TECHNICAL REPORT
Stop distances
for ten studless winter tires
Niclas Engström Henrik Andrén Roland Larsson Lennart Fransson
ISSN: 1402-1536 ISBN 978-91-7439-041-4 Luleå University of Technology 2009
Division of Machine Elements Division of Structural Engineering,
October 9, 2009, rev 0.9
Stop distances
for ten studless winter tires
Niclas Engström
aHenrik Andrén
bRoland Larsson
aand Lennart Fransson
ba
Division of Machine Elements, Luleå University of Technology
b
Division of Structural Engineering, Luleå University of Technology
Supported by:
Kempe foundations, I2, CASTT and the Swedish Road Administration.
Academic partners:
October 9, 2009, rev 0.9
Stop distances
for ten studless winter tires
Niclas Engström
aHenrik Andrén
bRoland Larsson
aand Lennart Fransson
ba
Division of Machine Elements, Luleå University of Technology
b
Division of Structural Engineering, Luleå University of Technology
Supported by:
Kempe foundations, I2, CASTT and the Swedish Road Administration.
Academic partners:
October 9, 2009, rev 0.9
Stop distances
for ten studless winter tires
Niclas Engström
aHenrik Andrén
bRoland Larsson
aand Lennart Fransson
ba
Division of Machine Elements, Luleå University of Technology
b
Division of Structural Engineering, Luleå University of Technology
Supported by:
Kempe foundations, I2, CASTT and the Swedish Road Administration.
Academic partners:
ISSN: 1402-1536
ISBN 978-91-7439-041-4
Luleå 2009
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
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
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 Brushed old polished ice
100 m
Brake activation
marker
M
5 m
Vehicle tire paths
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.
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.
Speeds of 30
km/
h, 50
km/
hand some times 70
km/
hwere used during the stop distance mea- surements.
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.
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 T
g, 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.
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.
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 these tests the speeds selected were 30
km/
h, 50
km/
hand sometimes 70
km/
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.
CHAPTER 4. METHODOLOGY
Test track layout Brushed old polished ice
100 m
Brake activation
marker
M
5 m
Vehicle tire paths
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 longitudinal
1direction 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.
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 satellites, this is done to lock onto as many satellites as possible. Speed accuracy is 0.1
km/
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 ev- ident 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.
4.2. CONDITIONS DURING TESTS CHAPTER 4. METHODOLOGY
10−Feb−2009 −30 11−Feb−2009 12−Feb−2009
−28
−26
−24
−22
−20
−18
−16
−14
−12
−10
−8
−6
−4
−2 0
Temperature (
°C)
0 10 20 30 40 50 60 70 80 90 100
Relative Humidity (%)
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].
4.3. DATA PRESENTATION CHAPTER 4. METHODOLOGY
10−Mar−2009 −10
−8
−6
−4
−2 0
Temperature (
°C)
0 10 20 30 40 50 60 70 80 90 100
Relative Humidity (%)
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 rate of deceleration in [
m/
s2]. In the graphs each vehicle is represented by a certain symbol.
Symbol size represents three speeds: 30
km/
h, 50
km/
h, and 70
km/
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.
Chapter 5
Results
Results will be presented according to the following list:
• Tests from 30
km/
hand 50
km/
hto 0
km/
h, during March 10, 2009 on brushed old polished ice.
• Tests from 30
km/
hand 50
km/
hto 0
km/
h, during February 11, 2009 on brushed old polished ice.
• Tests from 30
km/
hand 50
km/
hto 0
km/
h, during February 11, 2009 on brushed old polished ice.
• Tests from 30
km/
hand 50
km/
hto 0
km/
h, during February 12, 2009 on brushed old polished ice.
• Tests from 70
km/
hto 0
km/
h, during February 12, 2009 on brushed old polished ice.
• Tests from 30
km/
h, 50
km/
hand 70
km/
hto 0
km/
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.
5.1. BRUSHED OLD POLISHED ICE, MARCH 10, 2009 CHAPTER 5. RESULTS
A2 C2 F5 0
10 20 30 40 50 60 70 80 90 100
V70 Ford Mondeo
Braking distance [m]
2009−03−10, braking distances on polished ice at 30km/h
1 2 3
0 0.2 0.4 0.6 0.8 1
A C F V70 Ford
Figure 5.1: Stop distances on brushed old polished ice at 30
km/
h, March 10, 2009. Bars represents average stop distances, horizontal lines represent two standard deviations
Stop distances are similar in proportion at 30
km/
h(Figure 5.1), compared to results at 50
km/
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.
A2 C2 F5 0
10 20 30 40 50 60 70 80 90 100
V70 Ford Mondeo
Braking distance [m]
2009−03−10, braking distances on polished ice at 50km/h
1 2 3
0 0.2 0.4 0.6 0.8 1
A C F V70 Ford
Figure 5.2: Stop distances on brushed old polished ice at 50
km/
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 per-
formance 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.
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 11
th.
