GB/T 39971-2021Thresholds and grading of the relative wet grip index for motor vehicle tyres (English PDF)

Foreword

NATIONAL STANDARD OF THE PEOPLE'S REPUBLIC OF CHINA > ICS

Thresholds and grading of relative wet grip index for motor vehicle tyre

Thresholds and grading of relative wet grip index for motor vehicle tyre 1 Scope

This Standard specifies the thresholds and grading requirements and test methods for relative wet grip index for motor vehicle tyre. This Standard is applicable to new car radial tyres and new mini, light truck radial tyres and new truck radial tyres, excluding tyres with nominal rim diameter <=10 inches and nominal rim diameter >=25 inches, T-type spare tyres for temporary use only, special ST metric tyres for road trailers, high-passability radial tyres for light trucks, truck tyres with a speed capability of 80km/h (not included), racing tyres, studded tyres and professional off-road 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 8170, Rules of rounding off for numerical values & expression and judgement of limiting values

GB/T 21910, Method for measuring relative wet grip performance of passenger car tyres

GB/T 35163, Method for measuring relative wet grip performance of truck and bus tyres

3 Terms and definitions

For the purposes of this document, the terms and definitions defined in GB/T 6326 as well as the followings apply.

3.2 professional off-road tyre Tyres that are mainly designed for the use under harsh off-road conditions. For passenger car tyres and mini-light truck tyres with a single tyre load index <= 121 and a speed class of N and above, the groove depth is not less than 11mm, the pattern unsaturation is not less than 35%, and the speed grade is Q and below. For mini, light truck tyres with single tyre load index <=121 and speed class M and below, or mini, light load tyres or truck tyres with single tire load index >121, the groove depth is not less than 16mm, the unsaturation degree of the pattern is not less than 35%, and the speed level is K and below.

3.3 special use tyre Tyres that are mainly designed for the use under special conditions. Compared with ordinary tyres, the block size of this type of tyres is larger, the spacing is wider, and the groove depth is deeper. The tread pattern is a mixture of road and off-road patterns, or off-road patterns. For passenger car tyres and mini-light truck tyres with a single tyre load index <=121 and a speed class of N and above, the depth of the main groove is not less than 11mm, and the unsaturation of the pattern is not less than 35%. For mini, light truck tyres with single tyre load index <=121 and speed class of M and below, or mini, light truck tyres or truck tyres with single tyre load index >121, the depth of the main groove is not less than 16mm, and the unsaturation of the pattern is not less than 35%.