Stop Distances for Ten Studless Winter Tires

TECHNICAL REPORT

Division of Machine Elements Division of Structural Engineering,

ISSN: 1402-1536 ISBN 978-91-7439-041-4 Stop distancesOctober 9, 2009, rev 0.9 Luleå University of Technology 2009 for ten studlessStop distances winter tires for ten studless winter tires

Niclas Engströma Henrik Andrénb Roland Larssona and Lennart Franssonb

aDivision of Machine Elements, Luleå University of Technology bDivision of Structural Engineering, Luleå University of Technology Niclas Engström HenrikSupported by: Andrén Kempe foundations, I2, CASTTRoland and the SwedishLarsson Road Administration. Lennart Fransson

Academic partners:

October 9, 2009, rev 0.9 October 9, 2009, rev 0.9 StopStop distances distances forfor ten ten studless studless winter winter tires tires

a b a b NiclasNiclas Engström Engströma HenrikHenrik Andrén Andrénb RolandRoland Larsson Larssona and Lennartand Lennart Fransson Franssonb a a Division of Machine Elements, Luleå University of Technology Divisionb of Machine Elements, Luleå University of Technology bDivisionDivision of Structural of Structural Engineering, Engineering, Luleå Luleå University University of Technology of Technology

Supported by: Supported by: Kempe foundations, I2, CASTT and the Swedish Road Administration. Kempe foundations, I2, CASTT and the Swedish Road Administration.

Academic partners: Academic partners: ISSN: 1402-1536 ISBN 978-91-7439-041-4

Luleå 2009 www.ltu.se Preface

This report contains stop distance measurements performed during winter 2008/2009 at Ice- Maker´s test tracks on lake Kakel, Arjeplog. Luleå University of Technology, the Divisions of Machine Elements and Structural Engineering are thrilled that we have been given the oppor- tunity to be a part of these tests. We would like to thank the Swedish Road Administration, Kempe foundation, I2 and CASTT for funding of these tests. We also would like to thank Mikael Nybacka and Janne Granström at LTU for their help with measuring systems. A special thanks to Carl-Henrik Ulegård at the Swedish Road Administration for all his help during the entire project.

Luleå June 2009

Niclas Engström, Henrik Andrén, Lennart Fransson and Roland Larsson Contents

1 Executive summary 3

2 Introduction 5

3 Goals and objectives 6

4 Methodology 7 4.1 Calibration ...... 9 4.2 Conditions during tests ...... 9 4.3 Data presentation ...... 11

5 Results 12 5.1 Brushed old polished ice, March 10, 2009 ...... 12 5.2 Brushed old polished ice, February 11, 2009 ...... 14 5.3 Brushed old polished ice, February 12, 2009 ...... 15 5.3.1 Rough old system 2000 ice, February 11, 2009 ...... 16

6 Discussion 19

7 Conclusions 21

List of Figures 23

List of Tables 24

A Tires 25

B Vehicles 28 B.1 Vehicles 2009-02-09–2009-02-13 ...... 28 B.2 Vehicles 2009-03-09–2009-03-10 ...... 29

C V-Box3i 30 C.1 Speciﬁcation ...... 31 C.2 Certiﬁcates ...... 32

1 D Deceleration 34 D.1 Brushed old polished ice, March 10 ...... 34 D.2 Brushed old polished ice, Februrary 11-12 ...... 35 D.3 Rough old system 2000 ice, February 11 ...... 35

E Shortest stop distances 37 E.1 Brushed old polished ice during March 10, 2009 ...... 37 E.2 Brushed old polished ice during February 11, 2009 ...... 38 E.3 Brushed old polished ice during February 12, 2009 ...... 39 E.4 Rough old system 2000 ice during February 11, 2009 ...... 40

F Theory 42 F.1 Basic kinetics ...... 42 F.2 Deceleration measurements ...... 43

2 Chapter 1

Executive summary

In this report we highlight stop distance and roadgrip differences for ten sets of studless winter tires. There is a need to evaluate performance of winter tires and illustrate to the public that there are differences between winter tires. Some are made for northern Europe, some for central Europe and some for other parts of the world where special conditions and regulations apply. We also see a need to relate roadgrip measurements with different conditions. This to make distributed roadgrip information more clear to drivers related to their equipment. We must make drivers more aware that the tires on the vehicle are a very important factor when it comes to produce high and safe roadgrip. Stop distance tests are a well accepted method to measure performance of winter tires. In our opinion brushed old polished ice is a low grip surface that are relevant to test roadgrip on. The test track section with brushed old polished ice was roughly 100 m long and 10 m wide. The stop distance brake tests were performed from left to right. See Figure 1.1.

Test track layout Brake activation Brushed old polished ice marker

Vehicle tire paths 100 m 5 m

Figure 1.1: Test track Layout during stop distance measurements on Brushed old Polished Ice.

Stop distance measurements were also performed on system 2000 ice. This is a surface created with a grader equipped with “system 2000”, system 2000 is based on rounded hard metal teeth roughly 30 mm apart on the edge of a blade. This creates furrows in the ice, a rough surface. We found that roadgrip was high and very similar for all tires on system 2000 ice. Stop distances were short and we do not think that a surface like that are dangerous, as long as the driver adapts speed and distances to the available roadgrip.

3 CHAPTER 1. EXECUTIVE SUMMARY

Temperatures during all test ranged from -25 ◦C to -2.5 ◦C, however most tests were performed between -18 ◦C and -6 ◦C. If stop distance test becomes mandatory for winter tires and are made in a controlled environment then we recommend a temperature above -6 ◦C. Roadgrip decrease rapidly above that temperature as ice surfaces becomes slicker. km km km Speeds of 30 /h, 50 /h and some times 70 /h were used during the stop distance measurements. Different sizes of vehicles were used during the stop distance measurements, Volvo XC90, XC70, C30 and V70. No difference in stop distance related to car size was found. Tires for the tests were selected based on tests for magazines. We selected a test winning tire, a tire considered very bad for winter conditions and a tire we generally use in our tests as a reference tire. In our tests the test winning tire was actually performing below the norm on brushed old polished ice. Furthermore we found out that the “very bad” tire tested in one magazine [7] was classified for summer use by the manufacturer. The winter tires from this brand performed to the norm on brushed old polished ice and was considered an adequate winter tire. One tire outperformed all others on brushed old polished ice, it was made in Japan, where studless winter tires are the only kind allowed. It created at least 40 % higher roadgrip than any other tire. Tires are an important factor on winter roads. Tire information regarding performance on ice should be available to the public. We recommend that performance data is measured and presented by an independent entity. Tread depth is one important factor when evaluating conditions on a winter tire, however correct rubber compound is much more important than tread depth.

4 Chapter 2

Introduction

Correct winter tire selection is difficult for most vehicle owners, a correct choice depends on many factors. It has become even more important as studded tires are on a decline in many areas of Sweden, this is true, especially for highly populated areas around larger cities, see [6]. This could increase the risk if the vehicle owners have insufficient information to base their tire selection on. In the tire industry it is an established fact that tires are made for different tasks and/or areas of the world. This information is not readily available for most vehicle owners, the owner has to rely on information found in publications and recommendations from his local tire salesman. In general the information is not sufficient and there is a need for a classification system were tires are rated and recommended for a certain region. The most dangerous situation occurs when a vehicle owner purchase a tire made for a region south of his location. He will get a tire with significantly harder rubber compounds and thus a low level of hysteresis at cold temperatures, a.k.a. a glass transition point Tg, significantly higher than local temperatures. This will reduce the roadgrip and possibly lead to an incident. There have been research done on differences between different tires, see [5] and the results are clear, wrong rubber compound leads to a drastic reduction in roadgrip on ice and snow. This information must be available for all vehicle owners. It is strongly recommended that an tire index is created and maintained. The European New Car Assessment Programme “EURO NCAP” is one example of support to the buyer. “EURO NCAP” is a voluntary safety assessment program, however there are no tire selection section giving points for correct tire selection to a new vehicle. This is a significant weakness in the safety assessment. This report is a step in the process of creating an independent index. We are testing the stop distance for ten sets of tires. They are from five different brands and are studless. The bulk of the tests were performed on smooth brushed old polished ice. Temperatures were well below freezing, resulting in higher roadgrip than one would see with temperatures close to 0 ◦C. We will see some dramatic differences as one set was made for a special region of the world where studded tires are banned, namely Japan.

