EN    EN EN EN    EN  EUROPEAN COMMISSION 
Brussels, XXX 
C(2010) YYY final 
Draft 
COMMISSION REGULATION (EU) No …/.. 
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 EN 2   EN Draft 
COMMISSION REGULATION (EU) No …/.. 
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 
THE EUROPEAN COMMISSION, 
Having regard to the Treaty on the Functioning of the European Union,  Having regard to Regulation (EC) No 1222/2009 of the European Parliament and of the 
Council of 25 November 2009 on the labelling of ty res with respect to fuel efficiency and 
other essential parameters
1, and in particular Article 11 (c) thereof, 
Whereas: (1) In accordance with Annex I, part B of  Regulation (EC) No 1222/2009, the wet grip 
index of C1 tyres shall be determined as  specified in UNECE Regulation No 117 and 
its subsequent amendments. However, repres entatives of the indus try have developed 
a revised wet grip testing method on the ba sis of Annex 5 of UNECE Regulation No 
117 that significantly improves the accuracy of the testing results. 
(2) Accuracy of testing results is a key factor for determining wet grip classes of tyres. It 
ensures a fair comparison between tyres from  different suppliers. In addition, accurate 
testing prevents that a tyre may be classifi ed into more than one class and reduces the 
risks that different testing results will be obtained by market surveillance authorities in 
comparison to the testing results declared  by the suppliers on ly because of the 
uncertainty of the testing method. 
(3) Therefore, it is necessary to update we t grip testing method in order to improve 
accuracy of the tyre testing results. 
(4) Regulation (EC) No 1222/2009 should therefore be amended accordingly. 
(5) The measures provided for in this Regulat ion are in accordance with the opinion of the 
Committee established by Article 13  of Regulation (EC) No 1222/2009, 
HAS ADOPTED THIS REGULATION: 
Article 1 
Amendment to Regulation (EC) No 1222/2009 
Regulation (EC) No 1222/2009 is amended as follows: 
                                                
 
1 OJ L 342, 22.12.2009, p. 46 .  EN 3   EN (1) In Annex I, part B, the first se ntence is replaced by the following:  
"The wet grip class of C1 tyres must be dete rmined on the basis of the wet grip index (G) 
according to the "A" to "G" scale specified in  the table below and measured in accordance 
with Annex V."; 
(2) The text set out in the annex to this Regulation is added as Annex V. 
Article 2 
Entry into force 
This Regulation shall enter into force on the twentieth day following that of its publication in 
the Official Journal of  the European Union . 
This Regulation shall be binding in its entirety a nd directly applicable in the Member States in 
accordance with the Treaties. 
Done at Brussels, […] 
 For the Commission 
 The President 
 […] 
 EN 4   EN ANNEX  
"ANNEX V 
Testing method for measuring the wet grip index (G) of C1 tyres 
1. M ANDATORY STANDARDS  
The following documents listed apply.  
(1) ASTM E 303-93 (Reapproved 2003), Standa rd Test Method for Measuring Surface 
Frictional Properties Using th e British Pendulum Tester; 
(2) ASTM E 501-06, Standard Specification for Standard Rib Tire for Pavement Skid-
Resistance Tests; 
(3) ASTM E 965-96 (Reapproved 2001), Standard  Test Method for Measuring Pavement 
Macrotexture Depth Using a Volumetric Technique; 
(4) ASTM E 1136-93 (Reapproved 2008), Standard Specification for a Radial Standard 
Reference Test Tire (SRTT14”); 
(5) ASTM F 2493-08, Standard Specification for a Radial Standard Re ference Test Tire 
(SRTT16”). 
