Regulation (EC) No 1222/2009 of the European Parliament and of the CouncilShow full title

[F1 4.2 Testing method using a trailer towed by a vehicle or a tyre test vehicle U.K.

4.2.1 Principle U.K.

The measurements are conducted on test tyres mounted on a trailer towed by a vehicle (hereafter referred to as tow vehicle) or on a tyre test vehicle. The brake in the test position is applied firmly until sufficient braking torque is generated to produce the maximum braking force that will occur prior to wheel lockup at a test speed of 65 km/h.

4.2.2 Equipment U.K.

4.2.2.1 Tow vehicle and trailer or tyre test vehicle U.K.

• The tow vehicle or the tyre test vehicle shall have the capability of maintaining the specified speed of 65 ± 2 km/h even under the maximum braking forces.

• The trailer or the tyre test vehicle shall be equipped with one place where the tyre can be fitted for measurement purposes hereafter called ‘ test position ’ and the following accessories:

  (i)

  equipment to activate brakes in the test position;

  (ii)

  a water tank to store sufficient water to supply the road surface wetting system, unless external watering is used;

  (iii)

  recording equipment to record signals from transducers installed at the test position and to monitor water application rate if the self-watering option is used.

• The maximum variation of toe-settings and camber angle for the test position shall be within ± 0,5 ° with maximum vertical load. Suspension arms and bushings shall have sufficient rigidity necessary to minimise free play and ensure compliance under application of maximum braking forces. The suspension system shall provide adequate load-carrying capacity and be of such a design as to isolate suspension resonance.

• The test position shall be equipped with a typical or special automotive brake system which can apply sufficient braking torque to produce the maximum value of braking test wheel longitudinal force at the conditions specified.

• The brake application system shall be able to control the time interval between initial brake application and peak longitudinal force as specified in section 4.2.7.1.

• The trailer or the tyre test vehicle shall be designed to accommodate the range of candidate tyre sizes to be tested.

• The trailer or the tyre test vehicle shall have provisions for adjustment of vertical load as specified in section 4.2.5.2.

4.2.2.2 Measuring equipment U.K.

• The test wheel position on the trailer or the tyre test vehicle shall be equipped with a rotational wheel velocity measuring system and with transducers to measure the braking force and vertical load at the test wheel.

• General requirements for measurement system: The instrumentation system shall conform to the following overall requirements at ambient temperatures between 0 °C and 45 °C:

  (i)

  overall system accuracy, force: ± 1,5 % of the full scale of the vertical load or braking force;

  (ii)

  overall system accuracy, speed: ± 1,5 % of speed or ± 1,0 km/h, whichever is greater.

• Vehicle speed: To measure vehicle speed, a fifth wheel or non-contact precision speed-measuring system should be used.

• Braking forces: The braking force-measuring transducers shall measure longitudinal force generated at the tyre–road interface as a result of brake application within a range from 0 % to at least 125 % of the applied vertical load. The transducer design and location shall minimise inertial effects and vibration-induced mechanical resonance.

• Vertical load: The vertical load-measuring transducer shall measure the vertical load at the test position during brake application. The transducer shall have the same specifications as described previously.

• Signal conditioning and recording system: All signal conditioning and recording equipment shall provide linear output with necessary gain and data reading resolution to meet the specified previous requirements. In addition, the following requirements apply:

  (i)

  The minimum frequency response shall be flat from 0 Hz to 50 Hz (100 Hz) within ± 1 % full scale.

  (ii)

  The signal-to-noise ratio shall be at least 20/1.

  (iii)

  The gain shall be sufficient to permit full-scale display for full-scale input signal level.

  (iv)

  The input impedance shall be at least 10 times larger than the output impedance of the signal source.

  (v)

  The equipment shall be insensitive to vibrations, acceleration, and changes in ambient temperature.

4.2.3 Conditioning of the test track U.K.

The test track should be conditioned by conducting at least ten test runs with tyres not involved in the test program at 65 ± 2 km/h.

4.2.4 Wetting conditions U.K.

The tow vehicle and trailer or the tyre test vehicle may be optionally equipped with a pavement-wetting system, less the storage tank, which, in the case of the trailer, is mounted on the tow vehicle. The water being applied to the pavement ahead of the test tyres shall be supplied by a nozzle suitably designed to ensure that the water layer encountered by the test tyre has a uniform cross section at the test speed with a minimum splash and overspray.

