Durability, service life, tire terminology, small science

- Jul 04, 2019-

Recently, the Beijing Consumers Association announced the comparison test results of 26 tire samples from 13 brands. The results show that all samples meet the requirements of national standards, but some media have interpreted the "durability and low pressure" test errors as tire wear tests. . The test of tire service life requires continuous operation at a certain speed on selected road conditions. This test is a "durable and low air pressure" test for tires, which is aimed at the fatigue resistance of the tire and the reliability of the tire at low air pressure. To this end, we have compiled and summarized six tire-specific terms for your reference.


1, tire outer edge size


The outer diameter of the tire refers to the outer dimensions such as the outer circumference and the total width of the tire measured when the tire is mounted on a predetermined rim and inflated to a predetermined pressure. The outer diameter and the total width can have a certain range of fluctuations within the limits allowed by national standards. For tires of the same specification and different brands, the detection values of the outer diameter and the total width can be in the vicinity of the minimum value or near the maximum value, and the difference is a few millimeters and more than ten millimeters.


For consumers, when buying replacement tires for their cars, you can't just look at the same specifications. Try to choose the same brand of tires so that the tires can be more consistent in size. For the two tires on the coaxial, the pattern must be the same, otherwise, the vehicle may be biased or even out of control when braking.


2, tire strength


The tires are subjected to the oscillating and accidental impact of the complex road during driving, and the tire strength test is to evaluate the structural performance of the tire against impact by detecting the energy required for the steel indenter to press through the tire carcass. During the test, a standard diameter hemispherical cylindrical metal indenter is pressed into the tire at a specified speed until the tire crown is pressed through, or the minimum breaking energy specified by the standard is reached, or the indenter touches the rim to the tire carcass structure. The damage energy value indicates its strength. The greater the detected value of the tire damage energy, the better the impact resistance performance of the tire carcass structure.


3, tire ring resistance


When the car turns, it will generate centrifugal force. When the centrifugal force exceeds the force between the tire bead and the rim, the bead will leave the edge of the rim and make lateral displacement inward on the bead seat of the rim. If the tubeless tire bead is disengaged from the rim, the air inside the tire quickly leaks from there, and the air pressure drops rapidly, which may cause the vehicle to lose control. The knock-off resistance test is a static simulation test performed on an indoor test machine based on actual use conditions, that is, applying a lateral force to the tire sidewall, forcing the bead to be disengaged inward from the bead seat of the rim, and determining the maximum required. The force value, which is the drag-off resistance of the tire. The greater the detected value of the tire's tripping resistance, the greater the force required to remove the tire bead from the rim, and the more difficult the tire is to be detached from the rim when the tire is turning.


4, tire durability and low pressure


A tire is a composite structural article composed of multiple materials and multiple components that is used under severe and complex conditions. During the running of the tire, the ground friction is severely rubbed with the ground, and at the same time, various stress and strain will be generated in each part. These stress strains are alternately changed at a relatively high frequency, resulting in fatigue of the tire, and shearing force is generated during use of each component. In addition, due to the elastic hysteresis, the tire converts part of the kinetic energy into heat energy during the process of endurance, so that the tire works at a higher temperature. The tire itself is a poor conductor of heat, it is not easy to dissipate heat, and it is easy to cause thermal oxygen aging of the rubber. Therefore, the heat resistance and fatigue resistance of the tire are important factors determining the service life of the tire, and the durability test is an internationally recognized tire resistance test. An important means of heat and fatigue resistance. The endurance test is to use the drum as the active simulated road surface. In a certain temperature range, the combination of the tire and the rim filled with the predetermined air pressure is pressed on the drum according to the specified load, and the drum is operated at a constant speed.


The low air pressure test is to reduce the air pressure to 140 kPa or 160 kPa after the endurance test is completed, and maintain the same speed and load rate for 1.5 hours, mainly to evaluate the durability of the tire under lower air pressure conditions. The longer the cumulative inspection time under the same test conditions, the better the fatigue and heat resistance of the tire.


5, tire high speed


The high-speed performance test is to evaluate the high-speed running performance of the tire according to the tire speed symbol. The high-speed performance test of the tire is to use the drum as the active simulated road surface. In a certain temperature range, the combination of the tire and the rim that is filled with the specified air pressure is pressed on the drum according to the specified load, and the test speed of the drum is gradually increased. Until the tire is damaged or reaches the specified speed.


If it exceeds the standard maximum speed of 10 kilometers and exceeds the standard 1st gear, the higher the number of gears exceeding the standard speed, the better the high-speed performance of the tire.


6, tire rolling resistance


During the running of the vehicle, the tire is deformed by contact with the road surface. Due to the viscoelastic property of the rubber material, a part of the energy loss is caused. The energy loss of the tire unit mileage is the rolling resistance of the tire that we usually talk about. The smaller the detection value of the rolling resistance is, the better.