With the continuous improvement of road conditions in China, especially the improvement of road grades, the vibration of vehicles caused by road surfaces is getting smaller and smaller. In order to further improve the comfort, safety and handling stability of the vehicle, more and more researchers have focused their research on the tires [1-6]. Tire uniformity refers to the ability of a tire to remain in a state of constant force under static or dynamic conditions. In order to ensure the safe driving of the vehicle, different parts of the tire have different functions, corresponding to different composition materials [3], using different processing equipment and processes, and finally these parts are attached and vulcanized into finished tires [7]. The tire material distribution cannot be absolutely uniform due to uneven tread and sidewall extrusion, uneven thickness of steel cord or fiber cord, uneven joint of the curtain, uneven lamination of the belt, and uneven vulcanization.

Car tire manufacturers at home and abroad use a uniformity test machine to check the uniformity of the tires, and determine the uniformity of the tires based on the test results. The uniformity test method has been standardized at present. Under normal circumstances, the tire factory is based on the tire uniformity index provided by the vehicle manufacturer as the standard, and the indicators provided by the vehicle manufacturer are mainly determined according to the vehicle structure and the highest speed. With the improvement of vehicle speed, safety, comfort and handling performance, the requirements for tire uniformity are getting higher and higher [2, 10].

Tire uniformity parameters are related to tire load, inflation pressure, specifications, brand, steering and other factors [11-12]. Different brands of tires have different trends in the uniformity parameters due to differences in manufacturing processes and structures, and the uniformity parameter design technology of well-known tire companies is the core technology of the enterprise and has been kept in a confidential state. Generally, the OEM will determine the tire uniformity parameters according to its own design experience, but after replacing the model and the tire supplier, it takes a lot of time and money to re-determine the tire uniformity parameters. Therefore, it is of great significance to compare the design rules of brand tire uniformity parameters with large market share at home and abroad and analyze the influence of typical factors on tire uniformity.

This work tests the relationship between car tire load, inflation pressure, specifications, brand, steering and uniformity parameters (processing and analysis of a large amount of sample data obtained by using a uniformity test machine) to provide guidance for tire design. .

First, the tire uniformity parameters and its influencing factors

1. 1 uniformity parameter
There are many objective parameters reflecting the uniformity of the tire, and some of the parameters that are widely used are defined as follows [13].

(1) Radial force deviation (RFV). It is the maximum fluctuation of the radial force of the loaded tire perpendicular to the running surface during one or more forward or reverse cycles at a fixed load radius and constant speed.

The impact of the RFV on the vehicle at low speeds is not obvious and can be neglected, but the impact on the vehicle at high speeds is highlighted. Sometimes there are only minor differences, but when the speed reaches a certain critical point, the steering wheel shakes, causing driver fatigue and poor ride comfort, and even noise and accelerated damage to the suspension components.

(2) Lateral force deviation (LFV). It is the fluctuation value of the lateral force that occurs repeatedly in the loaded tire at a fixed load radius and constant speed for one revolution per revolution.

LFV is generally caused by misalignment of the belt layer, uneven height on both sides of the bead curtain, uneven thickness on both sides of the sidewall, and uneven density of the cord. If the LFV exceeds the standard value, the vehicle will not be able to travel straight, and the wheel will swing to the left and right, affecting the steering stability and driving safety of the vehicle, and even causing the tire to be eccentric.

(3) Longitudinal force fluctuation (TFV). It is the fluctuation of the longitudinal force of the loaded tire at its fixed load radius and constant speed, which is repeated for one revolution per revolution.

TFV is more reflective of fluctuations in the longitudinal force of the tire at high speeds, mainly due to fluctuations in the natural frequency of the tire.

(4) Taper effect (CON). It refers to the lateral force offset that does not change the sign due to the change in the direction of rotation of the tire. CON is generally caused by improper bonding of the belt layer, uneven thickness of the underlying rubber at both ends of the belt layer, uneven thickness of the shoulders on both sides, and the like. Unevenness on both sides of the tire causes the tire to resemble a rolling cone as it rolls, usually with a taper force to characterize the CON. The influence of CON on the vehicle is similar to that of the LFV. If the CON is improperly controlled, the vehicle may be deflected.
CON=0. 5(LFD1+LFD2)

The LFD is a lateral force offset. When the tire is rotating forward, it is recorded as LFD1, and when it is reversed, it is recorded as LFD2.

(5) Angle effect (PLY). It refers to the change of the lateral force of the symbol as the direction of rotation of the tire changes.
PLY=0. 5(LFD1-LFD2)

PLY mainly reflects the structural design problems of the belt layer, such as the arrangement of the belt layer, the density of the belt layer cord, the uneven shear force when the belt layer is bent, and the uneven thickness of the belt layer. The impact of PLY on vehicle handling stability is similar to that of CON.