SECURITY & ADHERENCE TESTING Joël Foucard

1. SECURITY & ADHERENCE TESTING Joël Foucard

2. ADHERENCE TESTING : MICHELIN STRATEGY ROAD CHARACTERISTICS ADHERENCE MECHANISMS ACCIDENT ANALYSIS MICHELIN TEST TRACKS ADHERENCE AND SAFETY WET GRIP REGULATION EURONCAP

3. Microtexture : 0,1µm to 10µm height Macrotexture : 10µm to 1mm height ROADS CHARACTERISTICS • PARAMETERS :

4. Sand Depth (mm) : mean texture depth ROADS CHARACTERISTICS • MACROTEXTURE : Direct measurement : from diameter of sand mark Indirect measurment : computation from laser texture measurement

5. SCRIM vehicle : transversal friction coefficient (CFT) on wet road with a motorcycle tire at 20 deg angle ROADS CHARACTERISTICS • MICROTEXTURE :

6. ROADS CHARACTERISTICS • FRENCH ROADS DISTRIBUTION : • Data from transport department : Microtexture : CFT CFT distribution is confidential : cannot be given with this detail level Macrotexture : Sand Depth

7. Microtexture : CFT Macrotexture : Sand Depth ROADS CHARACTERISTICS • FRENCH ROADS DISTRIBUTION : • Data from transportation ministry :

8. ADHERENCE TESTING : MICHELIN STRATEGY ROAD CHARACTERISTICS ADHERENCE MECHANISMS ACCIDENT ANALYSIS MICHELIN TEST TRACKS ADHERENCE AND SAFETY WET GRIP REGULATION EURONCAP

9. Area 4 Area 3 Area 2 Area 1 ADHERENCE MECHANISMS • MECHANISMS : • Main mechanisms only :

10. ADHERENCE MECHANISMS • HYDROPLANNING : • Phenomenon : • Loss of contact due to hydrodynamic effects , dependent on speed, pressure , water height , pattern depth • Key actors : • Tire : • Tread pattern • Pressure map in contact patch • Road : • Macrotexture and banking • Absence of ruts

11. ADHERENCE MECHANISMS • VISCOPLANNING : • Phenomenon : • Squeezing of water between a flat surface and rubber due to water viscosity, as soon as the layer thickness is < 10 µm hf : final height hi : initial height S : surface P : pressure h : fluid viscosity • Key actors : • Road : • Microtexture to puncture the water film • Tire : • Eliminate water • Create high local pressure Bad good

12. Rubber Ground ADHERENCE MECHANISMS • INDENTATION : • Phenomenon : • On the top of any indenter , delay between stresses and strains due to rubber hysteretic losses . • Appears at all scales of indenters sizes and associated excitation frequencies • Key actors : • Tire : • Viscoelastic properties under high frequency (104 to 107 Hz) and high strain • Road : • Texture on a large band of indenter sizes and associated excitation frequencies

13. ADHERENCE MECHANISMS • BRAKING DISTANCE ON WET ROAD : • Conditions : 80 to 10 km/h ; Water thickness = 1 mm ; New tire • Dominant mechanisms under these conditions : • Hydroplanning is neglectable • Viscoplanning is dominant on low-micro & low-macro surfaces . Its impact may be emphasised on dirty/polluted roads • Indentation is dominant on almost all clean roads Visco-planning on dirty roads Visco-planning on clean roads

14. Significant µ loss due to Hydro function of tiresize and wear level No µ loss due to Hydro ADHERENCE MECHANISMS • BRAKING DISTANCE ON WET ROAD : • Max rain intensity (2% of the total rain time) : • Measurement of water height above the indenter summit (PREDIT program) • 1mm is a maximum value for a good road . More than 1mm occurs in pools and ruts

15. ADHERENCE MECHANISMS • BRAKING DISTANCE ON WET ROAD : • Conditions : speed , tread pattern depth , water height • Hydroplanning is a significant mechanism in worn tires braking distance

16. ADHERENCE TESTING : MICHELIN STRATEGY ROAD CHARACTERISTICS ADHERENCE MECHANISMS ACCIDENT ANALYSIS MICHELIN TEST TRACKS ADHERENCE AND SAFETY WET GRIP REGULATION EURONCAP

17. ACCIDENT ANALYSIS • GLOBAL FIGURES : FRANCE • INRETS DATA ON 2001 PERIOD • Focus on fatalities • Total of 7720 people killed Who Where Note • : Trucks • = 5,2% of traffic • = 5% of injury accidents • = 13% of fatalities • (2) : Urban areas : • = 1/4 of fatalities • = 2/3 of injury accidents

18. ACCIDENT ANALYSIS • TYPE OF ACCIDENT : Lateral loss of control : 55% Longitudinal loss of control : 32%

19. ACCIDENT ANALYSIS • RAIN CONDITION : • Average rain duration in France : 9,3% • Known rain effects : • No pedestrian and few cycles and motorcycles • Sensible reduction of passenger cars traffic • Estimation of specialists : 3 times more accident / km in rain condition than in normal dry condition

20. ACCIDENT ANALYSIS • DAMP ROAD CONDITION : • As recorded in police report , do not take into account very thin layers of water such as : • Moisture retained by road salt during winter • Morning dew • Damp surface condition : rain condition + drying time • Depending on sources , damp condition = 25% to 40% • Generic data files do not allow to estimate the severity of damp condition versus dry condition

21. µ=0,6 ACCIDENT ANALYSIS • ROAD WEAR : • Impact on accidents in wet condition • The Accident risk level increases as the µ level decreases

22. ACCIDENT ANALYSIS • ROAD POLLUTION : • Impact on accidents in wet condition • 10 years statistics : rain is more severe in fall than in the rest of the year . • First rain after a long period of dryness is more severe because it makes a viscous mixture with chemicals (gasolin , grease , vegetal origin , …) deposited in the bottom of texture • Viscoplanning is extremely unlikely on clean road but may have a significant action on polluted roads

23. Range of adherence used by customers in normal conditions µ coefficient Range of max potential offered by tire/road 1,0 New road 0,8 Worn road 0,6 Polluted road Snow 0,4 Ice 0,2 0 Winter Wet Dry ACCIDENT ANALYSIS • CUSTOMER NEED VS AVAILABLE POTENTIAL • A margin is available on dry roads for emergency manoeuvers . But there is no such margin on lowest grip wet roads nor in winter .