2. DEFINITIONS 
For the purposes of testing wet grip of C1 tyres, the following definitions apply: 
(1) 'test run' means a single pass of a load ed tyre over a given test track surface; 
(2) 'test tyre(s)' means a candidate tyre, a refere nce tyre or a control tyre or tyre set that 
is used in a test run; 
(3) 'candidate tyre(s) (T)' means a tyre or a tyre set th at is tested for the purpose of 
calculating its wet grip index;  
(4) 'reference tyre(s) (R)' means a tyre or a tyre set that  has the characteristics indicated 
in ASTM F 2493-08 and referred to as St andard Reference Test Tyre 16 inches 
(SRTT16”); 
(5) 'control tyre(s) (C)' means an intermediate tyre or a set of intermediate tyres which is 
used when the candidate tyre and the refere nce tyre cannot be directly compared on 
the same vehicle; 
(6) 'braking force of a tyre' means the longit udinal force, expresse d in newton, resulting 
from braking torque application; 
(7) 'braking force coefficient of a tyre (BFC) ' means the ratio of the braking force to the 
vertical load; EN 5   EN (8) 'peak braking force coefficient of a tyre' means the maximum value of a tyre braking 
force coefficient that occurs prior to wheel lockup as the braking torque is 
progressively increased; 
(9) 'lockup of a wheel' means the 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; 
(10) 'vertical load' means the load in ne wton or kilogram force imposed on the tyre 
perpendicular to the road surface; 
(11) 'tyre test vehicle' means a dedicated sp ecial purpose vehicle wh ich has instruments to 
measure the vertical and the longitudinal forces on one test tyre during braking. 
3. GENERAL  TEST  CONDITIONS 
3.1 Track characteristics 
The test track shall have the following characteristics: 
(1) The surface shall have a dense asphalt surf ace with a uniform grad ient of not more 
than 2 % and shall not deviate more than 6 mm when tested with a 3 m straight edge. 
(2) The surface shall have a pavement of uniform age, composition, and wear. The test 
surface shall be free of loose material and foreign deposits. 
(3) The maximum chipping size shall be from 8 mm to 13 mm. (4) The texture depth as measured by a sand patch shall be 0,7 ± 0,3 mm. It shall be 
measured every 10 metres in accordance with ASTM E 965-96 (Reapproved 2001). 
(5) The wetted frictional properties of the surf ace shall be measured with either method 
(a) or (b) in section 3.2. 
3.2  Methods to measure the wetted frictional properties of the surface 
(a) British Pendulum Number (BPN) method 
The British Pendulum Number method shal l be as defined in ASTM E 303-93 
(Reapproved in 2003). 
Pad rubber component formula tion and physical properties sh all be as specified in 
ASTM E 501-06. 
The averaged British Pendulum Number (BPN) shall be between 42 and 60 BPN 
after temperature correction as follows. 
BPN shall be corrected by the wetted road surface temperature. Unless temperature 
correction recommendations are indicated by the British pendulum  manufacturer, the 
following formula is used: 
BPN = BPN(measured value) + temperature correction EN 6   EN temperature correction = -0,001 8 t 2 + 0,34 t - 6,1 
where t is the wetted road surface temp erature in degrees Celsius. 
Effects of slider pad wear: The pad shall be removed for maximum wear when the 
wear on the striking edge of th e slider reaches 3,2 mm in th e plane of the slider or 1,6 
mm vertical to it in accordance with s ection 5.2.2 and Figure 3 of ASTM E 303-93 
(Reapproved 2003). 
For the purpose of checking track surface BPN consistency for the measurement of 
wet grip on an instrumented passenger car : the BPN values of the test track should 
not vary over the enti re stopping distance so as to decrease the dispersion of test 
results. The wetted frictional properties of th e surface shall be measured five times at 
each point of the BPN measurement every 10 meters and the coefficient of variation 
of the averaged BPN shall not exceed 10 %. 
(b) ASTM E 1136 Standard Referen ce Test Tyre (SRTT14”) method 
By derogation with point (4) of section 2, th is method uses the reference tyre that has 
the characteristics indicate d in ASTM E 1136-93 (Reapprov ed 2008) and referred to 
as SRTT14”2. 
The average peak braking coefficient ( µpeak,ave ) of the SRTT14” shall be 0,7 ± 0,1 at 
65 km/h. 
The average peak braking coefficient ( µpeak,ave ) of the SRTT14” shall be corrected by 
the wetted road surface temperature as follows: 
 peak braking coefficient ( µpeak,ave )= peak braking coefficient (measured) + 
temperature correction 
temperature correction = 0,0035 x ( t - 20) 
where  t is the wetted road surface temp erature in degrees Celsius. 
3.3 Atmospheric conditions 
The wind conditions shall not interfere with  wetting of the surface (wind-shields are 
allowed). 
Both the wetted surface temperature and th e ambient temperature shall be between 
2°C and 20°C for snow tyres and 5°C and 35°C for normal tyres. 