5 Chapter 3

Goals and objectives

The ultimate goal for this project is to decrease fatalities, injuries and damages on property in transportation activities during winter seasons. To accomplish this we need to increase the knowledge about winter tires and how they achieve roadgrip. One step toward the ultimate goal is to increase awareness about the importance of selecting winter tires. This is a goal that is possible to reach if the Swedish Road Administration, by themselves or with assistance of LTU, create a regulatory test that all winter tired must undergo to be approved for use in “winter conditions”, see [1]. Assistance from the Scandinavian Tire and Rim Association, AB Svensk Bilprovning, and VTI should be considered. Our objectives in testing studless winter tires were to build a case for a tire index and/or tire classification system, since there are significant differences in roadgrip depending on what type of winter tire one has mounted on a vehicle. We also wanted to see what impact vehicle weight has on stop distances. Tests on different surfaces were performed to find critical surface types where accidents are more likely to happen.

6 Chapter 4

Methodology

The basis of our tests are stop distance measurements on brushed old polished ice. Measurements were made with a total of ten sets of studless winter tires. Three sets came from two brands, two sets from one brand and one set from two brands. There were also one set old studded tires tested. Tires from a specific brand were not always the same model, as the two larger test vehicles were of sport utility vehicle (SUV) type and subsequently higher than regular cars. Tire manufacturers make stiffer tires for high vehicles to reduce the risk of tipping. For further tire information see Appendix A. Brake distance measurements were carried out during two periods, the first from 2009-02-09 to 2009-02-13 and the second period from 2009-03-09 to 2009-03-10. During the first period we used three Volvo cars, models were: XC90, XC70 and C30. For detailed information about the cars see Appendix B. Stop distance measurements were performed with two GPS (global positioning system) based V-Box3i 100 Hz units, see Appendix C for detailed information. To increase accuracy in the measurements, inertial motion sensors named IMU02 were connected to the V-Box3i units. In the software for the V-Box3i units we used an option to set speed dependent triggers to start and stop distance measurements. This trigger function will, when activated, start the measurement as soon as the speed decrease below a set value. For km km km these tests the speeds selected were 30 /h, 50 /h and sometimes 70 /h. During the second period we used a Volvo V70 and we tested with one set of tires from the previous period and one set that we wanted to complement the tests with. Tests with a rented Ford Mondeo equipped with used studded tires, F5 were done to see how old studded tires compare with new studless tires on brushed old polished ice. The test track section with brushed old polished ice was roughly 100 m long and 10 m wide. See Figure 4.1.

7 CHAPTER 4. METHODOLOGY

Test track layout Brake activation Brushed old polished ice marker

Vehicle tire paths 100 m 5 m

Figure 4.1: Test track Layout during brake tests on brushed old polished Ice. Driving direction is from right to left.

Preparation on the old polished ice was done by a local entrepreneur during early morning hours. The surface was brushed with a radial rotating brush, pushing the debris forward in the longitudinal1 direction of the track. A very strong fan blows the lose debris in the lateral direction, oﬀ the track. Before the tests we drove straight down the same path across the brake test area. This was done multiple times to get a polished surface with stable characteristics. To minimize the amount of debris on the test area, we drove in the same tire tracks outside the brake test area. See Figure 4.2. During the preparation phase we utilized higher speeds then during the test phase, this to ensure that conditions would be similar throughout the whole length of the test track.

Figure 4.2: Clear smooth polished ice made over rough system 2000 ice.

During some parts of the test a light snowfall fell in the test area. To ensure stationary conditions we drove with all vehicles to keep any lose snow from accumulating on the test surface. 1Longitudinal is in the track and vehicle direction, lateral meaning to the side.

8 4.1. CALIBRATION CHAPTER 4. METHODOLOGY

Data that was not repeated during at least three stop distance measurements were discarded. Instructions to the test drivers during the tests were:

• Use cruise control to maintain a slightly higher speed than target speed. • Drive along the same path as before. • Make smooth and small directional adjustments to maintain the right direction throughout the brake sequence.

• Brake ﬁrmly at the marker and apply ﬁrm pressure on the brake pedal until the car comes to a complete stop. • When the braking is completed drive away following initial direction without spinning the wheels.

• Follow a ﬁxed path back to the start position to minimize debris in the test area. • Repeat the sequence until at least three similar stop distances has been recorder for each speed.

Tire changes during the ﬁrst four test days were done at a local tire shop. This shop where located roughly ﬁve km from the test track. During the second test section of two days we changed wheels manually on lake Kakel.

4.1 Calibration

Calibration of the V-Box3i is done by the manufacturer. For certiﬁcates see Appendix C. A stand alone V-Box3i with a GPS antenna has a position accuracy of 3 m 95 % Circle of Error Probable (CPE); this means that the V-Box position measurement will fall into a circle with diameter 3 m 95 % of the time. During start up one should turn on the V-Box unit and park the vehicle for at least 10 minutes in a position that has as few obstacles as possible blocking km satellites, this is done to lock onto as many satellites as possible. Speed accuracy is 0.1 /h, for further details see Appendix C.

4.2 Conditions during tests

Conditions from 2009-02-09 to 2009-02-13 Tests were conducted in February, generally one of the colder months of the year, as is evident from Figure 4.3. Temperature and relative humidity was measured at ice level with a “USB-502 RH/Temperature Data Logger”, protected from direct sunlight by a screen. Mea- surement data was confirmed with a “Oregon Scientific Professional Wireless Weather Station WMR100N”. Figure 4.3 shows that measurements started as the sun was beginning to warm up the ice surface, reaching a peak, followed by a decline as the sun was setting. This data correlated well with the weather station data, despite the latter being located 1.7 m off the ground. The data logger naturally reported a slightly elevated relative humidity compared to the weather station. Despite that the dew point never exceeded temperature, hoar frost is formed, see Figure 4.4. As temperature is lower at the ice surface due to radiation. The last measurements on 2009-02-11 gave higher roadgrip due to hoar frost forming on the ice. Those results were removed from the data before analysis.

9 4.2. CONDITIONS DURING TESTS CHAPTER 4. METHODOLOGY

0 100 −2 90 −4 −6 80 −8 70

C) −10 ° −12 60 −14 50 −16 −18 40

Temperature ( −20 30

−22 Relative Humidity (%) −24 20 −26 10 −28 −30 0 10−Feb−2009 11−Feb−2009 12−Feb−2009

Figure 4.3: Temperature (blue line) and relative humidity (green line) together with dew point (red dotted line) in ◦C during test times (white areas) and night times (gray areas). Vertical dotted lines represent midnight.

Figure 4.4: Left: evidence of hoar frost growth during night. Right: a picture of ice crystals (hoar frost) as the sun settled.

Conditions from 2009-03-10 In March the average temperature had gone up, still safely below 0 ◦C. Because of plowing and brushing we had to place the USB data logger in the surrounding snow. This made relative humidity appear higher, still comparable to weather station data. Nighttime temperature in Figure 4.5 previous to the tests were stable. During daytime temperature goes up, but stays well below zero. However note that ice is more slippery at warmer temperatures[2].

10 4.3. DATA PRESENTATION CHAPTER 4. METHODOLOGY

0 100

−2 80

70 C) ° −4 60

−6 40 Temperature ( 30 Relative Humidity (%) −8 20

−10 0 10−Mar−2009

Figure 4.5: Temperature (blue line) and relative humidity (green line) together with dew point (red line) in ◦C during test times (white area) and nighttimes (gray areas).

