GB/T 33829-2017Test method for snow grip performance of passenger car tyres (English PDF)

3.1 Candidate tyre

The tyre that is measured through the test.

3.2 Standard reference test tyre; SRTT

Standard reference test tyre A set of special candidate tyres that are used as a reference in the measurement system. To minimize the variation, these tyres which have tightly controlled design characteristics, are produced, controlled and stored according to relevant standards.

3.3 Control tyre

The tyre that -- If the candidate tyre and the standard tyre cannot be directly compared on the same vehicle, THEN, compare the tyre with the candidate tyre,

4.2.2 Climatic conditions

The ambient temperature range which is measured at about 1 m above the ground is -21°C ~ -7°C;

The snow temperature which is measured at a depth of about 1 cm from the snowy road surface shall be -21°C ~ -9°C; The temperature variation during the test shall not exceed 10°C.

During the test, large variation in direct sunlight and humidity shall be avoided; the wind speed should not exceed 5 m/s.

4.2.3 Test vehicle conditions

4.2.3.1 Select an ABS-equipped test vehicle to which both the candidate tyre and the standard tyre are applicable.

4.2.3.2 The test vehicle shall be equipped with a calibrated sensor suitable for winter measurements. The speed and distance data acquisition system shall be equipped with a function to store measurement results. The sensor and system accuracy shall meet the requirement that the relative uncertainty of the measured or calculated mean fully developed deceleration is less than 1%.

4.3 Test measurement instrument

4.3.1 Test measurement instruments shall be insensitive to vibration, deceleration and ambient temperature changes. All the exposed parts shall be able to withstand 100% relative humidity, dust, shock, vibration and other unfavorable factors.

4.3.2 The speed of the test vehicle shall be measured by a non-contact speed measurement instrument such as a five-wheeled instrument or a global positioning system (GPS). In the range of ambient temperature of -21°C ~ -7°C, the allowable error:

a) Vehicle speed measurement: ± 1% or ± 0.5 km/h, whichever is larger;

b) Distance measurement: ± 0.1 m.

4.3.3 During the test, the vehicle shall display the actual vehicle speed measured by measurement-instrument OR the difference BETWEEN the actual vehicle speed AND the standard vehicle speed, so that the driver can adjust the vehicle speed.

4.3.4 The accuracy of the barometer shall be ± 5 kPa.

4.7 Adopt control tyre to test the snow performance

4.7.1 Overview

If the candidate tyre and the standard tyre differ greatly on specifications, and cannot be directly compared on the same vehicle, then, use candidate tyres to perform comparison test respectively.

4.7.2 Principle

Use control tyres and two different test vehicles to perform comparison tests with the candidate tyres respectively. One of the test vehicles is suitable for the assembly of the standard tyre and the control tyre; the other is suitable for the assembly of the candidate tyre and the control tyre. The former is used to measure the standard tyre and the control tyre, and the latter is used to measure the candidate tyre and the control tyre. The two vehicles shall be tested on the same road surface; the surface temperature difference between the two tests shall be within 5°C. Two test vehicles shall use the same set of four control tyres which shall be mounted on the same position. The environmental conditions shall be comparable; all tests shall be completed within the same day.

Calculate the snow grip index SG of the candidate tyre relative to the standard tyre according to Formula (10):

Where:

SG1 -- relative index of the control tyre and the standard tyre;

A.1 Conditions of use

A.1.1 Snow compression and shear strength have a great influence on the tyre traction performance. These parameters cannot be ignored. However, changes of these two aspects can be quantified by vertical and horizontal compaction tests. CTI snow hardness tester can measure and characterize snow surface compaction.

A.1.2 The top of CTI snow hardness tester is a 1.6-mm-radius ball that looks like a plumb (see Figure A.1), and the other end is a measuring rod. Including the knurled nut at the measuring top, the entire instrument, in the laboratory, shall be adjusted to a weight of 220 g ± 1g; the height of the measuring rod shall be adjusted to 218.9 mm ± 0.25 mm.

A.1.3 When using, the ball and the measuring rod are freely dropped at a predetermined height from the rail with the flange end to the tested surface, and the kinetic energy is converted into vertical insertion and horizontal compression. The insertion distance is directly represented by the number (50 ~ 100) from the handheld-scale.

A.1.4 In order to ensure the consistency of the entire test-site, the range of values which is measured from different areas of the test-site shall not exceed 8.

A.2 Instructions for use

A.2.1 When the CTI snow hardness tester is used on site, the instrument shall be placed on the snow surface to ensure that the metal part of the instrument has the same temperature as the snow surface. After each measurement, the head of the measuring rod shall be wiped clean to ensure that no extra snowflakes are inside the instrument. If other factors cause snowflakes inside the instrument, the best way is melting the snowflakes instead of disassembling the instrument. If the instrument needs to be disassembled, be sure to remember clearly the location of all parts before disassembly.

A.2.2 The standard test method is as follows: drive the vehicle with normal tyres on the front wheels over the test-site; then move the vehicle to expose the previous tyre pressing-mark; place the instrument in the center of the tyre pressing-mark; lift up the measuring rod; gently turn the instrument for 45° and […]