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This standard is developed in accordance with the rules given in GB/T 1.1-2009.
It replaces GB/T 21910-2008 Method for measuring relative wet grip performance of passenger car tyres. The following technical changes have been made with respect to GB/T 21910-2008:
——the test conditions were revised, including road surface, water film and weather conditions (see Clause 5);
——the requirement on braking force application by brake pedal is delete (see Subclause 6.1 in Edition 2008);
——the calculation formula is standardized, and the standard reference temperature conditions for wet road surface of snow tyres and the braking force coefficient of SRTTs under standard conditions are added (see Subclauses 6.7.5, 6.8.2 and 7.7.6);
——the requirements on watering volume and depth in the trailer method are added (See subclause 7.2.2);
——the requirements on transducers in braking force measuring devices are deleted (see subclause 7.2.3.3, Edition 2008);
——the requirement on input impedance in "signal processing and recording device" is modified. The requirements on digital signal sampling frequency and relative error are deleted. The requirements for frequency, acceleration and signal distortion of test equipment is deleted (see Subclause 7.2.3.5 in this edition; Subclause 7.2.3.5, Edition 2008);
——the requirements on candidate tyre are modified (see Subclauses 7.3.2 and 7.3.5 in this edition; Subclauses 7.3.2 and 7.3.5 in Edition 2008);
——the run number of conditioning is modified (see Subclause 7.3.3 in this edition; Subclause 7.3.3 in Edition 2008);
——the time requirement for placing the tyre rim assembly in the test site is added (see Subclause 7.3.4).
This standard has been redrafted and modified in relation to ISO 23671: 2015 Passenger car tyres - Method for measuring relative wet grip performance - Loaded new tyres.
Annex A gives a comparison between clause numbers in this standard and those in ISO 23671:2015.
The technical deviations have been made in this standard with respect to ISO 23671: 2015, and marked with a perpendicular single line (|) at the page margin of relevant clauses.
For the convenience of application, the following editorial modifications are made in this standard:
——the standard name is modified;
——the bibliography is deleted.
This standard was proposed by the China Petroleum and Chemical Industry Association.
This standard is under the jurisdiction of the National Technical Committee on Tyres and Rims of Standardization Administration of China (SAC/TC 19).
The previous edition replaced by this standard is as follows:
—— GB/T 21910-2008.
Method for measuring relative wet grip performance of passenger car tyres
1 Scope
This standard specifies the method for measuring wet grip performance of tyres for use on passenger cars braking on a wet-paved surface, and it is used to assess the wet grip capability of tyres for use on passenger cars braking on a wet-paved surface.
The test method of comparison with standard reference test tyre is adopted in this standard.
This standard is applicable to new passenger car tyres.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 6326 Tyre terms and definitions (GB/T 6326-2014, ISO 4223-1:2002, NEQ)
GB 9743 Passenger car tyres
ASTM E303-93 (Reapproved 2013) Standard test method measuring surface frictional properties using the British pendulum tester
ASTM E965-96 (Reapproved 2006) Standard test method for measuring pavement macrotexture depth using a volumetric technique
3 Terms and definitions
For the purpose of this standard, the terms and definitions established in GB/T 6326 as well as the following ones apply.
3.1
candidate tyre
tyre that is evaluated by testing
3.2
standard reference test tyre; SRTT; reference tyre
special test tyre (set) that is used as a benchmark in an evaluation programme. These tyres usually have carefully controlled design features to minimize variation. They are produced, controlled and stored according to relevant
?
3.3
control tyre
tyre (set) that is used to indirectly work out the comparison result between SRTT amd candidate tyre by comparing it with candidate tyre and then with SRTT when the candidate tyre and the reference tyre cannot be directly compared on the same vehicle
3.4
braking force of a tyre
longitudinal force, expressed in newtons (N), resulting from braking torque application
3.5
braking force coefficient of a tyre; BFC
ratio of braking force to vertical load
3.6
peak braking force coefficient of a tyre
maximum value of tyre braking force coefficient that occurs prior to wheel lockup as the braking is applied
3.7
lockup of a wheel
condition of a wheel in which its rotational velocity about the wheel spin axis is zero and it is prevented from rotating in the presence of applied wheel torque
3.8
vertical load
normal reaction of the tyre on the road
3.9
tyre test vehicle
dedicated vehicle which has instruments to measure the vertical and the longitudinal forces on one tyre during braking
4 Methods for measuring wet grip
Grip braking performance for passenger car tyres on a wet paved surface can be measured by one of the following methods:
—— vehicle method, consisting of testing a set of tyres mounted on a test vehicle;
—— (trailer method) test method using a trailer or a tyre test vehicle equipped with the test tyres.