4.3 Data presentation

Collected data is presented with graphs illustrating stop distances in [ m] and graphs illustrating m rate of deceleration in [ /s2 ]. In the graphs each vehicle is represented by a certain symbol. km km km Symbol size represents three speeds: 30 /h, 50 /h, and 70 /h. Every symbol represents one measurement. Each tire brand is color coded, for examples see Figure 5.1 or Figure D.1. The four shortest stop distances were extracted for each speed, surface type, tire, vehicle and day. As a precaution the shortest of those four were removed. Data is presented as an average minimum stop distance with two standard deviations for the different tire types to produce 95 % confidence intervals. In the graphs we also can see many measurements other than the four mentioned above. These measurements were recorded during preparations and not during steady state conditions. Each set of three stop distances is assembled in a table, see Appendix E were time, car type, “tire index”, speed, braking distance, temperature and relative humidity are listed for the different days and surface types.

11 Chapter 5

Results

Results will be presented according to the following list:

km km km • Tests from 30 /h and 50 /h to 0 /h, during March 10, 2009 on brushed old polished ice.

km km km • Tests from 30 /h and 50 /h to 0 /h, during February 11, 2009 on brushed old polished ice.

km km km • Tests from 30 /h and 50 /h to 0 /h, during February 12, 2009 on brushed old polished ice.

km km • Tests from 70 /h to 0 /h, during February 12, 2009 on brushed old polished ice.

km km km km • Tests from 30 /h, 50 /h and 70 /h to 0 /h, during February 11, 2009 on rough old system 2000 ice.

5.1 Brushed old polished ice, March 10, 2009

Stop distances for tires A2 and C2, were tested with a Volvo V70. Tests with used studded tires, F5 on a Ford Mondeo, were also performed to evaluate how they compare with new studless tires. See Figure 5.1 below. Temperatures during these tests were between -6 ◦C and -2.5 ◦C, see Figure 4.5 for condition data.

12 5.1. BRUSHED OLD POLISHED ICE, MARCH 10, 2009 CHAPTER 5. RESULTS

2009−03−10, braking distances on polished ice at 30km/h 100

80 1

70 0.8 60 A 0.6 C 50 F 0.4 V70 40 Ford 30 0.2 Braking distance [m]

20 0 1 2 3 10

0 A2 C2 F5 V70 Ford Mondeo

km Figure 5.1: Stop distances on brushed old polished ice at 30 /h, March 10, 2009. Bars represents average stop distances, horizontal lines represent two standard deviations

km Stop distances are similar in proportion at 30 /h (Figure 5.1), compared to results at km 50 /h (Figure 5.2). Old studded tires maintain their advantage over new studless tires. Vari- ations in breaking distance for studded winter tires are low. This is partially an artifact, as studless tires were used to clear the ice and stabilize conditions before tests with studded tires were performed. Studded tires had a lower total average. 2009−03−10, braking distances on polished ice at 50km/h 100

80 1

70 0.8 60 A 0.6 C 50 F 0.4 V70 40 Ford 30 0.2 Braking distance [m]

20 0 1 2 3 10

0 A2 C2 F5 V70 Ford Mondeo

km Figure 5.2: Stop distances on brushed old polished ice at 50 /h, March 10, 2009. Bars represents average stop distances, horizontal lines represent two standard deviations

Tire C2 was tested speciﬁcally as a magazine [7] claimed that this brand had horrible performance on ice. We found that the magazine [7] had a summer tire in their article and not a winter tire. This brand’s studless winter tire has no signiﬁcant weakness compared to tire A1 and tire C2 is better than average, in our tests.

13 5.2. BRUSHED OLD POLISHED ICE, FEBRUARY 11, 2009 CHAPTER 5. RESULTS

5.2 Brushed old polished ice, February 11, 2009

Figure 5.3 shows that tire A1 performs worse during February 11, 2009 compared with results during measurements made March 10, 2009, see Figure 5.1. Note that tires A1 and A2 are the same tires. The only difference of the testing equipment is what vehicle they were fitted on. This fact is interesting as ice temperature were higher during March 10, 2009. Generally ice is more slippery at that temperature [4]. However low temperatures affect roadgrip as rubber compound stiffens, especially if the rubber compound was made for a warmer climate. Temperatures during these tests were between -18 ◦C and -8 ◦C. For conditions during February 11, 2009 see Figure 4.3. There are several changes in test conditions that could have resulted in changed performance. It is however surprising that we lose performance, when a major factor suggested that we should have shorter stop distances during the brake tests made the February 11th. 2009−02−11, braking distances on polished ice at 30km/h 100

80 1

70 0.8 60 A 0.6 D 50 E C30 0.4 40 XC70 XC90 30 0.2 Braking distance [m]

20 0 1 2 3 10

0 A1 B1 D1 A3 B3 E3 A4 B4 D4 C30 XC70 XC90

km Figure 5.3: Stop distances on brushed old polished ice at 30 /h, February 11, 2009. Bars represents average stop distances, horizontal lines represent two standard deviations

Results in Figure 5.4 is interesting, as we can compare A brand tires on the Volvo C30 and the Volvo XC90. Loose particles on the ice resulted in longer preparation time to achieve stable conditions for tire A4, see Figure D.2 in Appendix D, when they were achieved, performance was km significantly better on polished ice than for any other tires we tested. Stop distance at 30 /h, for the Volvo C30 with A1 tires are 38 % longer, compared to stop distances measured for the km Volvo XC90 with A4 tires. See Appendix E. The difference at 50 /h was 48 %. These results are supported by Hjort [5] He found that the A4 tire was better than all but one of the new studded winter tire tested during his brake tests on ice at -3 ◦C. One can also read that the shore A value at 20 ◦C for tire A4 in Hjort´s test was 43. This shore value is significantly lower than any other tire tested. Second lowest in Hjort´s tests had a shore value of 55 and the highest value for a summer tire was 70. We were unable to find the Shore scale used, but assumed it to be A, as is typical for automobile tires. In We can also see what a huge impact debris has on the performance on smooth surfaces

14 5.3. BRUSHED OLD POLISHED ICE, FEBRUARY 12, 2009 CHAPTER 5. RESULTS

2009−02−11, braking distances on polished ice at 50km/h 100

80 1

70 0.8 60 A 0.6 D 50 E C30 0.4 40 XC70 XC90 30 0.2 Braking distance [m]

20 0 1 2 3 10

0 A1 B1 D1 A3 B3 E3 A4 B4 D4 C30 XC70 XC90

km Figure 5.4: Stop distances on brushed old polished ice at 50 /h, February 11, 2009. Bars represents average stop distances, horizontal lines represent two standard deviations

5.3 Brushed old polished ice, February 12, 2009

Figure 5.5 shows results of the same test that first was made the day before, February 11, 2009. Temperatures are comparable, see Figure 4.3. This data has a minimum spread. The difference between tire A1 and A4 has increased to 91 %, as is evident in Table E.3. The only real indication is that measurements for the XC90 with A4 tires from February 11, 2009, has two values close to each other and one significantly higher, see Table E.4. This indicates that the difference from the 11th actually underestimated roadgrip with the A4 tire. Otherwise the D type tires perform similar and comparable to the tires A1 on the C30. 2009−02−12, braking distances on polished ice at 30km/h 100

80 1

70 0.8 60 0.6 A 50 C C30 40 0.4 XC90 30 Braking distance [m] 0.2 20

0 10 1 2 3 0 A1 B1 D1 A3 B3 E3 A4 B4 D4 C30 XC70 XC90

km Figure 5.5: Stop distances on brushed old polished ice at 30 /h, February 12, 2009. Bars represents average stop distances, horizontal lines represent two standard deviations.

