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This standard is developed in accordance with the rules given in GB/T 1.1-2009.
This standard has been redrafted and modified in relation to ISO 15222: 2011 Method for measuring relative wet grip performance of truck and bus tyres.
Annex A gives a comparison between this standard and ISO 15222:2011 in clause number.
The technical deviations have been made in this standard with respect to ISO 15222: 2011, 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 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).
Method for measuring relative wet grip performance of truck and bus tyres
1 Scope
This standard specifies the method for measuring relative wet grip braking performance for truck & bus tyres.
The test method of comparison with standard reference test tyre is adopted in this standard.
This standard applies to new truck & bus 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 9744 Truck tyres
ASTM E303 Standard test method measuring surface frictional properties using the British pendulum tester
ASTM E965 Standard test method for measuring pavement macrotexture depth using a volumetric technique
3 Terms and definitions
For the purposes of this document, the terms and definitions given in GB/T 6326 and the following apply.
3.1
candidate tyre
tyre that is evaluated by testing
3.2
standard reference test tyre; SRTT
a set of special candidate tyres that are used as a benchmark in an evaluation system These tyres usually have carefully controlled design features to minimize variation and they are produced, controlled and stored according to the relevant standards
3.3
control tyre
tyre which is used to indirectly obtain the comparison result between candidate tyre and standard reference test tyre by comparing with the candidate tyre and then the standard reference test tyre when the candidate tyre and the standard reference test tyre cannot be compared on the same vehicle
3.4
braking force of a tyre
longitudinal force, expressed in newtons, 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 lockup of wheel as the braking torque is progressively increased
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
3.10
coupling (hitch) height
height measured perpendicularly from the center of the articulation point of the towing vehicle or hitch to the ground, when the towing vehicle and trailer are coupled together
Note: during testing, the towing vehicle and trailer shall be standing on level road surface and equipped with the appropriate tyre(s) to be used in different tests.
4 Classification of test methods
Wet grip braking performance for 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 using a trailer or a tyre test vehicle equipped with tyres.
5 Test conditions
5.1 Road surface conditions
5.1.1 The test road surface shall have a uniform grade of not more than 2% and shall not deviate more than 6mm when tested with a 3m straight edge.
5.1.2 The surface shall have a pavement of uniform composition, age and wear. The surface shall be free of loose material and foreign deposits.
5.1.3 The surface shall be a dense asphalt surface. The maximum nominal particle size shall be from 8mm to 13mm.
5.1.4 The sand depth measured as specified in ASTM E965, shall be 0.7mm±0.3mm.
5.1.5 In order to verify the wetted frictional properties of the test road surface, one of the following methods shall be used:
a) British Pendulum Number (BPN) method
The average BPN using the pendulum tester shall be between 42~60 after temperature correction based on Equations (1) and (2). Measurements for BPN shall be taken every 10m on the test road surface, and the operation shall be repeated five times at each point of the BPN measurement; the coefficient of variation of the average BPN shall not exceed 10%.
Temperature correction = (-0.0018t2)+0.34t-6.1 (1)
BPN = BPN (measurement) + temperature correction (2)
Where,
t——the road surface temperature, ℃.
To decrease the dispersion of test results, the BPN values of the test road surface shall not vary over the entire braking distance.
Composition and physical characteristics of friction blockcompound composition 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 3.2mm in the plane of the slider or 1.6mm vertical to it in accordance with ASTM E303.
b) SRTT method
For the trailer method, the average peak braking force coefficient shall be 0.7±0.1 at 65km/h after temperature correction using Equations (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)
Average peak braking coefficient (μpeak ave) = peak braking coefficient (measurement)+temperature correction (4)
Where,
t——the wetted road surface temperature, ℃.
5.2 Wetting conditions
5.2.1 The test road surface may be wetted by a wetting system on road side or incorporated into the tyre test vehicle (trailer). If side watering is used, water the test road surface at least half an hour prior to testing in order to equalize the test road 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 road surface shall be between 0.5mm~2 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 by more than 10℃ during the test.
5.4 Standard reference test tyre
Three SRTT sizes shall be used for the testing of truck & bus tyres, including 315/70R 22.5 154/150L, 245/70R 19.5136/134M and 225/75R 16LT 116/114S, which shall conform to the requirements of relevant group standards of China, as detailed in Table 1.
Table 1
Candidate tyre Standard reference test tyre
Tiny and light truck and bus tyres Single tyre load index ≤121 (single tyre load capacity ≤1450kg) and speed level of N or above 225/75R16 LT 116/114 S
Single tyre load index ≤121 (single tyre load capacity ≤1450kg), and the speed level of M or below, or single tyre load index >121 (single tyre load capacity >1450kg) SN<285 mm 245/70R19.5 136/134 M
SN≥285 mm 315/70R22.5 154/150 L
Truck & bus tyres SN<285 mm 245/70R19.5 136/134 M
SN≥285 mm 315/70R22.5 154/150 L
Note: SN——nominal section width of a tyre.
6 Vehicle 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 60km/h and a final speed of 20km/h.
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Classification of test methods
5 Test conditions
6 Vehicle method
7 Test method using a trailer or a tyre test vehicle
8 Test report
Annex A (Informative) Comparison table between the clause numbers in this standard and those in ISO 15222:
Annex B (Informative) Technical differences between this standard and ISO 15222: 2011 and their reasons
Annex C (Informative) Example test report of wet grip index