The nozzle configuration and position shall ensure that the water jets are directed towards the test tyre and pointed towards the pavement at an angle of 20° to 30°.

The water shall strike the pavement 0,25 m to 0,45 m ahead of the centre of tyre contact. The nozzle shall be located 25 mm above the pavement or at the minimum height required to clear obstacles which the tester is expected to encounter, but in no case more than 100 mm above the pavement.

The water layer shall be at least 25 mm wider than the test tyre tread and applied so the tyre is centrally located between the edges. Water delivery rate shall ensure a water depth of 1,0 ± 0,5 mm and shall be consistent throughout the test to within ± 10 per cent. The volume of water per unit of wetted width shall be directly proportional to the test speed. The quantity of water applied at 65 km/h shall be 18 l·s ^-1 per meter of width of wetted surface in case of a water depth of 1,0 mm.

4.2.5 Tyres and rims U.K.

4.2.5.1 Tyre preparation and break-in U.K.

The test tyres shall be trimmed to remove all protuberances on the tread surface caused by mould air vents or flashes at mould junctions.

The test tyre shall be mounted on the test rim declared by the tyre manufacturer.

A proper bead seat should be achieved by the use of a suitable lubricant. Excessive use of lubricant should be avoided to prevent slipping of the tyre on the wheel rim.

The test tyres/rim assemblies shall be stored in a location for a minimum of two hours such that they all have the same ambient temperature prior to testing. They should be shielded from the sun to avoid excessive heating by solar radiation.

For tyre break-in, two braking runs shall be performed under the load, pressure and speed as specified in 4.2.5.2, 4.2.5.3 and 4.2.7.1 respectively.

4.2.5.2 Tyre load U.K.

The test load on the test tyre is 75 ± 5 % of the test tyre load capacity.

4.2.5.3 Tyre inflation pressure U.K.

The test tyre cold inflation pressure shall be 180 kPa for standard-load tyres. For extra-load tyres, the cold inflation pressure shall be 220 kPa.

The tyre pressure should be checked just prior to testing at ambient temperature and adjusted if required.

4.2.6 Preparation of the tow vehicle and trailer or the tyre test vehicle U.K.

4.2.6.1 Trailer U.K.

For one axle trailers, the hitch height and transverse position shall be adjusted once the test tyre has been loaded to the specified test load in order to avoid any disturbance of the measuring results. The longitudinal distance from the centre line of the articulation point of the coupling to the transverse centre line of the axle of the trailer shall be at least 10 times the ‘ hitch height ’ or the ‘ coupling (hitch) height ’ .

4.2.6.2 Instrumentation and equipment U.K.

Install the fifth wheel, when used, in accordance with the manufacturer’s specifications and locate it as near as possible to the mid-track position of the tow trailer or the tyre test vehicle.

4.2.7 Procedure U.K.

4.2.7.1 Test run U.K.

The following procedure applies for each test run:

(1)

The tow vehicle or the tyre test vehicle is driven onto the test track in a straight line at the specified test speed 65 ± 2 km/h.

(2)

The recording system is launched.

(3)

Water is delivered to the pavement ahead of the test tyre approximately 0,5 s prior to brake application (for internal watering system).

(4)

The trailer brakes are activated within 2 metres of a measurement point of the wetted frictional properties of the surface and sand depth in accordance with points 4 and 5 of section 3.1. The rate of braking application shall be such that the time interval between initial application of force and peak longitudinal force is in the range 0,2 s to 0,5 s.

(5)

The recording system is stopped.

4.2.7.2 Test cycle U.K.

A number of test runs are made in order to measure the wet grip index of the candidate tyre (T) according to the following procedure, whereby each test run shall be made at the same spot on the test track and in the same direction. Up to three candidate tyres may be measured within the same test cycle, provided that the tests are completed within one day.

(1)

First, the reference tyre is tested.

(2)

After at least six valid measurements are performed in accordance with section 4.2.7.1, the reference tyre is replaced by the candidate tyre.

(3)

After six valid measurements of the candidate tyre are performed, two more candidate tyres may be measured.