km km In Figure 5.6 the same pattern can be seen at 50 /h as for the results at 30 /h previously. A brand tires outperform the rest, and the B and D brand give comparable results, even if the

15 5.3. BRUSHED OLD POLISHED ICE, FEBRUARY 12, 2009 CHAPTER 5. RESULTS

B1 tires do outperform the D1. 2009−02−12, braking distances on polished ice at 50km/h 100

80 1

70 0.8 60 A 0.6 B 50 D 40 0.4 C30 XC90 30 Braking distance [m] 0.2 20

0 10 1 2 3 0 A1 B1 D1 A3 B3 E3 A4 B4 D4 C30 XC70 XC90

km Figure 5.6: Stop distances on brushed old polished ice at 50 /h, February 12, 2009. Bars represents average stop distances, horizontal lines represent two standard deviations.

km 70 /h tests were only made with A brand tires as seen in Figure 5.7, since other tires failed to stop in the 100 m brushed old polished ice area. Once again, A4 tires outperform the A1 tires. 2009−02−12, braking distances on polished ice at 70km/h 100 1

90 0.9

80 0.8

70 0.7

60 0.6 A 50 0.5 C30 40 XC90 0.4 30 Braking distance [m] 0.3 20 0.2 10 0.1 0 A1 B1 D1 0 A3 B3 E3 A4 B4 D4 C30 XC701 2 XC90 3

km Figure 5.7: Stop distances on brushed old polished ice at 70 /h, February 12, 2009. Bars represents average stop distances, horizontal lines represent two standard deviations.

5.3.1 Rough old system 2000 ice, February 11, 2009 Data from tests on rough old system 2000 ice were stable and contained small diﬀerences in stop distances, see Figure 5.8.

16 5.3. BRUSHED OLD POLISHED ICE, FEBRUARY 12, 2009 CHAPTER 5. RESULTS

2009−02−11, braking distances on rough ice at 30km/h 100

90 4 80 3.5 70 3 A 60 2.5 B C 50 2 E C30 40 1.5 XC70 30 1 XC90 Braking distance [m]

20 0.5

10 0 1 2 3 4 0 A1 B1 D1 A3 B3 E3 A4 B4 D4 C30 XC70 XC90

km Figure 5.8: Stop distances on brushed old system 2000 ice at 30 /h, February 11, 2009. Bars represents average stop distances, horizontal lines represent two standard deviations.

At higher speeds, see Figure 5.9, it is interesting to note that tire D4 outperforms tire A4, whereas both tire A1 and D1 on the Volvo C30 perform very similarly. The reason for the good performance with D4, are that harder rubber compounds results in stiﬀer thread pattern, this will create a strong physical connection through “gear interaction” with the rough ice surface and thus higher roadgrip. Think about this as how well the thread pattern resist bending. “Gear interaction” is the largest diﬀerence between friction and roadgrip. 2009−02−11, braking distances on rough ice at 50km/h 100

90 4 80 3.5 70 3 A 60 2.5 B C 50 2 E C30 40 1.5 XC70 30 1 XC90 Braking distance [m]

20 0.5

10 0 1 2 3 4 0 A1 B1 D1 A3 B3 E3 A4 B4 D4 C30 XC70 XC90

km Figure 5.9: Stop distances on rough old system 2000 ice at 50 /h, February 11, 2009. Bars represents average stop distances, horizontal lines represent two standard deviations.

Results are similar in Figure 5.10, D4 are slightly better than A4 on rough old system 2000 ice. The combined results for A4 on brushed old polished ice and on rough old system 2000 ice are much better then for tire D4, see Figure 5.6 for results on brushed old polished ice.

17 5.3. BRUSHED OLD POLISHED ICE, FEBRUARY 12, 2009 CHAPTER 5. RESULTS

2009−02−11, braking distances on rough ice at 70km/h 100

90 4 80 3.5 70 3 A 60 2.5 B C 50 2 E C30 40 1.5 XC70 30 1 XC90 Braking distance [m]

20 0.5

10 0 1 2 3 4 0 A1 B1 D1 A3 B3 E3 A4 B4 D4 C30 XC70 XC90

km Figure 5.10: Stop distances on rough old system 2000 ice at 70 /h, February 11, 2009. Bars represents average stop distances, horizontal lines represent two standard deviations.

18 Chapter 6

Discussion

Testing a large amount of tires on different vehicles requires planning down to the smallest details, significant material resources and trained personnel. We are well on our way to collect experience to successfully perform winter tire tests in a professional manner. In the magazine Auto Motor & Sport [7] a summer tire (Goodride R-VH680) was tested and the brand Goodride was discredited. The magazine wrote that it was a dangerous winter tire that should not be allowed to be sold in Sweden. Goodride R-VH680 is not a winter tire, it is a summer tire. Tire C2 (Goodride SW601) is not dangerous at all. Further more, tire C2 are not on the list of approved winter tires and we had to get it from Europe. Goodride does not have any tire on the list of approved winter tires. We see no reason why their model SW601 should not be approved for winter use. Tire A4 significantly outperforms all other tires on brushed old polished ice, including other tires from the same brand. It is important to note that the high grip SUV tires A3 and A4, fitted on the Volvo XC70 and XC90, were manufactured in Japan. The rubber compound in tires A3 and A4 is softer [5] than rubber compounds in the European manufactured A1 and A2 tires. Our theory is that the soft rubber compound is the key to this high roadgrip on brushed old polished ice. The reason for the softer rubber compound are regulations in Japan that forbids studded winter tires. This drives the need to adapt the rubber compound such that it produce high roadgrip on dangerous surfaces. This is a clear indication that research should be made on different rubber compounds and on their characteristics. This will result in better winter tires and correct information to owners of vehicles such that they can purchase the right type of winter tires for their use. One objective was to measure if there was a difference in stop distance depending on the size or weight of the vehicle. We found no roadgrip differences originating from size and weight. During our measurements effects originating from the tires dominates the length of the stop distances, not the size or weight. Tires are manufactured specifically for different types of vehicles and are so different that no direct comparison is possible. No tire made for a small car should be used on a big, high SUV, as this type of vehicle is prone to rollover in many types of accidents. Roadgrip on rough old system 2000 ice was good and even during these tests with new studless winter tires. During brake tests made March 19, 2008, see technical report “Road grip test in Arjeplog” [3] it was found that used tires can have large differences in roadgrip on rough old system 2000 ice. Rough old system 2000 ice is a surface that together with good winter tires create relatively good roadgrip. The situation is not the same if the vehicle has bad winter tires. Rubber compounds made for warmer temperatures gets very glassy and stiff in low temperatures, this reduces the roadgrip and unless the wavelength of the asperities in the road surface are close

19 CHAPTER 6. DISCUSSION to the tread pattern and will result in low levels of roadgrip. Another important finding was how significantly roadgrip was affected by a low amount of lose snow and/or ice particles on the ice surface. Some of the tested tires collected snow on the thread pattern, and in the cold environment, snow to ice friction is quite low [2]. If the layer was thin enough and not all over the thread pattern, it seemed like snow crystals could act as “glue” between the tire and the ice surface and thus increase the roadgrip. Hoar frost, forming on the ice surface as the sun settled (Figure 4.4), also severely disturbed the measurements. Braking on a brushed old polished ice surface with freshly regenerated ice crystals increased the roadgrip compared with brake test in tracks that had been freshly polished by earlier brake tests. More research will be done to address the importance of rubber compound in these and other tires. Tire A4 was about average on rough ice see Figure 5.10. The advantage that the soft rubber had on smooth ice surfaces are gone, as the “gear interaction” forces are reduced compared to tires with harder rubber compound. According to Figure 5.1 and Figure 5.2 Old Studded winter tires outperforms new studless winter tires with 9% - 11% on brushed old polished ice. Measurements verify that studded tires maintain safe levels of roadgrip on hard ice surfaces as the tire age and wear.