The wetted surface temperature shall not vary during the test by more than 10°C. The ambient temperature must remain clos e to the wetted surface temperature; the 
difference between the ambient and the wett ed surface temperatures must be less 
than 10°C. 
                                                
 
2 The size of the ASTM E 1136 SRTT is P195/75R14 EN 7   EN 4. TESTING  METHODS  FOR  MEASURING  WET  GRIP 
For the calculation of the wet grip index (G ) of a candidate tyre, the wet grip braking 
performance of the candidate tyre is compared  to the wet grip braking performance of the 
reference tyre on a vehicle travelling straight ah ead on a wet, paved surface. It is measured 
with one of the following methods: 
– vehicle method consisting of testing a set of  tyres mounted on an instrumented passenger 
car; 
– testing method using a trailer to wed by a vehicle or a tyre test  vehicle, equipped with the 
test tyre(s). 
4.1 Testing method using an instrumented passenger car 
4.1.1 Principle The testing method covers a procedure for me asuring the deceleration performance of C1 
tyres during braking, using an instrumented pa ssenger car equipped with an Antilock Braking 
System (ABS), where 'instrumented passenger car'  means a passenger car that is fitted with 
the measuring equipment listed in section 4.1.2.2 for the purpose of this testing method. 
Starting with a defined initial speed, the brakes are applied ha rd enough on four wheels at the 
same time to activate the ABS. The average deceleration is calculated between two pre-
defined speeds.  
4.1.2 Equipment 
4.1.2.1 Vehicle 
Permitted modifications on the passenger car are as follows: – those allowing the number of tyre sizes that can be mounted on the vehicle to be increased; 
– those permitting automatic activation of the braking device to  be installed. 
Any other modification of the braking system is prohibited. 
4.1.2.2 Measuring equipment The vehicle shall be fitted with a sensor su itable for measuring speed on a wet surface and 
distance covered between two speeds.  
To measure vehicle speed, a fift h wheel or non-contact speed-meas uring system shall be used. 
4.1.3 Conditioning of the test track and wetting condition  
The test track surface shall be watered at least ha lf an hour prior to testing in order to equalize 
the surface temperature and water temperat ure. External watering should be supplied 
continuously throughout testing. For the whole tes ting area, the water depth shall be 1.0 ± 0.5 
mm. 
The test track should then be conditioned by conduc ting at least ten test runs with tyres not 
involved in the test programme at 90 km/h. EN 8   EN 4.1.4 Tyres and rims 
4.1.4.1 Tyre preparation and break-in 
The test tyres shall be trimmed to remove a ll protuberances on the tread surface caused by 
mould air vents or flashes at mould junctions. 
The test tyres shall be mounted on the te st 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 te sting. They should be shielded from 
the sun to avoid excessive heating by solar radiation. 
For tyre break-in, two braki ng runs shall be performed. 
4.1.4.2 Tyre load The static load on each front axle tyre shall li e between 60 % and 90 % of the tested tyre load 
capacity. Tyre loads on the same axle should not differ by more than 10 %. 
4.1.4.3 Tyre inflation pressure On the front and rear axles, the inflation pre ssures shall be 220 kPa (f or standard- and extra-
load tyres). The tyre pressure should be checked  just prior to testing at ambient temperature 
and adjusted if required. 
4.1.5 Procedure 
4.1.5.1 Test run 
The following test procedure applies for each test run: (1) The passenger car is driven in a straight line up to 85 ± 2 km/h. 
(2) Once the passenger car has reached 85 ± 2 km/ h, the brakes are always activated at the 
same place on the test track referred to as 'braki ng starting point', with a longitudinal tolerance 
of 5 m and a transverse tolerance of 0,5 m. 
(3) The brakes are activated eith er automatically or manually.  
(i) The automatic activation of the brakes  is performed by means of a detection 
system made of two parts, one indexed to the test track and one on board the 
passenger car.  
(ii) The manual activation of the brakes depends on the type of transmission as 
follows. In both cases, a minimum of  600 N pedal efforts is required. 
 For manual transmission, the driver s hould release the clutch and depress the 
brake pedal sharply, holding it down as  long as necessary to perform the 
measurement. EN 9   EN  For automatic transmission, the driver should select neutral gear and then 
depress the brake pedal sh arply, holding it down as  long as necessary to 
perform the measurement. 