5 Test condition
5.1 Track characteristics
5.1.1 The track surface shall have a uniform grade of not more than 2% and shall not deviate more than 6 mm at length or width direction when tested with a 3 m straight edge.
5.1.2 The test surface shall have a pavement of uniform age, composition, and wear. The test surface shall be free of loose material and foreign deposits.
5.1.3 The test surface shall be a dense asphalt surface. The maximum nominal chipping size shall be from 8 mm to 13 mm.
5.1.4 The texture depth on the test surface measured as specified in ASTM E965-96 shall be (0.7 ± 0.3) mm.
5.1.5 In order to verify the frictional properties of the surface, a) or b) shall be used:
a) British Pendulum Number (BPN) method
The averaged British Pendulum Number (BPN) shall be between 42 and 60 after temperature correction using Formulas (1) and (2). BPN shall be tested on a point per 10 m, 5 times on each point, according to the requirements of ASTM E303-93. The coefficient of variation for the averaged BPN is not larger than 10%.
Temperature correction = (-0.0018 t2) + 0.34t - 6.1 (1)
BPN = BPN (measured value) + temperature correction (2)
Where,
t——the road surface temperature, ℃.
To decrease the dispersion of test results, the BPN values of the test surface shall not vary over the entire stopping distance.
Composition and physical characteristics of friction block characteristics of compounds for pendulum tester shall conform to relevant requirements.
The pad shall be removed for maximum wear when the wear on the striking edge of the slider reaches 3.2 mm in the plane of the slider or 1.6 mm vertical to it in accordance with ASTM E303-93.
b) Standard Reference Test Tyre (SRTT) method
For the trailer method, the average peak braking force coefficient shall be 0.7 ± 0.1 at 65 km/h after temperature correction using Formulas (3) and (4). Testing is run on a road surface with a length of less than 10m, and the braking position deviation on the test road surface is within 2m.
Temperature correction = 0.0035 (t-20) (3)
peak braking force coefficient (μpeak,ave) = peak braking force coefficient (measured) + temperature correction (4)
Where,
t——the wetted road surface temperature, ℃.
5.2 Wetting conditions
5.2.1 The test surface may be wetted by a wetting system on road side or incorporated into the tyre test vehicle or the trailer. If side watering is used, water the test surface at least half an hour (0.5 h) prior to testing in order to equalize the test surface temperature and water temperature.
5.2.2 Watering shall be supplied continuously throughout testing, the water depth measured from the middle position of the test surface shall be between 1.0 mm ~ 0.5 mm, and shall be uniform throughout testing.
5.3 Atmospheric conditions
5.3.1 The wind conditions shall not interfere with wetting of the surface (wind-shields are allowed where necessary).
5.3.2 The ambient and the wetted surface temperatures shall be between 2℃~20℃ for testing snow tyres while 5℃~35℃ for testing normal tyres, and shall not vary during the test by more than 10℃. The ambient temperature shall remain close to the wetted surface temperature; the difference between the ambient and the wetted surface temperature shall be less than 10℃.
5.4 Standard reference test tyre (SRTT)
The specification of standard reference test tyre is 225/60R16 97S and shall meet the requirements of corresponding group standards in China.
6 SRTT method
6.1 Principle
The test method covers a procedure for measuring the deceleration performance of tyres during braking, using a test vehicle having an Antilock Braking System (ABS). Starting with a defined initial speed, the brakes are applied hard enough on the four tyres at the same time to activate the ABS. The average deceleration (AD) is calculated between two defined speeds, with an initial speed of 80 km/h and a final speed of 20km/h.
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Methods for measuring wet grip
5 Test condition
5.1 Track characteristics
5.2 Wetting conditions
5.3 Atmospheric conditions
5.4 Standard reference test tyre (SRTT)
6 SRTT method
6.1 Principle
6.2 Equipment
6.3 Conditioning of the test road
6.4 Test speed measurement requirements
6.5 Tyres and rims
6.6 Procedure
6.7 Processing of measurement results
6.8 Wet grip performance comparison between a candidate tyre and a SRTT using a control tyre
7 Test method using a trailer or a tyre test vehicle
7.1 Principle
7.2 Test apparatus
7.3 Selection and preparation of test tyres
7.4 Preparation of apparatus and test track
7.5 Test load
7.6 Test procedure
7.7 Processing of test data
8 Test report
Annex A (Informative) Comparison between clause numbers in this standard and those in ISO 23671:
Annex B (Informative) Technical differences between this standard and ISO 23671: 2015 and their reasons
Annex C (Informative) Example test report of wet grip index