20 Chapter 7

Conclusions

Results show large performance diﬀerences between the tested tires, some with long stop distances and others with very short stop distance, like the A4 tire with surprisingly short stop distances, see Figure 5.4. This leads to the conclusion that there should be a classiﬁcation system for winter tires. Our recommendation for classes are: • Nordic winter tire • European winter tire

• South European winter tire Results from tests on rough system 2000 ice show low differences between all tires and high roadgrip. This in combination with the fact that there are less grip related accidents on surfaces with high grip, indicate that classifications should be performed on one or more low grip surfaces, such as brushed old polished ice. Another important road condition to consider is "black ice", which is asphalt covered with a thin sheet of clear ice. This condition is very difficult to visually detect for a driver and is therefor a threat to safe transportation. To ensure adequate traffic safety, road grip has to be measured [3]. The best way to measure roadgrip is by using real winter tires. The fundamental reason for this is that the rubber compound are similar to almost all winter tires used. A winter tire index for critical surfaces and/or winter tire classifications are needed to help vehicle owner when they select appropriate winter tires. Today it is close to impossible to de- termine what different winter tires are good at. This should be based on measurements with a standard roadgrip measurement unit and one or several standardized winter tire tests. Stan- dardized tests should be performed under well controlled conditions. If one use full scale tests with a car, then we recommend an enclosed building with climate control. Getting comparable results from different field tests is difficult since conditions are unstable. No relation between stop distance and vehicle weight could be found. Tire model is the most dominant factor when it comes to roadgrip. Further investigations of rubber compounds is important to increase understanding of roadgrip.

21 Bibliography

[1] S. R. Administration, “Vägverkets författningssamling 2003:22 kap. 9 §3,” www.vv.se, N/A 2003, address for hard copy Vägverket, 781 87 Borlänge. By E-mail, [email protected]. [2] G. Casassa, H. Narita, and N. Maeno, “Shear cell experiments of snow and ice friction,” Journal of Applied Physics, vol. 69, no. 6, pp. 3745–3756, March 1991.

[3] N. Engström, H. Andrén, R. Larsson, L. Fransson, and M. Nybacka, “Road grip test in Arjeplog,” Luleå University of Technology, Luleå University of Technology, 97187 Luleå, Technical report ISSN:1402-1536, 2008, test with several roadgrip measuring devices. [4] I. Golecki and C. Jaccard, “Intrinsic surface disorder in ice near the melting point,” Journal of Physics C, vol. 11, pp. 4229–4237, May 1978. [5] M. Hjort, “SUV-däcks väggrepp på is,” Statens Väg- och transportforskningsinstitut, VTI, VTI, 581 95 Linköping, Technical report 58-2005, December 2006, blizzak DM-Z3 is in the report. [6] D. Informationsråd, “Undersökning av däcktyp samt mönsterdjup i Sverige,” Däckbranschens Informationsråd, Slottsgatan 8, 432 44 Varberg, Publikation 2009:41, Januari/februari 2009, beställd av Vägverket, kontaktperson Pontus Grönvall, Tel: 0340-673001. [7] M. Ström, “Ta kontroll,” Auto motor & sport, no. 21, pp. 52–60, oktober 2008, test of 21 studless and studded winter tires.

22 List of Figures

1.1 Test track Layout during stop distance measurements on Brushed old Polished Ice. 3

4.1 Test track Layout during brake tests on brushed old polished Ice. Driving direction is from right to left...... 8 4.2 Clear smooth polished ice made over rough system 2000 ice...... 8 4.3 Temperatures and humidities on 2009-02-09 to 2009-02-13...... 10 4.4 Ice crystallizations on objects and test surface...... 10 4.5 Temperatures and humidities on 2009-03-10...... 11

km 5.1 Stop distances on brushed old polished ice at 30 /h...... 13 km 5.2 Stop distances on brushed old polished ice at 50 /h...... 13 km 5.3 Stop distances on brushed old polished ice at 30 /h...... 14 km 5.4 Stop distances on brushed old polished ice at 50 /h...... 15 km 5.5 Stop distances on brushed old polished ice at 30 /h...... 15 km 5.6 Stop distances on brushed old polished ice at 50 /h...... 16 km 5.7 Stop distance on brushed old polished ice at 70 /h...... 16 km 5.8 Stop distances on rough old system 2000 ice at 30 /h...... 17 km 5.9 Stop distances on rough old system 2000 ice at 50 /h...... 17 km 5.10 Stop distances on rough old system 2000 ice at 70 /h...... 18

B.1 Test cars XC90, XC70 and C30 ...... 28 B.2 Test cars V70 and Mondeo ...... 29

C.1 V-Box3 ...... 30 C.2 Certiﬁcate for V-Box3i ...... 32 C.3 Certiﬁcate for IMU02 ...... 33

D.1 Braking tests on brushed old polished ice on 2009-03-10...... 34 D.2 Braking tests on brushed old polished ice on 2009-02-11...... 35 D.3 Braking tests on brushed old polished ice on 2009-02-12...... 35 D.4 Braking tests on rough old system 2000 ice on 2009-02-11...... 36

F.1 Deceleration curve at 100 Hz ...... 43

23 List of Tables

B.1 Test cars XC90, XC70 and C30 ...... 28 B.2 Test cars V70 and Mondeo ...... 29

C.1 VB3i Speciﬁcation ...... 31

E.1 Shortest braking distances 2009-03-10 on polished ice...... 37 E.2 Shortest braking distances 2009-02-11 on polished ice...... 38 E.3 Shortest braking distances 2009-02-12 on polished ice...... 39 E.4 Shortest braking distances 2009-02-11 on rough ice...... 40

24 Appendix A

Tires

Label A1/A2 B1 D1 C2 Brand Bridgestone Continental GT GoodRide Blizzak Nordic SW601 Model Viking Contact 5 Champiro WT-AX WN-01 (Snowmaster)

Tire side

Thread

Size 205/55 R16 205/55 R16 205/55 R16 205/55 R16 Manufacture 11-2008 44-2008 21-2008 43-2008 date Mounting Rotation Outside Outside Outside instruction Type WTSLR WTSLR WTSLR WTSLR Country of Europe Germany Indonesia China origin Load rating 94R 94T 94H 91H Thread depth 8.7 mm 8.2 mm 8.6 mm 7.5 mm Veriﬁed on yes yes yes Not on list1 STRO list

1These tires were imported from Europe as they not are on the STRO-list of approved winter tires.

25 Label A3 B3 E3 Brand Bridgestone Continental Wanli 4x4 Cross Contact Model Blizzak DM-Z3 Snowgrip Winter

Tire side

Thread

Size 215/65 R16 215/65 R16 215/65 R16 Manufacture 29-2008 10-2008 34-2007 date Mounting Rotation Outside Rotation instruction Type WTSLR WTSLR WTSLR Country of Japan Germany China origin Load rating 98Q 98T 98H Thread depth 10.3 mm 8.5 mm 7.7 mm2 Veriﬁed on yes yes yes STRO list

28.1 mm in central furrow.