24. ADHERENCE TESTING : MICHELIN STRATEGY ROAD CHARACTERISTICS ADHERENCE MECHANISMS ACCIDENT ANALYSIS MICHELIN TEST TRACKS ADHERENCE AND SAFETY WET GRIP REGULATION EURONCAP

25. MICHELIN TEST TRACKS • PASSENGER CAR TRACKS CHARACTERISTICS : • Longitudinal (braking) • L1 : min. threshold • L2 & L3 : axes of product improvement • L4 : research only Microtexture : CFT T2 T3 L2 • Transversal • - T1 : circular ring , min. threshold • T2 : circular ring ,axis of product improvement • T3 : wet handling track , axis of product improvement L3 L4 T1 L1 Macrotexture : Sand Depth • Michelin test requirements adapted to our understanding of customer risks

26. ADHERENCE TESTING : MICHELIN STRATEGY ROAD CHARACTERISTICS ADHERENCE MECHANISMS ACCIDENT ANALYSIS MICHELIN TEST TRACKS ADHERENCE AND SAFETY WET GRIP REGULATION EURONCAP

27. ADHERENCE AND SAFETY • ADHERENCE PERFORMANCE BUILDING : Road & Weather conditions Pneumatic Brakes + Chassis Electronic Systems Customer Reaction Ground contact Potential Fraction of potential use X Fraction of potential use Braking potential X

28. ADHERENCE AND SAFETY • ABS IMPACT ON SAFETY : • Scope : • 7 GM vehicles models equipped w / wo ABS • 5 states in USA • 1 year time period • Main résults on casualty accidents : • No significant impact on overall number • Slight increase on dry road due to speed increase with ABS , increase of accident severity • 12% reduction on wet roads • 22% reduction of accidents involving pedestrian • GM study , SIA Paper N° 98-S2-0-12 • Improving braking potential pays more on wet than on dry roads

29. ADHERENCE AND SAFETY • ESP IMPACT ON SAFETY : • Scope : • Sweden 2000-2002 • MB, BMW, Audi-VW, w/wo ESP . ABS on all vehicles • 1 year time period • Main résults on casualty accidents : • 22% reduction on overall number • 9% reduction on dry roads • 31% reduction on wet roads • 38% reduction on snow & ice • Swedish National Administration , Paper N°261 • Improving braking potential pays more on low traction roads than on high traction roads

30. ADHERENCE TESTING : MICHELIN STRATEGY ROADS CHARACTERISTICS ADHERENCE MECHANISMS ACCIDENTS ANALYSIS MICHELIN TEST TRACKS ADHERENCE AND SAFETY WET GRIP REGULATION EURONCAP

31. WET GRIP REGULATION • 2 APPROVED METHODS • Method using a standard vehicule : braking distance • Method using a trailer : µ(G) curve • EVALUATION IN RELATIVE • Relative performance basis : comparison to a reference tyre : SRTT E1136 (195/75R14) • TRACK GENERAL SPECIFICATION • Sand depth : 0.7 + 0.3 mm • BPN : 50 + 10 • TEST TEMPERATURE • Wetted surface temperature within 20°C +/- 15°C • Temperature variation during test < 10°C

32. WET GRIP REGULATION • VEHICLE METHOD : • Standard model passenger car , 4 wheel ABS braking , suitable to accept a wide variety of tire sizes • Static tyre load : from 60% to 90% of the tyre load capacity • Measurement of the average deceleration of a vehicle between two given speeds • Initial speed : 80 km/h • Final speed : 20 km/h • Water depth : flooded between 0,5 and 1,5 mm

33. WET GRIP REGULATION • VEHICULE METHOD : • Unique reference tire • Use of control tire to deal with tire size differences • (Test/Reference) = (Test/Control) x (Control/Reference) Reference tyre Vehicle 1 C1 C2 …. Ck : control tyres x x x x x x x x x x x x x x x x x x x x x x x x x x x Vehicle 2

34. Microtexture : CFT 100 90 80 70 60 50 40 30 20 Norme wet grip 10 0 -10 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 0 Microtexture : BPN Macrotexture : Sand Depth 40 to 60 0,4 to 1,0 WET GRIP REGULATION • TRACK SPECIFICATION :

35. ADHERENCE TESTING : MICHELIN STRATEGY ROADS CHARACTERISTICS ADHERENCE MECHANISMS ACCIDENTS ANALYSIS MICHELIN TEST TRACKS ADHERENCE AND SAFETY WET GRIP REGULATION EURONCAP

36. Microtexture (BPN) Excellence area of stiff tread pattern Stone mastic Asphalt Excellence area of soft tread pattern (like winter tread pattern) Basalt Wet grip regulation Macrotexture (Sand Depth) EURONCAP • TRACK SPECIFICATION • Wet adherence issue The risks from our understanding of EuroNCAP project : • If the surface choice is confirmed (against the pneumatic industry expertise) , this could handicap the development of the best solutions for low adherence roads

37. EURONCAP • ABSOLUTE RANKING • The track surface evolution is not compatible with absolute braking distance ranking