(4) The average decelera tion is calculated between 80 km/h and 20 km/h. 
If any of the specifications listed above (including speed tolerance, longitudinal and 
transverse tolerance for the braking starting poi nt, and braking time) are not met when a test 
run is made, the measurement is discarded and a new test run is made. 
4.1.5.2 Test cycle A number of test runs are made  in order to measure the wet gr ip index of a set of candidate 
tyres (T) according to the following procedure, whereby each test run shall be made in the same direction and up to three different set of  candidate tyres may be  measured within the 
same test cycle: 
(1) First, the set of reference tyres are m ounted on the instrumented passenger car.  
(2) After at least three valid measurements have been made in accordance with section 
4.1.5.1, the set of reference tyres is repl aced by a set of candidate tyres.  
(3) After six valid measurements of the candi date tyres are performed, two more set of 
candidate tyres may be measured.  
(4) The test cycle is closed by three more valid  measurements of the same set of reference 
tyres as at the beginning of the test cycle.  
EXAMPLES: – The run order for a test cycle of three sets of candidate tyres (T1 to T3) plus a set of 
reference tyres (R) would be the following: 
R-T1-T2-T3-R 
– The run order for a test cycle of five sets of candidate tyres (T1 to T5) plus a set of 
reference tyres (R) would be the following: 
R-T1-T2-T3-R-T4-T5-R 
4.1.6 Processing of measurement results 
4.1.6.1 Calculation of the average deceleration ( AD) 
The average deceleration ( AD) is calculated for each valid test run in m.s
-2 as follows:  
dS SADi f
22 2−=
 
where: 
Sf is the final speed in m·s-1; Sf = 20 km/h = 5.556 m.s-1 EN 10   EN Si is the initial speed in m·s-1; Si = 80 km/h = 22.222 m.s-1 
d is the distance covered in m between Si and Sf. 
4.1.6.2 Validation of results The AD coefficient of variation is calculated as follows: 
(Standard Deviation / Average) x 100. 
For the reference tyres (R): If the AD coefficient of variation of  any two consecutive groups of 
three test runs of the reference tyre set is higher than 3 %, a ll data should be discarded and the 
test repeated for all test tyres (the candidate tyres and the reference tyres). 
For the candidate tyres (T): The AD coefficients of variation ar e calculated for each candidate 
tyre set. If one coefficient of variation is great er than 3 %, the data should be discarded and 
the test repeated for that candidate tyre set. 
4.1.6.3 Calculation of adju sted average deceleration ( Ra) 
The average deceleration ( AD) of the reference tyre set used for the calculation of its braking 
force coefficient is adjusted according to the po sitioning of each candidate tyre set in a given 
test cycle.  
This adjusted AD of the reference tyre ( Ra) is calculated in m.s
-2 in accordance with table 1 
where R1 is the average of the AD values in the first test of the reference tyre set (R) and R2 is 
the average of the AD values in the second test of th e same reference tyre set (R). 
Table 1 
Number of sets of candidate 
tyres within one test cycle Set of candidate tyres Ra 
1 
(R1-T1-R 2) T1 Ra = 1/2 (R 1 + R 2) 
T1 Ra = 2/3 R 1 + 1/3 R 2 2 
(R1-T1-T2-R 2) T2 Ra = 1/3 R 1 + 2/3 R 2 
T1 Ra = 3/4 R 1 + 1/4 R 2 
T2 Ra = 1/2 (R 1 +R 2) 3 
(R1-T1-T2-T3-R 2) 
T3 Ra = 1/4 R 1 + 3/4 R 2 
 EN 11   EN 4.1.6.4 Calculation of the braking force coefficient ( BFC ) 
The braking force coefficient ( BFC ) is calculated for a braking on the two axles according to 
Table 2 where Ta (a = 1, 2 or 3) is the average of the AD values for each candidate tyre (T) set 
that is part of a test cycle. 
