2. 1 Working principle
The uniformity testing machine is currently one of the most common devices for detecting tire unevenness [14]. Tire uniformity measurement is carried out under the condition of rotating tire loading. The test tire is mounted on the main shaft of the testing machine. During the measurement, the main shaft and the rotating drum are kept stationary by the mechanical support, and the axial positions are parallel to each other. The drum simulates the ground and gives test. The tire exerts a certain load, which is equivalent to the pressure exerted by the ground on the tire during the running of the tire. The vibration during the rotation of the tire is transmitted to the drum and transmitted to the multiphase load cell fixed at both ends of the drum. When the distance between the spindle axis and the drum axis is stabilized, the load encoder and the rotary encoder at the bottom of the spindle can measure the periodic changes of the tire's RFV, LFV and TFV, and calculate CON and PLY.

2. 2 basic parameters
The test was carried out using a HSU 5.3 high-speed uniformity tester (see Figure 1) produced by ZF, Germany. The drum parameters are: diameter 2000mm, surface beat 0. 02mm, drum width 550mm, balance level 2.5, maximum speed 300km·h-1. The equipment capacity is: loading maximum force 20kN, measurement accuracy error ± 5%. Sensor test capability: radial force ±15kN, lateral force ±10kN, tangential force ±15kN, positive return torque ±4000N·m, overturning moment ±4000N·m. The tester can be used for light load and load radial tire uniformity testing. The testable tire parameters are: rim diameter 330. 2 ~ 635. 0mm (13 ~ 25 inches), outer diameter 500 ~ 1000mm, section width 120 ~ 400mm, rolling radius 240 ~ 500mm.

Third, the tire uniformity test

3. 1 test object
Select 6 brand car tires with a large domestic market share, and test the tire uniformity parameters RFV, LFV, TFV, CON and PLY under low-speed motion with changes in tire load, inflation pressure, specifications, brand, etc. fluctuation.

Test subjects: The tire specifications were 195/65R15, 205/55R16 and 225/65R17. Recorded as A tire (brand 1 product, 195/65R15), B tire (brand 1 product, 205/55R16), C tire (brand 1 product, 225/65R17), D tire (brand 2 product, 205/55R16) , E tire (brand 3 product, 205/55R16), F tire (brand 4 product, 205/55R16).

3. 2 test conditions
(1) Test load. The RFV, LFV, TFV, CON and PLY of the tires were tested at 70%, 80%, 90% and 100% load with a load of 650 kg at 100%.

(2) Inflation pressure. The RFV, LFV, TFV, CON and PLY of the tires were tested at inflation pressures of 180, 200, 220, 240, 260, 280, 300, 320 and 340 kPa, respectively.

3. 3 Test methods
Before the start of the test, the tire is inflated according to the regulations. After the pneumatic tire is allowed to stand at room temperature for 3 h, check whether the inflation pressure reaches the specified value. When the test is completed, the test is carried out: the tire is mounted on the test machine, and the test drum is moved to the tire. Pressing close together until the specified load is reached; the tire starts at 400 r·min-1 and then falls to 60 r·min-1 for constant speed rotation; first, clockwise rotation test, then counterclockwise rotation test, test item For RFV, LFV, TFV, CON and PLY; finally the test tire and drum are removed from the test machine spindle [14].