A1 B1 D1 A3 B3 E3 A4 B4 D4
0 10 20 30 40 50 60 70 80 90 100
C30 XC70 XC90
Braking distance [m]
2009−02−11, braking distances on polished ice at 30km/h
1 2 3
0 0.2 0.4 0.6 0.8 1
A D E C30 XC70 XC90
Figure 5.3: Stop distances on brushed old polished ice at 30
km/
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
significantly better on polished ice than for any other tires we tested. Stop distance at 30
km/
h,
for the Volvo C30 with A1 tires are 38 % longer, compared to stop distances measured for the
Volvo XC90 with A4 tires. See Appendix E. The difference at 50
km/
hwas 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
5.3. BRUSHED OLD POLISHED ICE, FEBRUARY 12, 2009 CHAPTER 5. RESULTS
A1 B1 D1 A3 B3 E3 A4 B4 D4
0 10 20 30 40 50 60 70 80 90 100
C30 XC70 XC90
Braking distance [m]
2009−02−11, braking distances on polished ice at 50km/h
1 2 3
0 0.2 0.4 0.6 0.8 1
A D E C30 XC70 XC90
Figure 5.4: Stop distances on brushed old polished ice at 50
km/
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 11
thactually underestimated roadgrip with the A4 tire. Otherwise the D type tires perform similar and comparable to the tires A1 on the C30.
A1 B1 D1 A3 B3 E3 A4 B4 D4 0
10 20 30 40 50 60 70 80 90 100
C30 XC70 XC90
Braking distance [m]
2009−02−12, braking distances on polished ice at 30km/h
1 2 3
0 0.2 0.4 0.6 0.8 1
A C C30 XC90
Figure 5.5: Stop distances on brushed old polished ice at 30
km/
h, February 12, 2009. Bars represents average stop distances, horizontal lines represent two standard deviations.
In Figure 5.6 the same pattern can be seen at 50
km/
has for the results at 30
km/
hpreviously.
A brand tires outperform the rest, and the B and D brand give comparable results, even if the
5.3. BRUSHED OLD POLISHED ICE, FEBRUARY 12, 2009 CHAPTER 5. RESULTS
B1 tires do outperform the D1.
A1 B1 D1 A3 B3 E3 A4 B4 D4 0
10 20 30 40 50 60 70 80 90 100
C30 XC70 XC90
Braking distance [m]
2009−02−12, braking distances on polished ice at 50km/h
1 2 3
0 0.2 0.4 0.6 0.8 1
A B D C30 XC90
Figure 5.6: Stop distances on brushed old polished ice at 50
km/
h, February 12, 2009. Bars represents average stop distances, horizontal lines represent two standard deviations.
70
km/
htests 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.
A1 B1 D1 A3 B3 E3 A4 B4 D4 0
10 20 30 40 50 60 70 80 90 100
C30 XC70 XC90
Braking distance [m]
2009−02−12, braking distances on polished ice at 70km/h
1 2 3
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
A C30 XC90
Figure 5.7: Stop distances on brushed old polished ice at 70
km/
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.
5.3. BRUSHED OLD POLISHED ICE, FEBRUARY 12, 2009 CHAPTER 5. RESULTS
A1 B1 D1 A3 B3 E3 A4 B4 D4
0 10 20 30 40 50 60 70 80 90 100
C30 XC70 XC90
Braking distance [m]
2009−02−11, braking distances on rough ice at 30km/h
1 2 3 4
0 0.5 1 1.5 2 2.5 3 3.5 4
A B C E C30 XC70 XC90
Figure 5.8: Stop distances on brushed old system 2000 ice at 30
km/
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.
A1 B1 D1 A3 B3 E3 A4 B4 D4
0 10 20 30 40 50 60 70 80 90 100
C30 XC70 XC90
Braking distance [m]
2009−02−11, braking distances on rough ice at 50km/h
1 2 3 4
0 0.5 1 1.5 2 2.5 3 3.5 4
A B C E C30 XC70 XC90
Figure 5.9: Stop distances on rough old system 2000 ice at 50
km/
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.
5.3. BRUSHED OLD POLISHED ICE, FEBRUARY 12, 2009 CHAPTER 5. RESULTS
A1 B1 D1 A3 B3 E3 A4 B4 D4
0 10 20 30 40 50 60 70 80 90 100
C30 XC70 XC90
Braking distance [m]
2009−02−11, braking distances on rough ice at 70km/h
1 2 3 4
0 0.5 1 1.5 2 2.5 3 3.5 4
A B C E C30 XC70 XC90
Figure 5.10: Stop distances on rough old system 2000 ice at 70
km/
h, February 11, 2009. Bars
represents average stop distances, horizontal lines represent two standard deviations.
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
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.
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 mea- sure 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.
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, distribution@vv.se.
[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.