26 Label A4 B4 D4 Brand Bridgestone Continental GT Viking 4x4 Model Blizzak DM-Z3 Savero WT WinterContact

Tire side

Thread

Size 235/65 R17 235/65 R17 235/65 R17 Manufacture 26-2008 28-2008 26-2008 date Mounting Rotation Outside Rotation instruction Type WTSLR WTSLR WTSLR Country of Japan Czech Republic China origin Load rating 108Q 104H 104T Thread depth 10.0 mm 8.6 mm 10.9 mm Veriﬁed on yes yes yes STRO list

27 Appendix B

Vehicles

B.1 Vehicles 2009-02-09–2009-02-13

Table B.1: Test cars XC90, XC70 and C30 Make & Model Volvo C30 Volvo XC70 Volvo XC90 Reg no. EBS 546 HDW 880 JME 793 Color Light blue Light gray Gray Year 2007 2008 2008 Chassi no. YV1MK084- YV1BZ714- YV1CZ714- 282066130 691050380 691499405 Type Sedan Sedan Sedan Transmission Manual Automatic Automatic Service weight 1330 kg 1820 kg 2150 kg Total weight 1750 kg 2400 kg 2750 kg Tire dim. 205/55 R16 91V 215/65R16 102V 235/65 R17 104V Rim dim. 6,5JX16X52,5 7JX16X50 Length 4250 mm 4950 mm 4800 mm Width 1790 mm 1890 mm 1910 mm Height 1450 mm 1610 mm 1790 mm

Figure B.1: Test cars XC90, XC70 and C30

28 B.2 Vehicles 2009-03-09–2009-03-10

Table B.2: Test cars V70 and Mondeo Make & model Volvo V70 Ford Mondeo Reg no. DPS 040 GLC 058 Color Red Gray Year 2008 2007 Chassi no. YV1BW694- WF0GXXGB- 191077362 BG7U29312 Type Sedan Sedan Transmission Manual Manual Service weight 1680 kg 1580 kg Total weight 2300 kg 2280 kg Tire dim. 205/60 R16 96V 215/55 R16 90V Rim dim. 7JX16X50 6.5JX16H2OS50.0 Length 4960 mm 4850 mm Width 1890 mm 1890 mm Height 1550 mm 1470 mm

Figure B.2: Test cars V70 and Mondeo

29 Appendix C

V-Box3i

Stop distance measurements were carried out with LTU:s V-Box3i and a V-Box3 from Artic falls. Both were equiped with inertial motion sensors, IMU02.

Figure C.1: V-Box3

30 C.1 Speciﬁcation

Table C.1: VB3i Speciﬁcation Make & Model RACELOGIC VB3i Distance Accuracy 0.05 % Update rate 100 Hz Resolution 1 cm Height resolution 6 m Velocity Km Accuracy 0.1 /h Update rate 100 Hz Maximum velocity 1000 Mph Km Minimum velocity 0.1 /h Km Resolution 0.01 /h Latency 6.75 ms Absolute Positioning Accuracy 3 m 95 % CEP Update rate 100 Hz Resolution 1.8 mm Heading Resolution 0.01 ◦ Accuracy 0.1 ◦ Acceleration Accuracy 0.5 % Maximum 20 g Resolution 0.01 g Update rate 100 Hz

31 C.2 Certiﬁcates

Figure C.2: Certiﬁcate for V-Box3i

32 Figure C.3: Certiﬁcate for IMU02

33 Appendix D

Deceleration

To compare diﬀerent initial speeds and calculate roadgrip values, see Appendix F and Figure F.1, deceleration values are presented in addition to stop distance. Data is presented as averaged 100 Hz samplings of deceleration during the entire braking sequence. This is discussed further in Appendix F.

D.1 Brushed old polished ice, March 10

Data in Figure D.1 reveals that the studded tires F5 on the Ford Mondeo had better grip on brushed old polished ice than studless tires tested that day. At the end of the day deceleration was greater for the A2 tire then for tire C2. It had been very close during the two earlier test sessions.

] 3.5 2 3 V70 C2 30km/h 2.5 V70 C2 50km/h 2 Mondeo F5 30km/h Mondeo F5 50km/h 1.5 V70 A2 30km/h 1 V70 A2 50 km/h

Deceleration [m/s 0.5

09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 Time of day [h]

Figure D.1: Braking tests with studless tires A2 and C2 ﬁtted on a Volvo V70 and studded tires F5 ﬁtted on a Ford Mondeo during March 10, 2009 on brushed old polished ice with an average temperature of -6 ◦C.

Temperature was stable during the entire day, snow was drifting onto the track especially in the beginning of the day. We had to brush the ice surface and drive over the ice surface to remove debris, these actions resulted in stabilized measurements.

34 D.2 Brushed old polished ice, Februrary 11-12

It can be seen in Figure D.2 and Figure D.3 that tires A1 and A4 outperforms other tires on most runs. Tires B1 and B4 performs similarly to D1 and D4.

] 3.5 C30 D1 50km/h 2 3 C30 D1 30km/h XC70 E3 50km/h 2.5 XC70 E3 30km/h 2 XC90 D4 50km/h 1.5 C30 A1 50km/h C30 A1 30 km/h 1 XC90 A4 50 km/h Deceleration [m/s 0.5 XC90 A4 30 km/h

09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 Time of day [h]

Figure D.2: Decelerations on brushed old polished ice during February 11, 2009 for tires A1, D1, A3, E3, A4 and D4 with Volvo C30, Volvo XC70 and Volvo XC90.

4 C30 D1 50km/h C30 D1 30km/h

] 3.5 2 XC90 D4 50km/h 3 XC90 D4 30km/h 2.5 C30 B1 50km/h 2 XC90 B4 50km/h C30 A1 70 km/h 1.5 C30 A1 50 km/h 1 C30 A1 30 km/h

Deceleration [m/s XC90 A4 70 km/h 0.5 XC90 A4 50 km/h XC90 A4 30 km/h 09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 Time of day [h]

Figure D.3: Decelerations on brushed old polished ice during February 12, 2009 for tires A1, D1, A3, E3, A4 and D4 with Volvo C30, Volvo XC70 and Volvo XC90.

D.3 Rough old system 2000 ice, February 11

This is probably the least interesting surface, since most tires break very well and roadgrip is good. Interesting to note in Figure D.4 is that tires A4 performs in the lower parts of the spectrum, not signiﬁcantly worse than any other tire.

35 4 C30 D1 70km/h C30 D1 50km/h

] 3.5 C30 D1 30km/h 2 3 XC70 E3 70km/h XC70 E3 50km/h 2.5 XC70 E3 30km/h 2 XC90 D4 70km/h XC90 D4 50km/h 1.5 C30 A1 70km/h 1 C30 A1 50km/h C30 A1 30 km/h Deceleration [m/s 0.5 XC90 A4 70 km/h XC90 A4 50 km/h

09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 XC90 A4 30 km/h Time of day [h]

Figure D.4: Decelerations on rough old system 2000 ice February 11, 2009 for tires A1, D1, A3, E3, A4 and D4 with Volvo C30, Volvo XC70 and Volvo XC90.

36 Appendix E

Shortest stop distances

In tables Table E.2 to Table E.1 the measurements are listed according to date, ice type, car, tire and speed. Only the second shortest to fourth shortest stop distance are represented1 this as we found that very short stop distances could occur when hoar frost increased roadgrip. Many of the longer stop distances measured were due to snow and other lose particles on the track.

E.1 Brushed old polished ice during March 10, 2009

Table E.1: Shortest braking distances 2009-03-10 on polished ice. Average of a set of measurements are given together with one standard deviation, all in meters.