Table 2 
Test Tyre Braking force coefficient 
Reference tyre BFC(R )= │Ra/g│ 
Candidate tyre  BFC(T )= │Ta/g│ 
g is the acceleration due to gravity, g= 9,81 m·s-2 
 
4.1.6.5 Calculation of the wet grip  index of the candidate tyre  
The wet grip index of the candidate tyre ( G(T) ) is calculated as follows: 
2
00 10 0,1)()() ( 125)()()(−×⎥
⎦⎤
⎢
⎣⎡
⎟⎟
⎠⎞
⎜⎜
⎝⎛− ×+−×+× =R BFCR BFCb ttaR BFCT BFCTG
 
where: 
– t is the measured wet surface temperature in  degree Celsius when the candidate tyre (T) is 
tested  
– t0 is the wet surface reference temperature condition, t0=20°C for normal tyres and t0=10°C 
for snow tyres 
– BFC(R 0) is the braking force coefficient for the reference tyre in the reference conditions, 
BFC(R 0) = 0,68 
– a= -0,4232 and b = -8,297 for normal tyres, a = 0,7721 and b = 31,18 for snow tyres 
4.1.7 Wet grip performance comparison betw een a candidate tyre and a reference tyre 
using a control tyre 
4.1.7.1 General 
Where the candidate tyre size is si gnificantly different from that of the reference tyre, a direct 
comparison on the same instrumented passenger car  may not be possible. This testing method 
uses an intermediate tyre, hereinafter called the co ntrol tyre as defined in point 5 of section 2. 
4.1.7.2 Principle of the approach The principle is the use of a c ontrol tyre set and two different instrumented passenger cars for 
the test cycle of a candidate tyre set in  comparison with a reference tyre set. EN 12   EN One instrumented passenger car is fitted with the reference tyre set followed by the control 
tyre set, the other with the control tyre set followed by the candidate tyre set.  
The specifications listed in secti ons 4.1.2. to 4.1.4 apply.  
The first test cycle is a comparison between the control tyre set and the reference tyre set. 
The second test cycle is a comparison between the candidate tyre set and the control tyre set. 
It is done on the same test tr ack and during the same day as the first test cycle. The wetted 
surface temperature shall be within  ± 5 °C of the temperature of the first test cycle. The same 
control tyre set shall be used for the first and the second test cycles. 
The wet grip performance inde x of the candidate tyre ( G(T)) is calculated as follows: 
G(T)  = G1 × G2 
where: –
 G1 is the relative wet grip index of the control tyre (C) compared to the reference tyre (R) 
calculated as follows: 
2
00 1 10 0,1)()() ( 125)()(−×⎥
⎦⎤
⎢
⎣⎡
⎟⎟
⎠⎞
⎜⎜
⎝⎛− ×+−×+× =R BFCR BFCb ttaR BFCC BFCG
 
– G2 is the relative wet grip index of the candidate tyre (T) compared to the control tyre (C) 
calculated as follows: 
)()(
2C BFCT BFCG=
 
4.1.7.3 Storage and preservation 
It is necessary that all the tyres of a control tyre set have been stored in the same conditions. 
As soon as the control tyre set has been test ed in comparison with the reference tyre, the 
specific storage conditions defined in ASTM E 1136-93 (Reapproved 2008) shall be applied. 
4.1.7.4 Replacement of refere nce tyres and control tyres 
When irregular wear or damage results from tests,  or when wear influences the test results, the 
use of the tyre shall be discontinued. 
4.2 Testing method using a trailer towed by a vehicle or a tyre test vehicle 
4.2.1 Principle 
The measurements are conducted on test ty res mounted on a traile r towed by a vehicle 
(hereafter referred to as tow vehi cle) 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. EN 13   EN 4.2.2 Equipment 
4.2.2.1 Tow vehicle and tra iler or tyre test vehicle 
– The tow vehicle or the tyre test vehicle sh all 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 wate r to supply the road surface wetting system, 
unless external watering is used; 
(iii) recording equipment to record signal s from transducers installed at the test 
position and to monitor water application rate if the self-w atering option is 
used. 
–
 The limiting change of toe and camber for the te st position shall be within ± 0,5° with 
maximum vertical load. Suspension arms a nd bushings shall have sufficient rigidity 
necessary to minimize free play and ensure  compliance under appl ication 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 for ce as specified in section 4.2.7.1. 
– The trailer or the tyre test vehicle shall be designed to acco mmodate 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 –
 The test wheel position on the trailer or the tyre test vehicle shall be equipped with a 
rotational wheel velocity measuring system an d 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 ambi ent 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; EN 14   EN – Vehicle speed: To measure ve hicle 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 inte rface as a result of brake appl ication within a range from 0 
% to at least 125 % of the applied vertical load. The transducer design and location shall 
minimize inertial effects and vibra tion-induced mechanical resonance. 
