obstacle ability of the vehicle is, so the different diameters of the tires are selected for different vehicles to ensure the obstacle-resistance performance of the vehicle; on the other hand, when When the vehicle is driving on muddy and icy roads, the adhesion between the tire and the ground is reduced, and sufficient driving force cannot be provided to ensure the normal passage and effective braking of the vehicle. Therefore, the tire must have a reasonable structure such as tire diameter and width. And patterns and so on.

b. If the stiffness of the tire is not enough when turning the vehicle (which is often referred to as "fetal softness"), the tire's adhesion performance immediately deteriorates, and the vehicle will appear understeer and deviate from the normal running track. This is the case when driving at high speeds. Danger. In general, the wide tire has a large stiffness and the standard tire has a small stiffness.

c. The tire must have good cushioning properties, and absorb and buffer the vibration of the vehicle together with the suspension. If the tire cushioning performance is not good, it will affect the riding comfort of the vehicle and also affect the life of other parts of the vehicle.

1.4 Noise

There will be noise during the tire driving. The tires with different structures and different patterns will have different noise levels at different vehicle speeds. Sometimes the noise will be annoying.

2 Other issues to consider

a. When twin tires are installed on the same shaft, old and new tires cannot be mixed. The new tires have a large diameter and the old ones have small diameters. As a result, the new tires will be heavily overloaded, old tires will be underloaded, and new and old tires will wear unevenly.

b. When the twin tires are installed on the same axle, they cannot be loaded with tires of different specifications. Different diameter tires of different specifications, large diameter overloads, and small diameter underloads will also cause uneven wear of the tires.

c. The tire with the same pattern must be installed on the same axis. Otherwise, the adhesion of the tire on both sides of the same axis will be different. Therefore, the braking force on both sides of the tire has a large deviation and the braking deviation is likely to occur.

d. No retreaded tires can be installed on the steering shaft. Due to the poor adhesion between the retread floor and the old carcass, it is very easy for the vehicle to skim off the retread when turning and lose its steering function. In addition, plies of old tires often have flaws and are prone to punctures, so they cannot be mounted on steering shafts.

In short, the selection and use of tires must be considered comprehensively based on the vehicle's load, speed, road conditions, and climate conditions in order to ensure the safety and economy of vehicle travel.