Time Vehicle Tire Speed Dist. Dec. Temp. Relative km m ◦ HH:MM:SS type index ( /h)( m)( /s2 )( C) humidity 09:41:08 V70 2C 30 21.76 -1.59 -6.00 86.50% 09:39:32 V70 2C 30 21.94 -1.61 -6.00 86.50% 09:36:23 V70 2C 30 22.99 -1.58 -6.00 86.50% Average braking distance: 22.23 Standard deviation: 0.66 09:32:00 V70 2C 50 55.72 -1.71 -6.00 86.50% 09:28:58 V70 2C 50 56.35 -1.71 -6.00 86.50% 09:26:02 V70 2C 50 57.09 -1.65 -6.00 86.50% Average braking distance: 56.39 Standard deviation: 0.69 13:29:38 V70 2A 30 22.45 -1.53 -4.50 87.50% 16:33:41 V70 2A 30 22.47 -1.55 -6.00 86.50% 13:26:34 V70 2A 30 22.67 -1.51 -4.50 87.50% Average braking distance: 22.53 Standard deviation: 0.12 10:34:15 V70 2A 50 57.11 -1.66 -3.00 89.50% 16:35:01 V70 2A 50 57.23 -1.63 -6.00 86.50% 09:59:19 V70 2A 50 57.52 -1.65 -5.00 88.00% Average braking distance: 57.29 Standard deviation: 0.21 Time Vehicle Tire Speed Dist. Dec. Temp. Relative km m ◦ HH:MM:SS type index ( /h)( m)( /s2 )( C) humidity

1If a fourth stop distance not are available, then only two measurements are presented

37 Time Vehicle Tire Speed Dist. Dec. Temp. Relative km m ◦ HH:MM:SS type index ( /h)( m)( /s2 )( C) humidity 14:52:11 Ford 5F 30 18.49 -1.87 -4.00 87.50% 14:56:14 Ford 5F 30 18.54 -1.85 -4.00 87.50% 14:54:30 Ford 5F 30 18.77 -1.82 -4.00 87.50% Average braking distance: 18.60 Standard deviation: 0.15 14:59:39 Ford 5F 50 50.09 -1.93 -4.00 87.50% 15:03:00 Ford 5F 50 50.37 -1.92 -4.00 88.00% 14:36:58 Ford 5F 50 50.54 -1.88 -3.50 88.00% Average braking distance: 50.33 Standard deviation: 0.23 Time Vehicle Tire Speed Dist. Dec. Temp. Relative km m ◦ HH:MM:SS type index ( /h)( m)( /s2 )( C) humidity

E.2 Brushed old polished ice during February 11, 2009

Table E.2: Shortest braking distances 2009-02-11 on polished ice. Average of a set of measurements are given together with one standard deviation, all in meters.

Time Vehicle Tire Speed Dist. Dec. Temp. Relative km m ◦ HH:MM:SS type index ( /h)( m)( /s2 )( C) humidity 15:28:15 C30 1A 30 25.21 -1.39 -11.50 61.50% 15:23:07 C30 1A 30 26.78 -1.30 -11.00 61.50% Average braking distance: 26.00 Standard deviation: 1.11 16:53:21 C30 1D 30 29.27 -1.21 -10.00 72.50% 16:50:17 C30 1D 30 30.60 -1.18 -10.00 72.50% Average braking distance: 29.94 Standard deviation: 0.94 11:12:47 XC70 3D 30 26.67 -1.26 -12.00 66.50% 11:10:41 XC70 3D 30 28.28 -1.24 -12.00 66.50% Average braking distance: 27.48 Standard deviation: 1.14 15:40:13 XC90 4A 30 15.26 -2.38 -11.50 65.00% 15:45:11 XC90 4A 30 16.55 -2.23 -11.50 67.00% 15:35:26 XC90 4A 30 24.85 -1.71 -12.00 63.00% Average braking distance: 18.89 Standard deviation: 5.20 15:32:28 C30 1A 50 47.26 -1.78 -11.50 61.50% 15:30:57 C30 1A 50 56.20 -1.66 -11.50 61.50% Average braking distance: 51.73 Standard deviation: 6.32 16:32:19 C30 1D 50 76.12 -1.29 -10.50 72.50% 16:37:08 C30 1D 50 76.95 -1.26 -10.50 72.00% 16:35:01 C30 1D 50 78.19 -1.24 -10.50 72.50% Average braking distance: 77.09 Standard deviation: 1.04 11:08:26 XC70 3D 50 71.61 -1.36 -12.50 66.50% 11:04:23 XC70 3D 50 72.19 -1.36 -12.50 66.50% Average braking distance: 71.90 Standard deviation: 0.41 Time Vehicle Tire Speed Dist. Dec. Temp. Relative km m ◦ HH:MM:SS type index ( /h)( m)( /s2 )( C) humidity

38 Time Vehicle Tire Speed Dist. Dec. Temp. Relative km m ◦ HH:MM:SS type index ( /h)( m)( /s2 )( C) humidity 15:29:45 XC90 4A 50 34.41 -2.85 -11.50 61.50% 15:31:09 XC90 4A 50 34.44 -2.83 -11.50 61.50% 15:27:16 XC90 4A 50 36.29 -2.68 -11.50 61.00% Average braking distance: 35.05 Standard deviation: 1.08 10:36:59 XC90 4D 50 89.00 -1.18 -13.50 63.50% 10:42:55 XC90 4D 50 89.62 -1.10 -13.50 64.00% Average braking distance: 89.31 Standard deviation: 0.44 Time Vehicle Tire Speed Dist. Dec. Temp. Relative km m ◦ HH:MM:SS type index ( /h)( m)( /s2 )( C) humidity

E.3 Brushed old polished ice during February 12, 2009

Table E.3: Shortest braking distances 2009-02-12 on polished ice. Average of a set of measurements are given together with one standard deviation, all in meters.

Time Vehicle Tire Speed Dist. Dec. Temp. Relative km m ◦ HH:MM:SS type index ( /h)( m)( /s2 )( C) humidity 11:41:44 C30 1A 30 21.56 -1.70 -12.00 51.50% 11:31:04 C30 1A 30 22.83 -1.67 -11.00 55.50% 11:29:15 C30 1A 30 22.84 -1.66 -11.00 56.50% Average braking distance: 22.41 Standard deviation: 0.74 14:56:36 C30 1D 30 24.48 -1.50 -11.50 62.00% 14:55:15 C30 1D 30 25.23 -1.42 -11.50 62.50% 09:26:31 C30 1D 30 25.29 -1.49 -13.00 60.50% Average braking distance: 25.00 Standard deviation: 0.45 11:44:40 XC90 4A 30 11.55 -3.11 -12.50 51.00% 11:39:26 XC90 4A 30 11.79 -3.08 -11.50 52.00% 11:42:54 XC90 4A 30 11.91 -3.08 -12.00 51.00% Average braking distance: 11.75 Standard deviation: 0.18 14:59:54 XC90 4D 30 23.63 -1.59 -11.50 62.00% 14:56:16 XC90 4D 30 23.65 -1.52 -11.50 62.50% 14:47:18 XC90 4D 30 23.67 -1.56 -12.00 60.50% Average braking distance: 23.65 Standard deviation: 0.02 11:54:16 C30 1A 50 40.82 -2.47 -13.00 55.50% 11:47:34 C30 1A 50 41.43 -2.45 -13.00 51.50% 11:49:43 C30 1A 50 41.70 -2.43 -13.00 53.00% Average braking distance: 41.32 Standard deviation: 0.45 16:32:45 C30 1B 50 48.37 -2.13 -14.50 50.00% 16:39:52 C30 1B 50 52.26 -1.99 -14.50 51.00% 16:56:37 C30 1B 50 54.24 -1.92 -15.00 53.50% Average braking distance: 51.62 Standard deviation: 2.99 Time Vehicle Tire Speed Dist. Dec. Temp. Relative km m ◦ HH:MM:SS type index ( /h)( m)( /s2 )( C) humidity

