ANNEX VI

Laboratory alignment procedure for the measurement of rolling resistance

1. Definitions

For the purposes of the laboratory alignment procedure, the following definitions shall apply:

1. ‘reference laboratory’ means a laboratory that is part of the network of laboratories the name of which have been published for the purpose of the alignment procedure in the Official Journal of the European Union, and is able to achieve the accuracy of test results determined in Section 3 with its reference machine;

2. ‘candidate laboratory’ means a laboratory participating in the alignment procedure that is not a reference laboratory;

3. ‘alignment tyre’ means a tyre that is tested for the purpose of performing the alignment procedure;

4. ‘alignment tyres set’ means a set of five or more alignment tyres for the alignment of one single machine;

5. ‘assigned value’ means a theoretical value of the Rolling Resistance Coefficient (RRC) of one alignment tyre as measured by a theoretical laboratory which is representative of the network of reference laboratories that is used for the alignment procedure;

6. ‘machine’ means every tyre testing spindle in one specific measurement method. For example, two spindles acting on the same drum shall not be considered as one machine.

2. General provisions

2.1. Principle

The measured (m) Rolling Resistance Coefficient in a reference laboratory (l), (RRCm, l ), shall be aligned to the assigned values of the network of reference laboratories.

The measured (m) Rolling Resistance Coefficient obtained by a machine in a candidate laboratory (c), RRCm, c , shall be aligned through one reference laboratory of the network of its choice.

2.2. Tyre selection requirements

A set of five or more alignment tyres shall be selected for the alignment procedure in compliance with the criteria below. One set shall be selected for C1 and C2 tyres together, and one set for C3 tyres.

(a) The set of alignment tyres shall be selected so as to cover the range of different RRCs of C1 and C2 tyres together, or of C3 tyres. In any event, the difference between the highest RRCm of the tyre set, and the lowest RRCm of the tyre set shall be, before and after alignment, at least equal to: (i) 3 kg/t for C1 and C2 tyres; and (ii) 2 kg/t for C3 tyres.

(b) The RRCm in the candidate or reference laboratories (RRCm, c or RRCm, l ) based on declared RRC values of each alignment tyre of the set shall be distributed evenly.

(c) Load index values shall adequately cover the range of the tyres to be tested, ensuring that the rolling resistance force values also cover the range of the tyres to be tested.

Each alignment tyre shall be checked prior to use and replaced when:

(a) it shows a condition which makes it unusable for further tests; and/or

(b) there are deviations of RRCm, c or RRCm, l greater than 1,5 per cent relative to earlier measurements after correction for any machine drift.

2.3. Measurement method

The reference laboratory shall measure each alignment tyre four times and retain the three last results for further analysis, in accordance with paragraph 4 of Annex 6 of UNECE Regulation No 117 and its subsequent amendments and applying the conditions set out in paragraph 3 of Annex 6 of UNECE Regulation No 117 and its subsequent amendments.

The candidate laboratory shall measure each alignment tyre (n + 1) times with n being specified in Section 5 and retain the n last results for further analysis, in accordance with paragraph 4 of Annex 6 of UNECE Regulation No 117 and its subsequent amendments and applying the conditions set out in paragraph 3 of Annex 6 of UNECE Regulation No 117 and its subsequent amendments.

Each time an alignment tyre is measured, the tyre/wheel assembly shall be removed from the machine and the entire test procedure specified in paragraph 4 of Annex 6 of UNECE Regulation No 117 and its subsequent amendments shall be followed again from the start.

The candidate or reference laboratory shall calculate:

(a) the measured value of each alignment tyre for each measurement as specified in Annex 6, paragraphs 6.2 and 6.3, of UNECE Regulation No 117 and its subsequent amendments (i.e. corrected for a temperature of 25 oC and a drum diameter of 2 m);

(b) the mean value of the three (in the case of reference laboratories) or n (in the case of candidate laboratories) last measured values of each alignment tyre; and

(c) the standard deviation (σm) as follows: where: i is the counter from 1 to p for the alignment tyres; j is the counter from 2 to n+1 for the n last repetitions of each measurement of a given alignment tyre n+1 is the number of repetitions of tyre measurements (n+1=4 for reference laboratories and n+1 ≥4 for candidate laboratories); p is the number of alignment tyres (p ≥ 5).