– Vertical load: The vertical load-measuring trans ducer shall measure the vertical load at the 
test position during brake application. The tran sducer shall have the same specifications as 
described previously. 
– Signal conditioning and recording system: All signal conditioning and recording 
equipment shall provide linear output with nece ssary 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 rati o shall be at least 20/1. 
(iii) The gain shall be sufficient to pe rmit full-scale display for full-scale input 
signal level. 
(iv) The input impedance shall be at least ten times larg er 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 
The test track should be condi tioned by conducting at least te n test runs with tyres not 
involved in the test program at 65 ± 2 km/h. 
4.2.4 Wetting conditions 
The tow vehicle and trailer or the tyre test  vehicle may be opti onally equipped with a 
pavement-wetting system, less the storage tank, which, in the cas e of the traile r, 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 design ed 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 positi on shall ensure that the water jets are directed towards the 
test tyre and pointed towards the pa vement 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 he ight required to clear 
obstacles which the tester is expected to en counter, but in no case more than 100 mm above 
the pavement. EN 15   EN 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 deliv ery 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 sh all 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 
4.2.5.1 Tyre preparation and break-in 
The test tyres shall be trimmed to remove a ll 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 h eating 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 The test load on the test tyre is 75 ± 5 % of the test tyre load capacity. 
4.2.5.3 Tyre inflation pressure 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 te mperature and adjusted 
if required.  
4.2.6 Preparation of the tow vehicle and trailer or the tyre test vehicle 
4.2.6.1 Trailer 
For one axle trailers, the hitch height and transverse position shall be adjusted
 once the test 
tyre has been loaded to the specified test lo ad 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 ax le of the traile r shall be at le ast ten times the 
“hitch height” or the “coupling (hitch) height”. 
4.2.6.2 Instrumentation and equipment Install the fifth wheel, when used, in accordance with the manufacturer’s  specifications and 
locate it as near as possible to the mid-track positi on of the tow trailer or the tyre test vehicle. EN 16   EN 4.2.7 Procedure 
4.2.7.1 Test run 
The following procedure applies for each test run: –
 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. 
– The recording system is launched. 
– Water is delivered to the pavement ahead of th e test tyre approximately 0,5 s prior to brake 
application (for internal watering system). 
– The trailer brakes are activat ed within 2 metres of a meas urement 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 brak ing application shall be such that the time interval between 
initial application of force a nd peak longitudinal force is in the range 0,2 s to 0,5 s.  
– The recording system is stopped. 
4.2.7.2 Test cycle A number of test runs are made in order to m easure the wet grip index of the candidate tyre 
(T) according to the following procedure, wher eby 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. 
–
 First, the reference tyre is tested.  
– After at least six valid measurements are perf ormed in accordance with section 4.2.7.1, the 
reference tyre is replaced by the candidate tyre.  
– After six valid measurements of the candidate  tyre are performed,  two more candidate 
tyres may be measured.  
– The test cycle is closed by six more valid measurements of the same reference tyre as at the 
beginning of the test cycle.  
EXAMPLES: 
– 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 EN 17   EN 4.2.8 Processing of measurement results 
4.2.8.1 Calculation of the p eak braking force coefficient 
The tyre peak braking force coefficient ( µpeak) is the highest value of µ(t) before lockup occurs 
calculated as follows for each test run. Analog signals should be filtered to remove noise. 
Digitally recorded signals must be filtered using a moving average technique. 
)()()(tfvtfht=µ  
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 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 
(µpeak) of the reference tyre is higher than 5 %,  all data should be di scarded 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 
(µpeak) is calculated for each candidate tyre. If one co efficient of variation is greater than 5 %, 
the data should be discarded and the te st repeated for this candidate tyre. 