39 Time Vehicle Tire Speed Dist. Dec. Temp. Relative km m ◦ HH:MM:SS type index ( /h)( m)( /s2 )( C) humidity 09:42:35 C30 1D 50 69.07 -1.40 -13.00 61.50% 09:38:38 C30 1D 50 69.33 -1.43 -13.00 62.00% 09:40:48 C30 1D 50 71.12 -1.40 -13.00 62.00% Average braking distance: 69.84 Standard deviation: 1.12 11:35:18 XC90 4A 50 31.85 -3.13 -11.50 55.50% 11:32:11 XC90 4A 50 32.12 -3.08 -11.50 54.50% 11:25:10 XC90 4A 50 32.50 -3.09 -11.50 58.50% Average braking distance: 32.16 Standard deviation: 0.33 16:31:02 XC90 4B 50 55.01 -1.87 -14.50 50.50% 16:28:09 XC90 4B 50 55.59 -1.83 -14.00 52.00% 16:36:35 XC90 4B 50 55.97 -1.84 -14.50 52.50% Average braking distance: 55.52 Standard deviation: 0.48 09:23:50 XC90 4D 50 57.91 -1.74 -13.00 60.50% 14:37:04 XC90 4D 50 59.49 -1.73 -12.00 57.50% 14:35:25 XC90 4D 50 60.29 -1.68 -12.00 57.50% Average braking distance: 59.23 Standard deviation: 1.21 12:02:05 C30 1A 70 74.38 -2.59 -12.00 57.00% 11:58:40 C30 1A 70 76.22 -2.50 -12.50 56.50% 12:00:23 C30 1A 70 76.79 -2.56 -12.50 57.00% Average braking distance: 75.80 Standard deviation: 1.26 11:47:56 XC90 4A 70 52.46 -3.70 -13.00 51.50% 11:46:28 XC90 4A 70 55.01 -3.58 -12.50 51.00% Average braking distance: 53.73 Standard deviation: 1.80 Time Vehicle Tire Speed Dist. Dec. Temp. Relative km m ◦ HH:MM:SS type index ( /h)( m)( /s2 )( C) humidity

E.4 Rough old system 2000 ice during February 11, 2009

Table E.4: Shortest braking distances 2009-02-11 on rough ice. Av- erage of a set of measurements are given together with one standard deviation, all in meters.

Time Vehicle Tire Speed Dist. Dec. Temp. Relative km m ◦ HH:MM:SS type index ( /h)( m)( /s2 )( C) humidity 15:12:57 C30 1A 30 11.14 -3.12 -10.50 65.50% 15:12:00 C30 1A 30 11.45 -2.96 -10.50 65.00% Average braking distance: 11.30 Standard deviation: 0.22 16:49:17 C30 1D 30 12.26 -2.78 -10.00 72.50% 16:47:44 C30 1D 30 12.76 -2.73 -10.00 72.50% Average braking distance: 12.51 Standard deviation: 0.35 Time Vehicle Tire Speed Dist. Dec. Temp. Relative km m ◦ HH:MM:SS type index ( /h)( m)( /s2 )( C) humidity

40 Time Vehicle Tire Speed Dist. Dec. Temp. Relative km m ◦ HH:MM:SS type index ( /h)( m)( /s2 )( C) humidity 11:14:08 XC70 3D 30 12.20 -2.82 -12.00 66.50% 11:09:46 XC70 3D 30 13.07 -2.59 -12.00 66.50% Average braking distance: 12.64 Standard deviation: 0.62 15:32:39 XC90 4A 30 11.65 -2.91 -11.50 61.50% 15:34:38 XC90 4A 30 13.04 -2.62 -12.00 63.00% Average braking distance: 12.34 Standard deviation: 0.98 15:14:46 C30 1A 50 31.29 -3.16 -10.50 65.00% 15:13:55 C30 1A 50 34.01 -3.01 -10.50 65.00% Average braking distance: 32.65 Standard deviation: 1.92 16:28:27 C30 1D 50 32.96 -2.91 -10.50 72.00% 16:27:21 C30 1D 50 34.04 -2.80 -10.50 72.00% Average braking distance: 33.50 Standard deviation: 0.76 11:07:39 XC70 3D 50 35.84 -2.59 -12.50 66.50% 11:05:37 XC70 3D 50 36.59 -2.56 -12.50 66.50% Average braking distance: 36.22 Standard deviation: 0.53 15:03:30 XC90 4A 50 33.53 -2.88 -10.00 65.50% 15:01:12 XC90 4A 50 34.28 -2.85 -10.00 66.00% Average braking distance: 33.91 Standard deviation: 0.53 10:41:52 XC90 4D 50 28.38 -3.32 -13.50 63.50% 10:39:32 XC90 4D 50 29.04 -3.23 -13.50 63.50% Average braking distance: 28.71 Standard deviation: 0.47 15:09:10 C30 1A 70 58.78 -3.24 -10.50 64.50% 15:07:27 C30 1A 70 62.51 -3.00 -10.50 65.00% Average braking distance: 60.64 Standard deviation: 2.64 16:41:48 C30 1D 70 64.86 -2.97 -10.00 72.50% 16:46:34 C30 1D 70 68.74 -2.69 -10.00 72.50% Average braking distance: 66.80 Standard deviation: 2.74 11:19:25 XC70 3D 70 65.57 -3.00 -12.00 67.00% 11:17:39 XC70 3D 70 70.18 -2.69 -12.00 66.50% Average braking distance: 67.88 Standard deviation: 3.26 14:51:08 XC90 4A 70 63.71 -2.85 -9.50 68.50% 14:53:27 XC90 4A 70 65.74 -2.80 -9.50 67.50% Average braking distance: 64.72 Standard deviation: 1.44 Time Vehicle Tire Speed Dist. Dec. Temp. Relative km m ◦ HH:MM:SS type index ( /h)( m)( /s2 )( C) humidity

41 Appendix F

Theory

F.1 Basic kinetics

According to physics, force, mass and acceleration are related according to the equation below, X F = ma (F.1)

P m F is the sum of forces in Newtons, m is the mass in kg and a is the acceleration in /s2 . The major acting force in deceleration is the friction/roadgrip between tires and road. Described as

Fµ = µN = µgm (F.2) µ is the friction coeﬃcient and N is the normal force, i.e. the weight of the car expressed in m Newtons or mg, where g is the acceleration due to gravity, commonly 9.82 /s2 . Since m appears in both equations we can put a ma = µN = µgm ⇒ µ = . (F.3) g Giving us a direct relation between deceleration and friction coeﬃcient. Since for constant deceleration1

|v | t = 0 (F.4) s |a|

v = v0 + ats (F.5) Z t 2 2 at |v0| |v0| s = v(ts)dt = v0ts + = v0 + a 2 (F.6) 0 2 |a| |a |2 v |v | a|v |2 2v |v ||a| + a|v |2 2v |v ||a| + av2 s = 0 0 + 0 = 0 0 0 = 0 0 0 (F.7) |a| 2|a|2 2|a|2 2a2 since a is negative and v0 is positive when it comes to braking 2(−a)v2 + av2 av2 − 2av2 −av2 −v2 v2 s = 0 0 = 0 0 = 0 = 0 ≈ 0 . (F.8) 2a2 2a2 2a2 2a 20µ

1A reasonable assumption since roadgrip and friction coeﬃcient should be stable on this specially prepared surface.

42 m Stop distance s in meters is dependent on the square of the initial speed v0 in /s and linear m to deceleration a in /s2 . Time t are in seconds.

F.2 Deceleration measurements

Deceleration is speed dependent, due to eﬀects from the cars ABS system and frequency related properties in the rubber compounds. Deceleration of braking from 50 km/h to 0. 0.2 50 45 0.1

40 0 ] 35 2 −0.1 30 25 −0.2

Speed [km/h] 20 −0.3 Deceleration [m/s 15 −0.4 10 −0.5 5 −0.6 0 1 2 3 4 5 Time [s]

Figure F.1: Deceleration and speed measured with a VBox3i during full ABS-braking from km km 50 /h to 0 /h. Brake point and stop point is marked with vertical red lines. Calculated average deceleration is marked with a diagonal red line, a small time/position dependence between speed and average deceleration can be seen.

Figure F.1 illustrate unprocessed deceleration values, picking up vibrations transmitted through the car from the test surface. Calculated average deceleration is compared to speed and we see that deceleration is very stable, indicating that surface characteristics are stable throughout the brake test area during this test. v a = − 0 , (F.9) ts In Equation F.9 a is the average deceleration during the stop distance measurement, d is braking distance in m and t is the time in s it takes from initiation of brakes to full stop. This equation is used to calculate a deceleration value, we use a to compare results from VBox units to see if the test is valid. If there are large deviations during the test run something went wrong.