(4)

The test cycle is closed by six more valid measurements of the same reference tyre as at the beginning of the test cycle.

EXAMPLES: U.K.

• The run order for a test cycle of three candidate tyres (T1 to T3) plus the reference tyre (R) would be the following:

  R-T1-T2-T3-R

• The run order for a test cycle of five candidate tyres (T1 to T5) plus the reference tyre R would be the following:

  R-T1-T2-T3-R-T4-T5-R

4.2.8 Processing of measurement results U.K.

4.2.8.1 Calculation of the peak braking force coefficient U.K.

The tyre peak braking force coefficient ( μ _peak ) is the highest value of μ(t) before lockup occurs calculated as follows for each test run. Analogue signals should be filtered to remove noise. Digitally recorded signals must be filtered using a moving average technique.

where:

• μ(t) is the dynamic tyre braking force coefficient in real time;

• fh(t) is the dynamic braking force in real time, in N;

• fv(t) is the dynamic vertical load in real time, in N.

4.2.8.2 Validation of results U.K.

The μ _peak coefficient of variation is calculated as follows:

(Standard Deviation / Average) x 100

For the reference tyre (R)

:

If the coefficient of variation of the peak braking force coefficient ( μ _peak ) of the reference tyre is higher than 5 %, all data should be discarded and the test repeated for all test tyres (the candidate tyre(s) and the reference tyre).

For the candidate tyre(s) (T)

:

The coefficient of variation of the peak braking force coefficient ( μ _peak ) is calculated for each candidate tyre. If one coefficient of variation is higher than 5 %, the data should be discarded and the test repeated for this candidate tyre.

4.2.8.3 Calculation of the adjusted average peak braking force coefficient U.K.

The average peak braking force coefficient of the reference tyre used for the calculation of its braking force coefficient is adjusted according to the positioning of each candidate tyre in a given test cycle.

This adjusted average peak braking force coefficient of the reference tyre ( Ra ) is calculated in accordance with table 3 where R ₁ is the average peak tyre braking coefficient in the first test of the reference tyre (R) and R ₂ is the average peak tyre braking coefficient in the second test of the same reference tyre (R).

Table 3

Number of candidate tyre(s) within one test cycle	Candidate tyre	Ra
1 ( R 1 -T1- R 2 )	T1	Ra = 1/2 ( R 1 + R 2 )
2 ( R 1 -T1-T2- R 2 )	T1	Ra = 2/3 R 1 + 1/3 R 2
	T2	Ra = 1/3 R 1 + 2/3 R 2
3 ( R 1 -T1-T2-T3- R 2 )	T1	Ra = 3/4 R 1 + 1/4 R 2
	T2	Ra = 1/2 ( R 1 + R 2 )
	T3	Ra = 1/4 R 1 + 3/4 R 2

4.2.8.4 Calculation of the average peak braking force coefficient ( μ _peak,ave ) U.K.

The average value of the peak braking force coefficients ( μ _peak,ave ) is calculated according to table 4 whereby Ta ( a = 1, 2 or 3) is the average of the peak braking force coefficients measured for one candidate tyre within one test cycle.

Table 4

Test tyre	μ peak,ave
Reference tyre	μ peak,ave (R) = Ra as per Table 3
Candidate tyre	μ peak,ave (T) = Ta

4.2.8.5 Calculation of the wet grip index of the candidate tyre U.K.

The wet grip index of the candidate tyre ( G(T) ) is calculated as follows:

where:

• t is the measured wet surface temperature in degree Celsius when the candidate tyre ( T ) is tested

• t ₀ is the wet surface reference temperature condition

• t ₀ = 20 °C for normal tyres t ₀ = 10 °C for snow tyres

• μ _peak,ave (R ₀ ) = 0,85 is the peak braking force coefficient for the reference tyre in the reference conditions

• a = – 0,4232 and b = - 8,297 for normal tyres, a = 0,7721 and b = 31,18 for snow tyres.]

Textual Amendments

F1 Inserted by Commission Regulation (EU) No 228/2011 of 7 March 2011 amending Regulation (EC) No 1222/2009 of the European Parliament and of the Council with regard to the wet grip testing method for C1 tyres (Text with EEA relevance).