4.2.8.3 Calculation of the adjusted  average peak braking coefficient 
The average peak braking coefficient of the re ference 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 coefficient of the reference tyre ( Ra) is calculated in 
accordance with table 1 where R 1 is the average peak tyre braking coefficient in the first test 
of the reference tyre (R) and R2 is the average peak ty re 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 
(R1-T1-R 2) T1 Ra = 1/2 (R 1 + R 2) EN 18   EN T1 Ra = 2/3 R 1 + 1/3 R 2 2 
(R1-T1-T2-R 2) T2 Ra = 1/3 R 1 + 2/3 R 2 
T1 Ra = 3/4 R 1 + 1/4 R 2 
T2 Ra = 1/2 (R 1 +R 2) 3 
(R1-T1-T2-T3-R 2) 
T3 Ra = 1/4 R 1 + 3/4 R 2 
4.2.8.4 Calculation of the average peak tyre braking coefficient ( µpeak,ave )  
The average value of the peak tyre braking coefficients ( µpeak,ave ) is calculated according to 
table 4 whereby Ta (a= 1, 2 or 3) is the average of the peak braking coefficients measured for 
one candidate tyre within one test cycle. 
Table 4 
Test tyre µpeak,ave  
Reference tyre µpeak,ave (R)=Ra as per Table 3 
Candidate tyre µpeak,ave (T) = Ta 
 
4.2.8.5 Calculation of the wet grip  index of the candidate tyre  
The wet grip index of the candidate tyre ( G(T))  is calculated as follows: 
 
2
0 ,,
0
,,10 0,1)()() ( 125)()()(−×
⎥⎥
⎦⎤
⎢⎢
⎣⎡
⎟⎟
⎠⎞
⎜⎜
⎝⎛
− ×+−×+× =RRb ttaRTTG
ave peakave peak
ave peakave peak
µµ
µµ 
 
where: 
– t is the measured wet surface temperature in  degree Celsius when the candidate tyre (T) is 
tested 
– t0 is the wet surface reference temperature condition  
– t0=20°C for normal tyres  t0=10°C for snow tyres 
– µpeak,ave (R0) = 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 EN 19   EN Annex A: Test reports exam ples of wet grip index  
EXAMPLE 1: Test report of wet gr ip index using trailer method 
Test report number: 
Type of road surface: 
µ peak (SRTT14” E 1136):  
Speed (km/h): Test date: 
Texture depth (mm): 
BPN: 
Water depth (mm): 
 
No. 1 2 3 4 5 6 7 8 9 10 
S i z e            
S e r v i c e  d e s c r i p t i o n            
T y r e  i d e n t i f i c a t i o n            
R i m            
P a t t e r n            
L o a d  ( k g )            
P r e s s u r e             
µp e a k  1            
 2            
 3            
 4            
 5            
 6            
 7            
 8            
Average            
Standard deviation σ           
(σ/average) ≤5%           
Ra, Adjusted            
W e t  g r i p  i n d e x            
Surface temp.           
A m b i e n t  t e m p .            
R e m a r k s            EN 20   EN EXAMPLE 2: Test report of wet gr ip index using passenger car method 
 Driver: Test date: 
Track:  
Texture depth (mm): 
BPN:  
Water de pth (mm): Passenger car: 
Brand: 
Model: 
Type:Initial speed (km/h): 
Final speed (km/h): 
 
No. 1 2 3 4 5 
Brand Uniroyal TYRE B TYRE C TYRE D Uniroyal 
Pattern ASTM F 2493
SRTT16” PATTERN B PATTERN C PATTERN D ASTM F 2493 
SRTT16” 
Size P225/60R16 SIZE B SIZE C SIZE D P225/60R16 
Service description 97S LI/SS LI/SS LI/SS 97S 
Tyre identification XXXXXXXXX  YYYYYYYYY  ZZZZZZZZZ  NNNNNNNNN XXXXXXXXX  
Rim      
Front axle pressure (bar)      
Rear axle pressure (bar)      
Front axle load (kg)      
Wet surface tem p (°C)   
Ambient temp (°C)      
 Braking 
distance 
(m)Average 
deceleration 
(m/s2)Braking
distance
(m)Average 
deceleration
(m/s2)Braking
distance
(m)Average 
deceleration
(m/s2)Braking 
distance 
(m)Average 
deceleration 
(m/s2)Braking 
distance 
(m)Average 
deceleration 
(m/s2)
Measurement 1           
 2           
 3           
 4           
 5           
 6           
 7           
 8           
 9           
 10           
Average AD (m/s2)           
Standard deviation (m/s2)           
Validation of results 
Coeff. of variation (%) < 3 %           
Adjusted average AD of ref. tyre: Ra 
(m/s2)           
BFC(R) reference tyre (SRTT16”)           
BFC(T) candidate tyre           
Wet grip index (%)           
"