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
5.1 Stop distances on brushed old polished ice at 30
km/
h. . . . 13
5.2 Stop distances on brushed old polished ice at 50
km/
h. . . . 13
5.3 Stop distances on brushed old polished ice at 30
km/
h. . . . 14
5.4 Stop distances on brushed old polished ice at 50
km/
h. . . . 15
5.5 Stop distances on brushed old polished ice at 30
km/
h. . . . 15
5.6 Stop distances on brushed old polished ice at 50
km/
h. . . . 16
5.7 Stop distance on brushed old polished ice at 70
km/
h. . . . 16
5.8 Stop distances on rough old system 2000 ice at 30
km/
h. . . . 17
5.9 Stop distances on rough old system 2000 ice at 50
km/
h. . . . 17
5.10 Stop distances on rough old system 2000 ice at 70
km/
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
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
Appendix A
Tires
Label A1/A2 B1 D1 C2
Brand Bridgestone Continental GT GoodRide
Model Blizzak Nordic
WN-01 Viking Contact 5 Champiro WT-AX SW601
(Snowmaster)
Tire side
Thread
Size 205/55 R16 205/55 R16 205/55 R16 205/55 R16
Manufacture
date 11-2008 44-2008 21-2008 43-2008
Mounting
instruction Rotation Outside Outside Outside
Type WTSLR WTSLR WTSLR WTSLR
Country of
origin Europe Germany Indonesia China
Load rating 94R 94T 94H 91H
Thread depth 8.7 mm 8.2 mm 8.6 mm 7.5 mm
Verified on
STRO list yes yes yes Not on list
11These tires were imported from Europe as they not are on the STRO-list of approved winter tires.
Label A3 B3 E3
Brand Bridgestone Continental Wanli
Model Blizzak DM-Z3 4x4 Cross Contact
Winter Snowgrip
Tire side
Thread
Size 215/65 R16 215/65 R16 215/65 R16
Manufacture
date 29-2008 10-2008 34-2007
Mounting
instruction Rotation Outside Rotation
Type WTSLR WTSLR WTSLR
Country of
origin Japan Germany China
Load rating 98Q 98T 98H
Thread depth 10.3 mm 8.5 mm 7.7 mm
2Verified on
STRO list yes yes yes
28.1 mm in central furrow.
Label A4 B4 D4
Brand Bridgestone Continental GT
Model Blizzak DM-Z3 Viking 4x4
WinterContact Savero WT
Tire side
Thread
Size 235/65 R17 235/65 R17 235/65 R17
Manufacture
date 26-2008 28-2008 26-2008
Mounting
instruction Rotation Outside Rotation
Type WTSLR WTSLR WTSLR
Country of
origin Japan Czech Republic China
Load rating 108Q 104H 104T
Thread depth 10.0 mm 8.6 mm 10.9 mm
Verified on
STRO list yes yes yes
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
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
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
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
Accuracy 0.1
Km/
hUpdate rate 100 Hz
Maximum velocity 1000 Mph Minimum velocity 0.1
Km/
hResolution 0.01
Km/
hLatency 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
C.2 Certificates
Figure C.2: Certificate for V-Box3i
Figure C.3: Certificate for IMU02
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.
09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 0.5
1 1.5 2 2.5 3 3.5 4
Time of day [h]
Deceleration [m/s 2 ]
V70 C2 30km/h V70 C2 50km/h Mondeo F5 30km/h Mondeo F5 50km/h V70 A2 30km/h V70 A2 50 km/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.
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.
09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 0.5
1 1.5 2 2.5 3 3.5 4
Time of day [h]
Deceleration [m/s 2 ] C30 D1 50km/h
C30 D1 30km/h XC70 E3 50km/h XC70 E3 30km/h XC90 D4 50km/h C30 A1 50km/h C30 A1 30 km/h XC90 A4 50 km/h XC90 A4 30 km/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.
09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 0.5
1 1.5 2 2.5 3 3.5 4
Time of day [h]
Deceleration [m/s 2 ]
C30 D1 50km/h C30 D1 30km/h XC90 D4 50km/h XC90 D4 30km/h C30 B1 50km/h XC90 B4 50km/h C30 A1 70 km/h C30 A1 50 km/h C30 A1 30 km/h XC90 A4 70 km/h XC90 A4 50 km/h XC90 A4 30 km/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.
09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 0.5
1 1.5 2 2.5 3 3.5 4
Time of day [h]
Deceleration [m/s 2 ]
C30 D1 70km/h C30 D1 50km/h C30 D1 30km/h XC70 E3 70km/h XC70 E3 50km/h XC70 E3 30km/h XC90 D4 70km/h XC90 D4 50km/h C30 A1 70km/h C30 A1 50km/h C30 A1 30 km/h XC90 A4 70 km/h XC90 A4 50 km/h XC90 A4 30 km/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.
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 represented
1this 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 stan- dard deviation, all in meters.
Time Vehicle Tire Speed Dist. Dec. Temp. Relative
HH:MM:SS type index (
km/
h) ( m) (
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
HH:MM:SS type index (
km/
h) ( m) (
m/
s2) (
◦C) humidity
1If a fourth stop distance not are available, then only two measurements are presented
