(6.)

6.1. Dimensional requirements 6.1.1. Section width of a tyre 6.1.1.1. Except as provided by section 6.1.1.2, the section width is calculated by the following formula: S = S1, + K (A-A1) where: S = the section width expressed in mm ( 12 ) and measured on the measuring rim; S1 = the nominal section width in mm as shown on the sidewall of the tyre in the tyre-size designation as prescribed; A = the width (expressed in mm) of the measuring rim, as shown by the manufacturer in the descriptive note, (see section 6.11 of Annex I, Appendix 1); A1 = the width (expressed in mm) of the theoretical rim; it is taken to equal S1 multiplied by the factor x as specified by the tyre manufacturer (see section 6.15 of Annex I, Appendix 1); and K is taken to equal 0.4. 6.1.1.2. However, for the types of tyre for which the size designation is given in the first column of the tables in Appendix 5 A or 5 B, the measuring rim width (A) and the section width (S) are those given opposite the tyre size designation in those tables. 6.1.2. Outer diameter of a tyre 6.1.2.1. Except as provided by secton 6.1.2.2, the outer diameter of a tyre is calculated by the following formula: D = d + 0,02H where: D = is the outer diameter expressed in mm, d = is the conventional number defined in section 2.17.1.3, expressed in mm, H = is the nominal section heigth in mm and is equal to S1 × 0,01 Ra; where: Ra = is the nominal aspect ratio, all as shown on the sidewall of the tyre in the tyre-size designation in conformity with the requirements of section 3. 6.1.2.2. However, for the types of tyres for which the size designation is given in the first column of the tables of Appendix 5 the outer diameter is that given opposite the tyre size designation in those tables. 6.1.3. Method of measuring tyre dimensions The actual dimensions of tyres are measured as prescribed in Appendix 6. 6.1.4. Tyre section width: specification of tolerance 6.1.4.1. The overall width of a tyre may be less than the section width determined pursuant to section 6.1.1 or shown in Appendix 5; 6.1.4.2. It may not exceed that value by more than the following: 6.1.4.2.1. diagonal (bias-ply) tyres: 6 % for passenger car tyres, 8 % for commercial vehicle tyres; 6.1.4.2.2. radial-ply tyres: 4 %; and 6.1.4.2.3. in addition, if the tyre has a special protective band, the figure as increased by the above tolerances may be exceeded by 8 mm. 6.1.4.2.4. However, for tyres of a section width exceeding 305 mm intended for dual (twin) mounting the nominal value must not be exceeded by more than 2 % for radial-ply or 4 % for diagonal (bias-ply) tyres. 6.1.5. Tyre outer diameter: specification of tolerance The outer diameter of a tyre must not be outside the values Dmin and Dmax obtained from the following formulae: Dmin = d + (2H × a) Dmax = d + (2H × b) 6.1.5.1. for sizes listed in Appendix 5: H = 0,5 (D — d) — (for references see section 6.1.2.2). 6.1.5.2. for other sizes not listed in Appendix 5: H and d are as defined in section 6.1.2.1. 6.1.5.3. coefficients a and b are respectively: 6.1.5.3.1. coefficient a = 0,97; 6.1.5.3.2. coefficient b for normal, special, snow or temporary-use spare tyres



Category of use Passenger car tyres Commercial vehicle tyres Radial Bias Radial Bias Normal 1,04 1,08 1,04 1,07 Special — — 1,06 1,09 Snow 1,04 1,08 1,04 1,07 Temporary-use 1,04 1,08 — — 6.1.5.4. For snow tyres the outer diameter (Dmax) established in conformity with the above may be exceeded by 1 %. 6.2. Load/speed test requirement 6.2.1. The tyre must undergo a load/speed test carried out in accordance with the relevant procedure described in Appendix 7. 6.2.2. A tyre which, after undergoing the relevant load/speed test, does not exhibit any tread separation, ply separation, cord separation, chunking or broken cords is deemed to have passed the test. 6.2.3. The outer diameter of the tyre, measured six hours after the load/speed test, must not be more than 3,5 % greater than the outer diameter as measured before the test. 6.2.4. Where application is made for the approval of a type of commercial vehicle tyre the load/speed combinations given in the table in Appendix 8 apply and, the load/speed test prescribed in section 6.2.1 need not be carried out for load and speed values other than the nominal values. 6.2.5. Where application (see secton 6.13 of Annex 1, Appendix 1) is made for the approval of a type of commercial vehicle tyre which has a load/speed combination in addition to the one that is subject to the variation of load with speed given in the table in Appendix 8, the load/speed test prescribed in section 6.2.1 must also be carried out on a second tyre of the same type at the additional load/speed combination. 6.2.6. Where a tyre manufacturer produces a range of tyres it is not considered necessary to carry out a load/speed test on every type of tyre in the range. Worst-case selection may be made, at the discretion of the approval authority. 6.3. Tread-wear indicators 6.3.1. In the case of passenger car tyres the tread of the tyre must include not less than six transverse rows of tread-wear indicators, approximately equally spaced and situated in the wide grooves in the central zone of the tread, which covers approximately three quarters of the tread width. The tread-wear indicators must be such that they cannot be confused with the rubber ridges between the ribs or blocks of the tread. 6.3.2. However, in the case of tyres of dimensions appropriate for mounting on rims of a nominal diamter of 12″ or less, four rows of tread-wear indicators are acceptable. 6.3.3. The tread-wear indicators must give visual warning when the depth of the corresponding tread grooves has been reduced to 1,6 mm with a tolerance of + 0,6/- 0 mm.