2.4. Data formats to be used for the computations and results

— The measured RRC values corrected from drum diameter and temperature shall be rounded to 2 decimal places.

— Then the computations shall be made with all digits: there shall be no further rounding except on the final alignment equations.

— All standard deviation values shall be displayed to 3 decimal places.

— All RRC values will be displayed to 2 decimal places.

— All alignment coefficients (A1l, B1l, A2c and B2c) shall be rounded and displayed to 4 decimal places.

3. Requirements applicable to the reference laboratories and determination of the assigned values

The assigned values of each alignment tyre shall be determined by a network of reference laboratories. Every second year the network shall assess the stability and validity of the assigned values.

Each reference laboratory participating in the network shall comply with the specifications of Annex 6 of UNECE Regulation No 117 and its subsequent amendments and have a standard deviation (σm) as follows:

(a) not greater than 0,05 kg/t for class C1 and C2 tyres; and

(b) not greater than 0,05 kg/t for class C3 tyres.

The sets of alignment tyres, conforming to the specification of Section 2.2 shall be measured in accordance with Section 2.3 by each reference laboratory of the network.

The assigned value of each alignment tyre is the average of the measured values given by the reference laboratories of the network for this alignment tyre.

4. Procedure for the alignment of a reference laboratory to the assigned values

Each reference laboratory (l) shall align itself to each new set of assigned values and always after any significant machine change or any drift in machine control tyre monitoring data.

The alignment shall use a linear regression technique on all individual data. The regression coefficients, A1l and B1l, shall be calculated as follows:

where:

RRC is the assigned value of the rolling resistance coefficient;

RRCm, l is the individual measured value of the rolling resistance coefficient by the reference laboratory ‘l’ (including temperature and drum diameter corrections).

5. Requirements applicable to candidate laboratories

Candidate laboratories shall repeat the alignment procedure at least once every second year for every machine and always after any significant machine change or any drift in machine control tyre monitoring data.

A common set of five different tyres, conforming to the specification of Section 2.2 shall be measured in accordance with Section 2.3 firstly by the candidate laboratory and later on by one reference laboratory. More than five alignment tyres may be tested at the request of the candidate laboratory.

The alignment tyre set shall be provided by the candidate laboratory to the selected reference laboratory.

The candidate laboratory (c) shall comply with the specifications of Annex 6 of UNECE Regulation No 117 and its subsequent amendments and preferably have standard deviations (am) as follows:

(a) not greater than 0,075 kg/t for C1 and C2 tyres; and

(b) not greater than 0,06 kg/t for C3 tyres.

If the standard deviation (σm) of the candidate laboratory is higher than the above values with four measurements, the last three ones being used for the computations, then the number n+1 of measurement repetitions shall be increased as follows for the entire batch:

n+1 = 1+(σm/γ)2 , rounded up to the nearest higher integer value

where:

γ = 0,043 kg/t for Class C1 and C2 tyres

γ = 0,035 kg/t for Class C3 tyres

6. Procedure for the alignment of a candidate laboratory

One reference laboratory (i) of the network shall calculate the linear regression function on all individual data of the candidate laboratory (c). The regression coefficients, A2c and B2c, shall be calculated as follows:

where:

RRCm, l is the individual measured value of the rolling resistance coefficient by the reference laboratory (i) (including temperature and drum diameter corrections)

RRCm, c is the individual measured value of the rolling resistance coefficient by the candidate laboratory (c) (including temperature and drum diameter corrections)

If the coefficient of determination R2 is lower than 0,97, the candidate laboratory shall not be aligned.

The aligned RRC of tyres tested by the candidate laboratory is calculated as follows: