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by Robert R. Scheibe Principal Mechanical Engineer, GT Engineering Affiliate Assistant Professor, Department of Mechanical Engineering University of Washington, Box 352600 Seattle, Washington 98195
Washington State Transportation Center (TRAC) University of Washington, Box 354802 University District Building 1107 NE 45th Street, Suite 535 Seattle, Washington 98105-4631
Washington State Department of Transportation Technical Monitor Kenneth C. Kirkland State Maintenance Engineer Prepared for Washington State Transportation Commission Department of Transportation and in cooperation with U.S. Department of Transportation Federal Highway Administration October 2002
WA-RD 551.1
Robert R. Scheibe
Washington State Transportation Center (TRAC) University of Washington, Box 354802 University District Building; 1107 NE 45th Street, Suite 535 Seattle, Washington 98105-4631
Agreement T2695, Task 21
Research Office Washington State Department of Transportation Transportation Building, MS 47370 Olympia, Washington 98504-7370 Keith Anderson, Project Manager, 360-709-5405
This study was conducted in cooperation with the U.S. Department of Transportation, Federal Highway Administration. Studded tires have generated much controversy over the years; a number of states have banned them, while others, including Washington, have restricted their use and passed legislation to require lighter-weight studs. This report reviews recent studies that have addressed the performance and safety of the current generation of studded tires as well as the new “studless” winter tires on late-model vehicles. The well-documented correlation between studded tires and pavement wear was not the focus of this work. The issues surrounding studded tire performance and safety are complex. From the standpoint of traction alone, studded tires, when new, often provide some benefit over other tire types on ice-covered roads when the temperature is near freezing. However, the advent of the new studless tires has diminished the marginal benefit, and recent studies suggest that the infrequent, narrow range of conditions necessary for benefit from studded tires may not outweigh their detrimental effect on traction in dry or wet conditions on certain pavement types. In addition, a host of primary and secondary safety factors are related to studded tire use, many of which are very difficult to quantify, including facets of driver behavior and safety perception.
Studded tire, traction, performance, safety, winter
No restrictions. This document is available to the public through the National Technical Information Service, Springfield, VA 22616
The contents of this report reflect the views of the authors, who are responsible for the facts and the accuracy of the data presented herein. The contents do not
necessarily reflect the official views or policies of the Washington State Transportation Commission, Department of Transportation, or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation.
....................................................................................................................................................................... WINTER TIRE PERFORMANCE............................................................................................... Temperature Effects and Road Conditions ................................................................................................ BIBLIOGRAPHY .................................................................................................................................................................................................... CONCLUSIONS ............................................................... Studded Tire Usage.................................................................................. Other Factors Affecting the Use of Studded Tires ................................................................ 3............................................ Driver Behavior ................................ Incidental Traction Improvements......................................................................... Other Performance Data from Alaska..............................................................................CONTENTS
Section EXECUTIVE SUMMARY . Suspended Particulate Matter ................ 1....................................................................... WINTER TIRE SAFETY ............................... BACKGROUND . APPENDIX B................................................................................................................................. REFERENCES............................................................................... 1995 Alaska Studies........................................................................................................................... APPENDIX A................................................... INTRODUCTION.................................................................... Frictional Characteristics ......... Fuel Consumption................
Page ix x 1 1 3 3 5 8 9 10 12 14 16 21 36 41 41 43 43 45 46 46 47 47 48 48 50 54 56 A-1 B-1
............................................................ 2............................................... Study Approach ..................... Conclusions........................................................................................... Swedish Road and Traffic Institute Study .............. Driving Hazards Caused by Pavement Wear.................................... Noise ............... State of Washington Laws Regarding Studded Tires ............................................................. 4........................................................................................... 5................................ History and Composition of Tire Studs ......................................................... Convenience and Mobility............................................. Pennsylvania Transportation Institute Study .. 1994 Alaska Studies............................................................................................................................................ The Effects of Studded Tire Use on Traffic Accident Risk...................................................................................... Other Studded Tire Regulations ......................................................................... Cost of Studded versus Studless Tires..............................
.......................3 km/h) Stopping Distances of Chevy Truck ............................ Fairbanks.. Temperature Effects on 25 mph (40................... Stopping Distances of Test Tires with All Vehicle Types Combined....FIGURES
Figure 1 2 3 4 5 6 7 8 9 10 11 Typical First-Generation Stud Profile....................... 35 mph (56.......... Stopping Distances for Various Tires on Slippery and Bare Pavement................................................... Anchorage ............................ Stopping Distances of Test Vehicles with All Tires Combined ................................... Starting Traction of Test Tires (Time to reach 20 mph (32................ Stopping Distances of Test Tires with All Vehicles Types Combined ............................................................................... Comparison of First-Generation Stud with Controlled Protrusion.......................................................................2 km/h)) with All Vehicle Types Combined....................................................................... Stopping Distances for Various Tires on Slippery and Bare Pavement......................................4 km/h) Stopping Distances from Task 3 with All Vehicle Types and Surface Conditions Combined....................... The Effect of Temperature on Traction for Studded and Non-Studded Tires
Page 4 4 23 25 26 29 32 34 37 38 40
............................. Average Winter Road Surface Conditions........... Averaged 25 mph (40................. and Bare Pavement Surfaces in Fairbanks........ Ice..... and Bare Pavement Surfaces in Fairbanks......... Maximum Starting Grades (percent) ... Stopping Distances for 25 mph (40................................... and Bare Pavement..............
Page 6 11 13 14 18 19 20 21 23 24 26 29 30 31 33 36 38
................................ and Bare Pavement..3 km/h) Stopping Distances from Task 6 ..... Alaska............................3 km/h) Stopping Distances from Task 1 ............................................................. Averaged 25 mph (40.............................................. Averaged Starting Traction (Time to Reach 20 mph (32...................................................... Task 5 ........ Maneuvers.... Task 4 .................................................................................... Maximum Speeds During Cornering (mph (kp/h)) .............3 km/h) on Packed Snow..... Vehicle Friction Factors for Various Vehicle and Traction Aid Configurations....... Icy........... Fairbanks .......... Averaged 25 mph (40.... Stopping Distances on Packed Snow..........TABLES
Table 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Historic Studded Tire Use Estimates (% of Vehicles) for Oregon ................................................................... Icy.................2 km/h)) from Task 1........................... Averaged 25 mph (40.....3 km/h) on Packed Snow.......3 km/h) Stopping Distances at Different Temperatures............................................... Friction Coefficients for Studded and Non-Studded Tires Under Various Conditions ........ and Conditions...................................... Averaged Stopping Distance from Task 3 ............................................................................ Anchorage..................... Stopping and Starting Traction Performance Comparison between New and Used (1000 mile/1610 km wear) Lightweight Studded Tires.......................3 km/h) Stopping Distances from Task 2 .............................. Alaska ......................................... Ice.................... Stopping Distances for 25 mph (40..... Starting Traction Tests on Packed Snow...
while others. The issues surrounding the use of studded tires are very complex. the cost of studded tires in comparison with new studless winter tires. as well as those equipped with the new “studless” winter tires such as the “Blizzak” made by Bridgestone/Firestone. the “safety” of studded tires as measured by traffic incident data. have placed restrictions on their use and passed recent legislation requiring lighter-weight studs to reduce pavement wear. the focus of this work was to review the latest findings regarding the performance of late-model vehicles equipped with the current generation of studded tires. There are also a host of secondary effects. reduced vehicle control on roadways rutted by stud wear.EXECUTIVE SUMMARY
This study presents an extensive review of publications documenting recent research on the performance and safety of studded tires. this report does not concentrate on pavement wear issues. including Washington. the potential for improved traction characteristics on roadways “roughened” by studded tire use. A number of states have banned them. Rather. and driver behavior while using studded tires based on drivers’ perception of safety. the increase in fuel
. Although a substantial volume of research has investigated the negative impact of studded tires on pavement. The use of studded tires has been controversial over the years. There are many factors to consider. involving not just the obvious competing advantages and disadvantages of improved icy-road traction performance versus the costly impact of pavement damage. including the introduction of suspended particulate matter (dust) from roadway wear. the conditions under which studded tires are compared with other tires. including the parameters that are used to define traction performance.
Studded tires produce their best traction on snow or ice near the freezing mark and lose proportionately more of their tractive ability at lower temperatures than do studless or all-season tires. CONCLUSIONS 1. The broader issue of safety is also addressed through presentation of the many complex issues surrounding studded tire use that have been raised by recent research worldwide. the increment usually was small. With less aggressive (lightweight) studs being mandated. and a discussion of the traction performance characteristics of studded versus non-studded tires under varying conditions. 2. and for ice at lower temperatures. 3.consumption for studded versus studless tires. For the majority of test results reviewed for snow. and with the advent of the new “studless” tire. since the early 1990s. a condition whose occurrence is limited. the traction benefit for studded tires is primarily evident on clear ice near the freezing mark. For those conditions in which studded tires provided better traction than studless tires. The precise environmental conditions under which studded tires provide a traction benefit are relatively rare. The maximum frictional gain (in comparison to nonstudded (not studless) tires) is found for new studded tires on smooth ice. such as the Blizzak. studded tires performed as well as or worse than the Blizzak tire. and the possible trade-off in the use of traditional snow-clearing methods. The traction of studded tires is slightly superior to studless tires only under an ever-narrowing set of circumstances. This report presents a brief history of studded tires and their usage. where x
. a discussion of the newer studded and “studless” winter tires.
other controllability penalties. However. acceleration. studless. Traction performance can be characterized in many ways. controllability. as the studs wear. or if the comparison is made with studless tires. studless Blizzak tires offered the best traction performance. when averaged across several vehicles. which in turn were 8 percent shorter than for all-season tires. and all-season tires performed nearly equally on snow. Though all factors are important. The use of two studded tires on the front of a vehicle produced stopping traction results on snow and ice that were about halfway between the result of four studded tires and four all-season tires. 7. cornering. as the temperature drops. However. studded. In one set of stopping distance tests in Alaska. 8. In another set of tests in Alaska.they have been shown to provide up to 100 percent gain in certain tests. 6. such as yaw instability. This may reduce the risk of drivers misjudging the necessary braking distance and may improve the braking potential for anti-lock brakes. Studded tires reduce the difference in friction factor between optimum-slip and locked-wheel braking in comparison to non-studded tires. 5. 4. On ice. should be considered. especially for braking on both packed snow and ice in comparison to studded tires (which were second) and all-season tires (which were last). including braking. stopping distances for studded tires were 15 percent shorter than for Blizzaks. the single best indicator of tire performance is braking distance and deceleration. xi
. the relative frictional gain of studded tires diminishes or becomes negative on roughened ice. and grade climbing.
(0. 2) they drive faster (because of a false sense of security or confidence).024 in. Studded tires may lose more of their tractive ability over time (from stud wear) than studless tires. the frictional effect from the studs becomes negligible. to 0.
11.01. When stud protrusion diminishes to 0. excessive road spray.
A number of driver behavior issues have been postulated that tend to affect the judgment of studded tire effectiveness. there is little difference in stopping distance between studded and non-studded tires.
Tractive performance of studded tires is sensitive to stud wear.
A Norwegian study concluded that the use of studded tires tends to reduce the accident rate by a small amount – from 1 to 10 percent. and premature damage to pavement markings. This is especially true for concrete. Tire tread wear (on studded tires) has relatively little frictional effect if stud protrusion is maintained at 0.
12.039 in. There is not consensus on these points: 1) drivers with studded tires care more about safety.
On bare pavement. and 3) drivers with non-studded tires avoid driving when weather is severe.9.1 mm).
The roughening of ice and pavement from studded tires provides a safety benefit for all vehicles (with and without studs) by helping to prevent formation of smooth. studded tires tend to have poorer traction performance than other tire types. for asphalt.043 in. glare ice. hydroplaning on accumulated water in the ruts.
.6 mm). (1.
14. hence they drive more safely.
Pavement rutting caused by accelerated wear from studded tires can cause the dangerous conditions of tramlining.
Suspended particulate matter from pavement dust created by studded tires and noise from studded tires are health concerns in heavily traveled urban areas.
The cost of studless tires is significantly higher than studded tires—by approximately 50 percent.
17.15. But the other effects of unevenness.
Studded tires increase fuel consumption by a small amount (~1. and ice are far more significant than this factor and can increase fuel consumption by 15 percent.
16.2 percent) over non-studded tires on bare roadways.
four-wheel drive. INTRODUCTION
Studded tires were introduced in the United States in the early 1960s. Numerous recent studies have documented the pavement wear caused by studded tires. that documents studies relevant to the new generation of lighter weight studs. studless winter tires. so these issues will not be presented here in detail. However. and they have been well accepted by the general public as a means of enhancing mobility. Studded tires are convenient. Rather. particularly from the past 10 years. this study focuses on the performance on various road surface conditions of studded tires as compared with that of other common winter tires. a review of studies that examined the complexities of evaluating the safety of studded tires is also presented. STUDY APPROACH The objectives of this study were accomplished by comprehensively reviewing literature reporting on studded tire performance research that was performed in the 1
. It encompasses a review of recent literature. Legislation in many states has banned or limited the use of studded tires and has mandated less aggressive studs in an effort to reduce costly pavement damage (see appendices A and B). relatively quiet and comfortable (in comparison to tire chains).1. and vehicles with front-wheel drive. and anti-lock brakes. They quickly became popular in the northern climes because they provided the motorist with a built-in traction aid without the installation headaches required by temporary aids such as tire chains. In addition to performance data. including all season radials and the new “studless” winter tires. studded tires have long been the source of considerable controversy.
Europe.and fourwheel-drive vehicles. Though some of the foundations for this study were developed from the 1960s through the 1980s. and studless winter tires. the focus was on more recent data. This research also sought data on the effects of recent developments on vehicle traction. and Japan.United States. including the more widespread use of front. mostly from the 1990s. Canada.
the rubber secures the jacket in place (Angerinos et al. The stud core. 1999).2.S.307 in. In Spokane. The tire stud consists of two basic parts that have varied in size. filling any space between the jacket and the rubber. or insert is situated within the jacket and protrudes from the tire to make contact with the pavement (Figure 1). both the weight and protrusion have been reduced. 1999).2 mm). BACKGROUND
HISTORY AND COMPOSITION OF TIRE STUDS After their introduction in 1963. studded tire use approached 30 percent of passenger vehicles by 1972. and composition over the years. The advent of the Controlled Protrusion (CP) 3
. a flange at the base of the stud jacket holds it in place. In this way. Currently. pin. weight. (7. and in Alaska. (2. and Vermont approximately 60 percent of passenger vehicles used studded tires (Malik 2000). The outside part of the stud is known as the stud jacket or sleeve. Conventional studs in the 1960s were approximately 0.8 mm) long. as stud weight and protrusion length were shown to be significant factors in pavement wear rates. After insertion of a tire stud (jacket and pin) into the tire. approximately 56 percent of passenger vehicles use two or more studded tires (Angerinos et al. with a protrusion of about 0. approximately 10 percent of passenger vehicles in western Washington use two or more studded tires and approximately 32 percent of passenger vehicles in eastern Washington use two or more studded tires. In many states.087 in. a “breakin” period occurs during which time the tire rubber completely surrounds the stud jacket. Since the 1970s. Montana. studded tires became popular with drivers across the U.
Figure 1.067 oz.7 to 1.059 to 0. Typical First-Generation Stud Profile (Angerinos et al. The weight of the conventional stud from the 1960s averaged approximately 0.059 in.3 grams).081 oz.9 grams) (Angerinos 1999). today.039 to 0.S. while the typical CP stud. 1999)
First-Generation Stud
CP Stud
Figure 2. (1.stud allowed for nearly a 40 percent reduction in pin protrusion to 0. weighs 0. which is the only stud in use in the U.5 mm) by using a tapered pin that is able to move back into the stud jacket as the tire rubber is worn (Figure 2). (2. Comparison of First-Generation Stud with Controlled Protrusion (CP) Stud (Angerinos et al.0 to 1. 1999)
and 32 percent used them in the eastern portion of the state (based on two studded tires per vehicle) (Angerinos 1999)./0.3 percent in 1974 to 3. most perceived that studded tire use had declined and that winter tire use had dropped to less than 10 percent for passenger cars (Angerinos 1999).025 oz.5 mm) and weigh approximately 0.95 gram) (Brunette 1995). According to a 1995 survey of the 25 northern states and four Canadian provinces.047 to 0. Washington usage was 35 percent in that survey. while the highest was found in Spokane (56 percent). The earliest data (NCHRP 1975) showed widely varying usage numbers across the northern United States and Canada. The survey sampled parking lots and garages in 14 locations.039 oz.In the Scandinavian countries.033 oz. in which vehicles equipped with studded 5
. as well as those with a lightweight metal jacket (0. (1. The lowest stud usage was observed in Puyallup (6 percent)./0. Testing in Scandinavia has shown reduced wear effects for studs with a lightweight plastic jacket (0. The most detailed examination of usage rates was found in Oregon. (1. additional efforts have been made to reduce stud protrusion and weight.7 gram). A WSDOT survey conducted during the winter of 1996-1997 showed that on average. Historical studded tire usage rates in Oregon show that usage was fairly constant or declined somewhat from 9.5 percent in 1989 (Table 1) (Malik 2000).2 to 1. 10 percent of passenger vehicles used studded tires in the western portion of Washington.059 in. Studs there now range in length from 0.1 grams). These rates were determined by moving traffic counts. ranging from 10 percent in Oregon to 61 percent in Alaska. STUDDED TIRE USAGE It is difficult both to obtain accurate estimates of the usage of studded tires in cold weather climates and to determine whether the use of studded tires is increasing or decreasing.
Mt.5 14.5 8. Historic Studded Tire Use Estimates (Percentage of Vehicles) for Oregon (Malik 2000)
Zone 1 2 3 4 Statewide 1973-74 1. This survey was conducted primarily to determine the effect of studded tires on pavement wear. midway between Portland and Salem to north.5 percent.2 6. not just the number of vehicles. A 1990 visual parking lot survey showed an increase in usage to 11.0 11.6% Dec. 10-15 miles inland from coast Zone 2: Western valley bordered by Cascase range to east. 1989 1. bordered by Zone 1 to west.0 9.8 5.5%
Zone 1: Entire state coastal zone. 1990 Mar.8 11.4 1. a considerable increase from the 1970s when the 6
.2 6.4 5.usage rates appeared to climb.3 10. Zone 3: Northwest quadrant of state.tires were distinguished audibly from those that were not.2% 1983-4 3.5% 4.9% 2.0 24. Then.6% 3. This technique provided a means for developing an effective studded tires usage rate by accounting for the number of axles that used studded tires.5% 3.6 6. Zone 1 to west.7 14.1% 5.3 11. Washington state line to north Zone 4: Everything else
Extensive telephone and parking lot surveys conducted in 1995 and 1996 on behalf of the Oregon Department of Transportation indicated that studded tire use varied widely depending on the month and region being surveyed (Malik 2000). the usage rates were determined on a per-vehicle basis. Results showed that approximately half of vehicles in Oregon that were equipped with studded tires used them on both axles. including Portland.0 15.7 2.8% 0. Early surveys could not distinguish this difference. 1990 Parking Lot 1. Hence. California state line to south.4% Mar. Some of this may have been attributable to an increase in the number of vehicles that had studded tires on both axles instead of one. Table 1.0% 2.0 3. in 1990.7% 1983-4 1. Hood to east.
No data have been found to assess the usage rates of studless winter tires such as the Bridgestone/Firestone Blizzak. Hence.majority of vehicles installed studded tires only on the driving axle.
. it was necessary to account for the effective studded tire usage on a per-axle basis.5 percent. For the winter driving season of November through April. depending on who conducted the survey and how it as performed. the average effective studded tire usage rate statewide in Oregon ranged from about 16 percent to 23.
Determination of studded versus non-studded tire performance can be measured in a number of different ways. four-wheel drive) vehicle weight distribution brake system type (ABS or non-ABS) roadway pavement type and condition
. non-studded. which is more quantitative. as such. rear-wheel drive. Some of the metrics include straight line braking acceleration cornering controllability grade climbing. A multitude of variables will affect results. SUV) vehicle drive configuration (front-wheel drive. will be dealt with independently. was the focus of this work. including the following: initial speed (for braking tests) tire type (studded. though intuitively related.3. studless) number of studded tires (two or four) vehicle type (automobile. The performance of studded tires relative to non-studded tires. truck. WINTER TIRE PERFORMANCE
Studded tire performance and safety. are two different topics and.
packed snow. The static coefficient of friction is the ratio of the horizontal force that can be sustained by the tire
. Though this occurs under certain slippery conditions involving ice. tests over the years have shown that stopping distances are often increased on dry or wet pavement surfaces. near freezing. and cornering. acceleration. studroughened ice) temperature (above freezing. smooth ice. often represented by the coefficient of friction between the tire and roadway surface. for betterment of control during braking. and cornering. though relatively theoretical. To develop a comprehensive test matrix that would consider the effect of each of these variables would be a monumental task. acceleration.roadway surface condition (dry. loose snow. Studded tires were obviously intended to increase friction between tire and a driving surface. Instead. wet. including braking. well below freezing). studded tires do not necessarily shorten stopping distances. The traction performance of tires is primarily a function of the frictional characteristics between the tire and the driving surface. It has further been shown that under certain cold temperature conditions on icy roadways. is useful for predicting many facets of vehicle performance. This dimensionless value. and to our knowledge. most of these factors have been tested individually and in various combinations by a variety of researchers over many years. The results of some of those studies are presented below. has not been done. FRICTIONAL CHARACTERISTICS One measure of tire performance is through tire frictional characteristics.
that will be the case here also. or cornering divided by the vertical load (weight) on the tire. Connecticut. Because coefficient of friction represents a measure of only the specific interaction between the tire and roadway. Another study in Alaska stated that because of the temperature limitations on the effectiveness of studded tires (between 0 and 32 degrees F (–18 and 0
. it has been estimated that ice at or near freezing exists only 1 percent of the time in the State of Washington (WSDOT website). or drag factor. TEMPERATURE EFFECTS AND ROAD CONDITIONS Studs are most effective on ice at or near 32 degrees F (0 degrees C) and lose their efficacy as temperatures drop and the ice becomes too hard for the studs to grip or when temperatures rise and ice melts to slush or wet pavement. the term friction factor. other vehicle and environmental factors enter into the actual measurement of vehicle/roadway frictional performance. These data for Alaska and Minnesota. Friction factors for a tire undergoing braking. However. acceleration. accelerating. and cornering may be different.to the vertical force (usually weight) on the tire. but relative values for tires within each performance category should be comparable. and Minnesota are shown in Table 2 (Lu 1994). is sometimes used to represent the cumulative effect of all these variables and can be interpreted as the “effective” coefficient of friction. Friction factor can be defined as the force that can be generated by a tire (vehicle) in braking. it is difficult to measure in a practical sense. Hence. Some references use the terms coefficient of friction and friction factor interchangeably. both of which have harsh winters. show that the roads are icy only 12 to 13 percent of the time. Average winter road conditions in the states of Alaska.
Hence. Table 2. in comparison with studless tires. Again. The same source named a similar study in Ontario that examined average winter conditions for two years in the early 1970s.degrees C)). The temperature sensitivity of traction performance complicates the evaluation of studded versus non-studded or studless tires. That study showed that icy conditions prevailed for an average of 2. nor for icy roads near the freezing point. where studded tires have some recognized effectiveness. though no distinction was drawn between ice and hard-packed snow.15 percent of the vehicle miles traveled. Average Winter Road Surface Conditions (Lu 1994)
State Dry/Wet Pavement (%) 65 96. so the traction benefits from studded tires would likely accrue for even fewer miles than the reported 2. 11
.4 0. was likely to be considerably less than 13 percent.6 3 12 Icy Pavement (%) 12. their capabilities can only be used for 6 percent of the winter (Alaska Studded Tire Study 1973). tend to show advantages on ice near freezing and are at a disadvantage at temperatures well below freezing. Because studded tires. the total proportion of vehicle miles traveled on ice near the freezing point.15 percent. no distinction was drawn between ice near the freezing point and ice at lower temperatures. it is difficult to predict which tire will perform better unless temperature is part of the equation.5 13
Alaska Connecticut Minnesota
An older study reported that about 13 percent of all vehicle travel in Minnesota was on ice or hard-packed snow (NCHRP 1975).5 75 Snow/Packed Snow (%) 22.
studded tires. driving traction. Traction tests involved measuring the traction force while spinning the drive wheels of a vehicle that was either stationary or traveling. Locked wheel braking tests measured tire/roadway friction at 20 mph (32 kph). Anti-lock brakes showed benefit for controllability tests but not for locked-wheel braking or traction maneuvers.PENNSYLVANIA TRANSPORTATION INSTITUTE STUDY A study performed by the Pennsylvania Transportation Institute reported a comparison of friction factors for vehicles fitted with various traction aids on icy.
. snowy. four-wheel drive. Researchers performed tests and gathered published data to substantiate analytical estimates of friction factors for various tire and vehicle configurations. and anti-lock brakes. Not surprisingly. The results of the testing and analysis are summarized in Table 3. snow tires. or wet surfaces (Hayhoe and Kopac 1981). Their values measured braking. and “controllability” of the test vehicles equipped with standard highway tires. Results were similar for the traction and controllability tests. four-wheel drive was vastly superior for traction and controllability but offered no improvement in braking. Controllability values represented lateral tire frictional forces. Results showed that studded tires had slightly better locked-wheel braking performance (higher friction factor) on ice than highway or snow tires but were identical in performance to snow tires on snowy or wet surfaces.
15 0.12 0.024 0.03
Wet 0.08 0.6
Highway Tires Snow Tires (on rear only) Steel Tire Chains (on rear only) Studded Snow Tires (on rear only) Four-wheel Drive Anti-lock Brakes (4-wheel systems) Anti-lock Brakes (2-wheel systems)
Ice 0.19 0.4 0.19 0.3 0.16 0.Table 3.19 0.08 0.055 0.08 0.064 0.08 0.4 0.08 0.19 0.19 0.03 0.4 0.09 0.17 0.12 0.175 0.09 0. and Conditions1 (Hayhoe 1981)
Locked-Wheel Braking Ice Snow Wet 0. except where noted.4 0.13 0. ice temperature 25o F
.024 0.4 0.16 0.08 0.175 0.27 0.19 0.15
0.3 0.4 0.27 0.15 0.4 0.024
Traction Snow 0. Vehicle Friction Factors for Various Vehicle and Traction Aid Configurations.175 0.4
For rear wheel drive vehicle.37 0.175 0.055 0.8 0.4 0.15 0.19 0.8 0.4 0.15 0.024 0.19
Controllability Ice Snow Wet 0. Maneuvers.23 0.4 0.032 0.
Tests included optimum-slip braking.14-0.36-0.24-0.070 in.04) 0.03)
0. (1.20
(-0. tire wear.02-0. This research compared the frictional differences between studded tires and non-studded winter tires (intended to be studded).14 0. locked-wheel braking. New.07 0.12 0.10-0.2o to 6.38 0. ice condition (smooth versus stud-roughened).11 0.08
.26 0.14-0.21 0. and maximum cornering. It also considered the effect of stud protrusion (which includes the effect of stud wear).16-0.25
0.21-0.2-0.12-0.8oF (-1 to -14oC) Smooth Ice Optimum Slip Locked Wheel Maximum Cornering Temperature: : 30. Friction Coefficients for Studded and Non-Studded Tires Under Various Conditions (based on Nordstrom and Samuelsson 1991)
Friction Coefficient Temperature: 32oF (0oC) Smooth Ice Optimum Slip Locked Wheel Maximum Cornering Temperature: 32oF (0oC) Stud-Roughened Ice Optimum Slip Locked Wheel Temperature: 30.44 0.15-0.12-0.21-0.043 to 0.07 (-0.25 0.13
0.09-0.8oF (-1 to -14oC) Stud-Roughened Ice Optimum Slip Locked Wheel Non-Studded Tire Studded Tire 0.10 0.09-0.00-0.05 Friction Gain due to Studs
0.8 mm) were tested. and with stud protrusion of 0.10-0.05-0.1-1.07 0.2o to 6. and ice temperature.23
0.27 0.00-0. Table 4.12-0.27 0.33
0. fitted with 105 to 123 studs each. A partial summary of test results can be found in Table 4.02-0.17 0.12 0.09 0.10-0.02-0. studded tires.19 0.05-0.04-0.26
0.18-0.14-0.02-0.36-0.19 0.SWEDISH ROAD AND TRAFFIC INSTITUTE STUDY Another comparison of the frictional characteristics of studded and non-studded tires was performed by the Swedish Road and Traffic Institute (VTI) in 1988 (Nordstrom and Samuelsson 1991).
36 to 0.02 to 0. Typically. optimum slip occurs when there is between 10 and 15 percent wheel slippage (rather than 100 percent slippage.00 to 0. This occurred on smooth ice at 32 degrees F (0 degrees C). the greatest effective gain in friction coefficient (0.
. Key findings from the VTI study included the following: For the comparison of new studded with non-studded tires.13). a benefit of nearly 100 percent.07. the degree of deceleration achieved under such conditions is usually not as great as with optimum-slip braking.02-0.23).09 to 0. non-studded to studded tires was –0.38. For locked wheel braking under the same conditions. but the baseline friction coefficient was lower for non-studded tires (0. which occurs under locked-wheel braking).10) occurred for studded tires undergoing optimum-slip braking. particularly when temperatures were below the freezing mark. there was no frictional gain from studded tires.11. the frictional change from new.20-0. Locked-wheel braking is when all four wheels are arrested. the friction gain was higher for studded tires (0. On 32 degree F (0 degree C) ice roughened by studs. The friction gain due to studs was modest at 0.04. where the friction coefficient for non-studded tires was 0. the friction coefficient for new. Under certain conditions. For example. note that optimum slip is defined as the degree of brake application necessary to achieve maximum deceleration (or maximum coefficient of friction).In reviewing Table 4. non-studded tires under optimum-slip braking was 0. The purpose of ABS is to automatically optimize slip while braking. on ice roughened by studs at temperatures between 14 and 18 degrees F (–10 and –8 degrees C). both for maximizing deceleration and for enhancing vehicle stability and control.
which include test data as well as a review of data from other 16
.The frictional effect of studs becomes negligible when stud protrusion drops to about 0. of the Transportation Research Center at the University of Fairbanks. Studded tires are most beneficial when used on wet.043 in. the effect of worn tires is not nearly so pronounced. or on colder ice with surface contamination from snow or ice powder. Lu’s work was performed in the mid 1990s. Mr. Friction generally increased with increasing ice roughness. this benefit greatly diminished when ice temperatures dropped below freezing. This suggests a benefit to traction for vehicles not equipped with studded tires when they travel on icy roads previously traversed by vehicles with studded tires.197 in.039 to 0. (0.1 mm) yield friction values similar to that of a new studded tire under the same conditions. However. In contrast.6 mm). This could reduce the risk of misjudgment of necessary braking distance and may improve the braking potential for anti-lock brakes. (1. 1994 ALASKA STUDIES Of the researchers of studded tire performance over the past 10 to 15 years. the friction factor for both studded and non-studded tires at least doubled on roadways with roughened ice as compared with smooth ice.0-1. On 32 degree F (0 degree C) “wet” ice. The highlights of his work. On smooth ice under optimal-slip braking. perhaps the most prolific was Jian John Lu. clear ice near 32 degrees F (0 degrees C). (5 mm) tread depth with stud protrusion of 0. Alaska. stud protrusion has much more influence than tire wear under these circumstances. Hence. Studded tires reduce the difference in friction factor between optimum-slip and locked-wheel braking more than do non-studded tires.024 in. studded tires worn to 0.
Studless winter tires. These tires incorporate an aggressive. * Other studless winter tires (Q-rated/Snowflake symbol)
Bridgestone Blizzak MZ-01 Bridgestone Blizzak MZ-02 Bridgestone Blizzak WS-15 (original) Bridgestone Blizzak WS-50 Bridgestone Blizzak W965 (Light Truck) Bridgestone Winter Dueler DM-Z2 (Light Truck) Dunlop Graspic DS-1 Dunlop Graspic HS1 / HS2 Dunlop Grandtrek SJ4 (Light Truck) Goodyear Ultra Grip Ice Michelin Arctic-Alpin Michelin 4X4 Alpin (Light Truck) Pirelli Winter Ice Asimmetrico Pirelli Winter 210 Performance Ice Yokohama Guardex 600 Yokohama Guardex RV F340
. The work performed by Mr. and many studies have sought to compare the performance of the Blizzak with that of studded tires on ice and packed snow surfaces. with conventional studded tires and all-season tires. deep tread design in a soft rubber compound with multiple sipes and. one of a series of modern “studless” snow tires developed for increased winter traction. The Blizzak is one of the more popular alternatives to studded tires.sources. The tests compared the effects of the Bridgestone/Firestone “Blizzak” tire. in the case of the Bridgestone Blizzak. micro-bubbles that provide tiny gripping edges on ice*. Lu is particularly relevant to the present study undertaken by the State of Washington because it represents a recent examination of the performance issues of the latest generation of studded and studless radial tires on contemporary vehicles with such characteristics as front-wheel drive and anti-lock brakes. developed in the early 1990s. Tests were conducted by the University of Alaska at Fairbanks in the spring of 1994 (Lu 1994). will be presented here along with findings from other sources. represent a new class of tire dedicated to winter travel.
5) 63.5 (35.2) 16.0) 117.0 (38.0 (21.6 (20. results are shown in tables 5 and 6.7 (15.5) 57. showing 15 percent shorter stopping distances than the Blizzaks.5) 59.9) 69.2 (18.6) 64.9) 17.1)
122.2) 116.7 (46.5 (39. ice.1 (19.4 (17.3)
104.5) 2 Wheel Rear Wheel Drive Pickup Drive Car 79.5 (19.0 (19.6) 105.3 (19. and Bare Pavement Surfaces in Fairbanks. while the stopping distances of the all-season radials were 8 percent longer than the Blizzaks. Table 5.3 (4.7) 128.1)
Bare Pavement Surface Blizzak Tire Studded Tire All-Season Tire
16.0 (25.4 (39.2) 118.1 (32. Alaska (based on Lu 1994)
Front Wheel Drive Car Packed Snow Surface Blizzak Tire Studded Tire All-Season Tire Icy Surface Blizzak Tire Studded Tire All-Season Tire 62.9) 17. 2) a two-wheel-drive.3 (24.2) 68.6 (5.1 (19. the studded tires were superior.7 (35. For bare pavement.6 (5. full-size Chevrolet pickup truck equipped with ABS. and bare pavement using 1) a front-wheel-drive Chevrolet Lumina equipped with anti-lock brakes (ABS).3) 127.0)
16.0) Average
50.Tests were conducted at the Fairbanks International Airport under conditions of packed snow.0)
Note: all vehicles equipped with ABS
Stopping distance results averaged across the three vehicles showed that on packed snow there was little to distinguish one tire from another.0 (5.4 (18.9) 64.4) 64.0 (37.9) 106.5) 152.0 (5. and 3) a rear-wheel-drive Chevrolet Caprice with ABS. Icy.2 (36. Stopping Distances (feet (m)) on Packed Snow.3 (4.1) 64. Stopping distances and starting traction were recorded and averaged. the stopping distances of the three tires (tested only on the pickup) were
.4) 84.5)
128. On ice.2) 16.5 (32.0 (31.
42 10.88 sec Studded Tire 9.41 11.08
17. On ice. traction was defined by the time (in seconds) it took for the vehicle to accelerate from a standstill to 25 mph (40.57 10. The longest stopping distance was for the studded tires.53 10.49
12. and Bare Pavement Surfaces in Fairbanks.74 3. Table 6. The all-season tires were slightly behind.99 Average
9. Starting Traction Tests (Time to Reach 25 mph (40. respectively.6 sec 9. the studded tires and Blizzaks were very similar.12 10.5 sec 8.and rear-drive cars equipped with studded tires held a clear advantage over the Blizzaks and all-season tires. All the tests were relatively vehicle and driver dependent. But on the pickup.41 sec 9.03
For the starting traction tests.52 3.01 18. Results.3 km/h). but only by 2 percent over the all-season radials and 5 percent over the Blizzaks.12 and 9.7 9. Icy.94 12.49 seconds.63 19.27 All-Season Tire 10. and both showed superior traction
.52 3. These differences may not be significant.53 13. showed that for packed snow.74 3.3 km/h)) (sec) on Packed Snow. the studded tires provided traction very similar to that of the Blizzaks.86 16. shown in Table 6. at 9.6 seconds.94
13 12. which is marginally significant.73
3. front. at 10.very similar. Alaska (Lu 1994)
Front Wheel Drive Car Packed Snow Surface Blizzak Tire 8.06 Icy Surface Blizzak Tire Studded Tire All-Season Tire Bare Pavement Surface Blizzak Tire Studded Tire All-Season Tire 2 Wheel Rear Wheel Drive Pickup Drive Car 9.
40. Maximum lateral acceleration on snow was found to be 0.2) 9.7 m) and 50 ft (15.8 (19.6) Ice on Pavement 14. Lateral acceleration was measured with instrumentation. but about 13 percent less than for the all-season tires. Tests were also conducted by the University of Alaska at Fairbanks to investigate cornering and hill climbing ability.7)
. however.7 (22. while the Blizzak was approximately 7 percent faster.6) All-Season Tires 17. Results summarized in Table 7 show that studded tires generally had the lowest cornering speeds.9 (25.7) Studded Tires 15.9) 13.8) 10. For the cornering tests.9 (17. Table 7. and maximum cornering speeds were calculated from the data.2. Variations were not large.25 to 0.6 (21.4 m) Curve
Blizzak Tires 17.0
Blizzak Tires 12.5) Studded Tires 10.5) All-Season Tires 11.2 (27.3 (16.0) 50-ft (15. The studded and all-season tires had nearly identical results. It is not clear whether this difference is significant.4 m) while lateral acceleration was recorded. the Blizzak traction times to reach 25 mph (40.2 (22.1 (16. and the Blizzak generally had the highest.1 (19.7 m) Curve Packed Snow Ice on Pavement 10. only the pickup was used. and on ice was 0.3 km/h) were about 18 percent longer than those for studded tires.8) 13.to the all-season tires by about 40 percent. On the average for all vehicles.1 to 0. and not likely significant.2 (27. the vehicles were operated on curves with radii of 25 ft (7. Maximum Speeds During Cornering (mph (kp/h)) (based on Lu 1994)
25-ft (7.8 (15. On bare pavement. however.
additional testing was performed there in 1995 (Lu 1995) to validate previous results and to consider other factors. Maximum starting grades are summarized in Table 8 for tests on packed snow. ice on pavement. including 1) the effects of used (worn) winter tires on traction performance 2) the performance of lightweight studded tires
. Tests determined that both the studded snow tires and the Blizzaks had similar grade climbing capability in packed snow. Maximum Starting Grades (percent) (Lu 1994)
Packed Snow Fairbanks Results Blizzak Tires Studded Tires All-Season Tires Anchorage Results Blizzak Tires Studded Tires All-Season Tires Ice on Pavement 11% 12 10
16% 16 15
1995 ALASKA STUDIES As a continuation of the 1994 research project in Alaska.Gradability was analytically determined by measuring the longitudinal acceleration during traction tests in both Anchorage and Fairbanks.
Table 8. Both the studded snow tires and the Blizzaks were superior to the all-season tires for grade climbing. but the studded tires had a slight advantage in icy conditions. and lake ice.
The air temperature during testing was reported to be below 10 degrees F (-12 degrees C). which were mostly conducted on airport taxiways. Alaska. The tires had accrued more than 1000 miles (1610 kilometers) of wear since they were originally tested in 1994.3) the performance of a front-drive car and a rear-drive pickup with studded tires on only the two front wheels 4) the effect of tire wear and pavement surface temperature on traction performance 5) vehicle controllability (lateral traction) performance tests 6) the effect of vehicle type on traction performance. and a rear-wheel-drive Chevrolet Caprice with four-wheel ABS. to more closely simulate real roadway conditions. The purpose of the first task was to explore the effect of tire wear on braking and starting traction. For the braking traction tests. the shortest stopping distance for the snowy surface was from the Blizzaks. which were 9 to 13 percent better than the studded tires and 18 to 24 percent better than the all-season tires.3 km/h). stopping distance and maximum deceleration were measured after brakes were applied (in an effort to lock the brakes) on vehicles traveling 25 mph (40. Unlike the tests conducted in 1994. two-wheel-drive Chevrolet pickup truck with ABS on only the rear wheels. the vehicles tested included a Chevrolet Lumina without ABS. When results for the first task were averaged for all three vehicles. For all tasks. a full-sized. tests for this study were primarily conducted on roads and parking lots around Fairbanks. The first task involved traction performance tests on snowy and icy surfaces with the same tires that had been tested in 1994 (which were new at that time). 22
Table 9.8) 91.9 (33.7 (24.2 (20.1) Caprice 50.9 (27.6 (26.9) Pickup 72.5)
71.1) 109.7) 114.8 (29.2 (27.2 (21.5 (34.3) 63. but both were approximately 25 percent better than the all-season tires.1) 82.4) 104.On the icy surface.7 (25.2) 88.5) 69. Table 9 and Figure 3 show the results of these tests.5) 90.5) 89. corresponded predictably to the braking traction results and hence are not presented here.2 (27.7) 76.8) 78. Averaged 25 mph (40.7 (25.2) 96.9 (19.1 (23.9 (27.3) Average 68.5 (22.9)
81.5)
40 Packed Snow Surface 35 30 Stopping Distances (m) 25 20 15 10 5 0 Blizzaks Studded Tires All Season Icy Surface
Figure 3. the Blizzaks and studded tires were more closely matched.2 (27.2 (15. Stopping Distances (m) of Test Tires with All Vehicle Types Combined (Lu 1995) 23
.7) 128.6 (31. Maximum deceleration for the three tire types.6 (26.1)
83.1) 87.8)
90. averaged across each vehicle.3 (39.8 (23.3 km/h) Stopping Distances ft (m)) from Task 1 (based on Lu 1995)
Snowy Surface Blizzaks Studded All Season Icy Surface Blizzaks Studded All Season Lumina 82.9 (21.9) 85.3 (25.
18 11.14 7.53 11.3
7. slightly ahead of studded tires.2 km/h).9 Average 7.18
7.95 8.19 10. Both these tire types performed considerably better than all season tires (11 percent better on snow and 25 percent better on ice).15
8.67 sec 7.84 8.07 Caprice 7.35 9.2 km/h)) (sec) from Task 1 (based on Lu 1995)
Snowy Surface Blizzaks Studded All Season Icy Surface Blizzaks Studded All Season Lumina 7. Braking tests were conducted in the same manner as previously—on both a packed
. Averaged Starting Traction (Time to reach 20 mph (32. The studded tires appeared to lose proportionally more of their traction capability than did the other tires. regardless of whether they were tested on snowy or icy surfaces.58 Pickup 8.94 sec 8. The second task of the 1995 Alaska study (Lu 1995) compared the stopping traction performance of new “lightweight” studded tires (with aluminum studs) that have been developed in response to concerns about pavement damage from conventional steel studs.65 sec 8. each vehicle was accelerated at maximum rate from a standstill and timed until it reached 20 mph (32.17 8.02 9. Results (Table 10 and Figure 4) showed that nearly the same starting traction performance was obtained for the studded tires and the Blizzaks.86 9.Starting traction performance tests were conducted similarly to those in 1994.71
The conclusions from these tests were that the Blizzaks offered the best overall traction performance on both packed snow and icy surfaces.68
7.98 8. but both the Blizzaks and the studded tires performed considerably better than the all-season tires.54 9. Table 10.51 sec 8.
3 km/h). Starting Traction of Test Tires (Time to reach 20 mph (32.
Packed Snow Surface
Time to Reach 32. On an icy surface. with the driver attempting locked-wheel stops from 25 mph (40. the standard studded tires and Blizzak tires were the same (used) tires that had been tested previously in this program and in the 1994 program. Air temperature during these tests was about 0 degrees F (-18 degrees C). and about 16 percent behind the Blizzaks were the standard-studded tires. the 25
. About 10 percent behind the Blizzaks were the lightweight-studded tires.2 km/h)) with All Vehicle Types Combined (sec) (Lu 1995) Stopping traction test results (Table 11 and Figure 5) showed that on a packed snow surface. the Blizzaks had the shortest stopping distance of the three tires tested.snow surface and an icy surface. Two vehicles were used: the full-sized Chevrolet pickup and the Chevrolet Caprice. The tires with lightweight studs were new.2 km/h (sec)
0 Blizzaks Studded Tires All Season
Stopping Distances (m) of Test Tires with All Vehicle Types Combined (Lu 1995)
.6) 70.3 km/h) Stopping Distances (ft (m)) from Task 2 (based on Lu 1995)
Snowy Surface Blizzaks Standard Studded Lightweight Studded Icy Surface Blizzaks Standard Studded Lightweight Studded Pickup 72.7 (24.9 (20.9) 65.3) 69.1) 83.1 (23.6) 52.7)
82.2 (15.3 (12.8) 70.3) 71.5 (22.6 (25.3 (26.9 (21.4 (16.5)
30 25 Stopping Distance (m) 20 15 10 5 0
Packed Snow Surface Icy Surface
Standard Studded Tires
Lightweight Studded
Figure 5.5 (16.4 (24. Table 11.3 (25.4) Caprice 40.2) 84.3)
76.lightweight-studded tires showed the best stopping traction.0) Average 55.3) 51.0 (25.1) 80.1) 61. Averaged 25 mph (40.3 (18. with braking distances approximately 11 percent shorter than the Blizzaks and about 17 percent shorter than the standard-studded tires.5 (21.2 (21.2) 86.2 (21.
3 km/h). instead of all four tires. on just the front wheels (with all-season tires on the rear) and with all-season tires on all four wheels. the 1995 Alaska research also examined the braking traction performance of two studded tires only. which may have affected the results. On ice. as had been the case for all previous testing. the lightweight studded tires generally produced the best stopping and starting traction performance when compared with the Blizzaks and standard-studded tires. the greatest acceleration came from the standard studded tires. Comparisons were made for each vehicle equipped three different ways: standard studded tires on all four wheels. while the lightweight-studded tires were new. followed by the Blizzaks. In conclusion. followed by the lightweight-studded and standard-studded tires. These tests were apparently conducted because the option of running two instead of four studded tires has been considered for reducing pavement wear. the Blizzaks had the greatest deceleration. But the greatest acceleration on snow came from the Blizzaks. Two vehicles were tested. but the value was nearly identical to that of the Blizzaks. followed by the lightweight-studded tires. In a third task. the lightweight-studded tires had the greatest deceleration followed by the Blizzaks and standard-studded tires (the latter two of which were nearly equal). Tests were only for braking traction (not starting 27
. However. the Blizzaks and standard-studded tires were somewhat worn. a front-wheel drive Chevrolet Lumina with ABS and a full-sized (rear-wheel drive) Chevrolet pickup truck. mounted to the front wheels. On ice.Stopping traction results measured with an accelerometer yielded results consistent with the stopping distance measurements: on snow. Starting traction performance produced similar results: the lightweight-studded tires on snow and ice required the shortest time to reach 25 mph (40.
would be the directional stability.
. for rear-wheel drive vehicles such as the pickup truck. When test results from both snowy and icy surfaces were averaged (Table 12 and Figure 6). Presumably. particularly under braking and/or cornering. and about 7 percent worse than the vehicle with all four studded tires. the vehicle with two front studded tires performed about 8 percent better than the vehicle with four all-season tires. starting traction performance would not be enhanced if studded tires were placed only on the front (non-driving axle).” while decelerating or cornering. This result confirms a fairly predictable outcome: when two studded tires are placed on the front wheels. under certain conditions. If the studded tires were placed only on the rear of the rear-wheel drive pickup. However. could become unstable in yaw if mismatched tire types were mounted front to rear. This could cause the vehicle to become directionally unstable and to rotate about a vertical axis. however. Obviously.traction) and were conducted similarly to those performed previously except that a 35 mph (56. when tires of different friction factor were used in the front and rear. It is possible that various vehicles. the use of two versus four studded tires would provide a commensurate decrease in pavement wear. the benefit to braking traction is roughly half of the benefit if studded tires are used on all four wheels. further thought and testing must be applied to determine whether such a practice also may compromise other facets of vehicle performance.4 km/h) initial speed was used. it is likely that the braking traction performance would not have been enhanced as much as with the studded tires in front (because of the forward weight distribution). or “spin out. A more serious concern.
5) 100.5 (34.3)
34 33 Stopping Distances (m) 32 31 30 29 28 27 26 Four Wheel Studded Standard Studded Tires Lightweight Studded
Figure 6.3 (28.9) Total Average 93. For the tire wear tests.7) 109. the same lightweight-studded tires tested while new in the second task were driven 1000 miles (1610 km) on the road.6) Icy Surface Average 127.8) 101.2) 99. Averaged Stopping Distance (ft (m)) from Task 3 (based on Lu 1995)
Tire Type Four Wheel Studded Standard Studded Lightweight Studded Snow Surface Average 92.4) 113. 1995) included an examination of the effects of tire wear and surface temperature on stopping and starting traction.5 (28.6 (31.Table 12.3 km/h) and starting traction times to the same speed were measured on a packed snow surface at
.7 (30. 35 mph (56.7 (31.4 km/h) Stopping Distances (m) from Task 3 with All Vehicle Types and Surface Conditions Combined (Lu 1995) The fourth task of the Alaska study (Lu. Stopping distances from 25 mph (40.5 (28.0) 104.7 (30.2 (33.
73 sec 55. This confirmed that tire and stud wear diminish the traction performance capability of the tires. A more formal test of the effect of temperature was performed as part of the fourth task.3 km/h) 48. Results (Table 13) showed that after accruing tire wear through use. Stopping distances were 6 percent longer at the colder temperature (for the “new” tires on a packed snow surface). stopping distance data at 25 mph (40.3 km/h) were collected for the full-sized Chevrolet pickup on packed snow and icy surfaces at temperatures 30
.7) 6.3 km/hr) (40.9 sec 12% 2%
Caprice on packed snow surface. wherein new lightweight-studded tires were tested on the Caprice.about 32 degrees F (0 degrees C) both before and after the tires had been “worn” on the road. whereas the tests for the fourth task were run at the freezing mark. the effect of temperature was noted. Only the Chevrolet Caprice was used for this comparison. 32°F.1 (16. Table 13. the lightweight-studded tires required about 12 percent longer distances to stop from 25 mph (40. Task 4 (based on Lu 1995)
Studded Tire Type Stopping Traction Starting Traction
New Lightweight Old Lightweight Difference
Stopping Distance (ft/m) Time (sec) to from 25 mph Reach 25 mph (40. (0°C)
Upon comparison with the second task.3 km/h) and about 2 percent longer to attain this speed than when they were new.8) 6. Stopping and Starting Traction Performance Comparison between New and Used (1000 mile/1610 km wear) Lightweight Studded Tires1. Tests from the second task were run at temperatures of 0 degrees F (–18 degrees C). For these tests.2 (14.
2) 88. The only exception was the allseason tire on ice.8) 85.7 (25.3 (25.5 (22. Three tire types were tested: standard studded tires. Results generally showed that stopping distances were shorter at temperatures near freezing than at –20 degrees F (-29 degrees C). With all vehicles and surface conditions combined and the results averaged (Table 14 and Figure 7).4 (23.5)
2% 7% -6%
78. Especially for ice near freezing.7 (24. the traction of the studded tires is particularly enhanced because of the more aggressive engagement in the ice by studs. Averaged 25 mph (40.8 (28. Table 14.3) 103.7 (23. the potential benefit from studs becomes less apparent as temperature drops.5 (22.3 km/h) Stopping Distances (ft (m)) at Different Temperatures.1) 80.3)
77.1 (23. and all-season tires. Blizzaks.9 (26.7 (25.2) 96.2 (27. which stopped 6 percent shorter at the colder temperature.3 (31. the snow and ice are warmer and hence softer.0 (25.8 (29.0) 90.5) 89.6)
.7) Difference 0% 2% 12%
83.6) 77.5 (27.1) 82.6) 82. One possible explanation for this is that at the higher temperatures.9 (27. Task 5 (based on Lu 1995)
Snowy Surface Blizzaks Standard Studded All Season Icy Surface Blizzaks Standard Studded All Season Snowy-Icy Combined Blizzaks Standard Studded All Season Temp: -20°F (-29°C) 72.2) 92.1) 83.1) Temp: 32°F (0°C) 72. This differential was more than twice that of the all-season tires and five times that of the Blizzaks. the studded tires showed the most significant difference—with 5 percent shorter average stopping distances at temperatures near freezing.0 (25. Thus.of -20 degrees F (-29 degrees C) and 32 degrees F (0 degrees C).5)
the test vehicles were fitted either with Blizzaks.4 km/h) on both snow and ice at temperatures near freezing. however. or two studded (front) and two all-season tires.Averaged 40.3 km/h Stopping Distances (m)
29 28 27 26 25 24 23 22 21 Blizzaks Studded Tires All-Season -20 deg F 32 deg F
Figure 7. the vehicle equipped with four studded tires had the best lateral traction performance (the least lateral displacement and least angular rotation). A video camera recorded the vehicle trajectory. the all-season tires were next. They were stopped from 35 mph (56. Results showed that for snow and ice combined. 32
. In these tests. four studded tires. and later analysis of the video tape allowed measurement of the maximum lateral displacement and maximum angular directional change. Temperature Effects on 25 mph (40. Results were very close. and the differences were not particularly significant. and the other two groups followed.3 km/h) Stopping Distances (m) of Chevy Truck (Lu 1995) The fifth task of the 1995 Alaska study examined vehicle lateral controllability during stopping maneuvers. all-season tires.
9 (27.1) 50.4 (24.1) 96.5) 69. Averaged 25 mph (40. the Caprice stopped in the shortest distance. rear-wheel drive.2 (21. allseason tires. Tests were conducted with standard studded tires. particularly vehicle weight distribution.0 (31. half-ton Chevrolet pickup. stopping and starting traction were compared for the front-wheel drive Chevrolet Lumina.9 (21. and suspension dynamics.4) 84. ahead of the Lumina by 3 percent and the Caprice by 6 percent. A number of vehicle factors probably contributed to this difference.5) 89.6 (26.5) 104.7) 76.3) Average 94. the truck had the best performance.For the sixth task in the 1995 Alaska study.9) 81. and rear-wheel drive Chevrolet Caprice.7)
.3 (39. and Blizzaks on snow and ice at very low temperatures of –20 to –30 degrees F (-29 to –35 degrees C).9)
103.3 (18.4) 89.2 (27.8 (23. In these tests. Table 15.9 (27. Drive configuration is not likely to have played a part in this disparity because the vehicles were being braked. the effect of vehicle type and drive configuration on traction performance was examined.9 (27.3 (25.8 (28.3 km/h) Stopping Distances (ft (m)) from Task 6 (based on Lu 1995)
Snowy Surface Lumina Chevrolet Pickup Caprice Icy Surface Lumina Chevrolet Pickup Caprice Blizzaks 82.7 (25. as were times to reach 20 mph (32.2 (15. ahead of the truck by 15 percent and the Lumina by 26 percent. tire size and contact area.5 (34.9 (19.3 (25.6 (31.3 km/h).2) 88.7) 114.5 (22. Stopping distances were measured for initial speeds of 25 mph (40.9) 82. For starting traction tests.8 (29.1) 72.7 (25.2 (27.2 km/h) from a standstill.4)
128. Results averaged across all conditions and tire types (Table 15 and Figure 8) showed that for the stopping traction tests.7) 83. The spread in results was not significant and was likely the result of experimental technique and the variation in vehicle parameters discussed above.3) Studded All Season 87.8) 61.5) 90.2) 71.7)
90.1) 63.
Studded tires may lose more of their tractive ability over time than Blizzaks. though this conclusion may have been confounded by the fact that the lightweight studded tires were new.
. 2. though performance differences for the studded tires and Blizzaks were not significantly different. The non-studded Blizzak tires offered the best traction performance. Stopping Distances (m) of Test Vehicles with All Tires Combined (Lu 1995) The following overall conclusions were drawn from the Alaska Studies (Lu 1995): 1. while the other tires tested had been worn somewhat.35 30 Stopping Distance (m) 25 20 15 10 5 0 Lumina
Snowy Surface Icy Surface
Chevrolet Pickup Vehicle Type
Figure 8. The same was true for starting traction. especially for braking on both packed snow and ice. while all-season tires showed the worst performance. Tests showed that lightweight (aluminum) studs produced better stopping and starting traction results on snow and ice than standard studded tires and Blizzaks.
3. such as yaw instability. Tests of stopping and starting traction performance for different vehicle types and configurations on snow and ice showed that significant differences occur for braking distances. 4. and suspension dynamics. tire size and contact area. 7. Stopping and starting traction performance on snow and ice generally diminishes at temperatures below about 20 degrees F (-7 degrees C). rear-wheel drive).
. However. and were not likely related to the drive configuration (front-wheel drive. other controllability penalties. Wear on lightweight-studded tires diminishes their stopping and starting traction performance capability. This effect was most prominent for braking maneuvers. The use of only two studded tires (on only the front wheels) produced stopping traction results on snow and ice that were about halfway in between the results of four studded tires and four all-season tires. 5. Studded tires produce their best traction on snow or ice near the freezing mark and lose proportionately more of their tractive ability at lower temperatures than do studless or all-season tires. These differences were primarily ascribed to vehicle differences such as weight distribution. Lateral traction performance differences between the various tire groups did not show significant variation. where worn tires with lightweight studs had stopping distances on snow that were 12 percent longer than when new. 6. should be considered. but not for starting traction. The Caprice stopped 15 percent shorter than the pickup truck and 26 percent shorter than the Lumina.
and were shortest for studded tires followed by the Blizzaks (8 percent longer) and all-season tires (15 percent longer). involved the use of the same three types of vehicles used in the 1995 tests (Lu 1995).1) 83. Stopping distances were recorded from initial vehicle speeds of 25 mph (40.9 (21.7) 128.0 (5.6 (39.9 (19.6) 116.3 (19.3 (19.3 (19.4 (24. Stopping Distances (ft (m)) for 25 mph (40.7 (5.9 (38.7 (5.9 (25. 1995).0) 17. and bare pavement.4 (5.9 (46. and Bare Pavement.6 (39.5) 59.0) 17.6) 126.1)
.6) 63.3 (19. conducted by the University of Alaska at Fairbanks. stopping distances were generally two or three times longer than on packed snow. Table 16.0) Caprice 50. than the studded tires.6) 63.4) 105. Most tests were conducted at near-freezing temperatures. 1995)
Packed Snow Surface Blizzaks Studded All Season Icy Surface Blizzaks Studded All Season Bare Pavement Blizzaks Studded All Season Lumina 62.2) 68.4 (36.5) Pickup 79. Results (Table 16 and Figure 9) showed that all three tire types produced the same results on packed snow.7) 122.4 (5.2) 16.2) 152.0) 64.0 (31.1)
16. The first test. tests were conducted to determine the performance of studded tires in comparison with all-season tires and Blizzak tires on packed snow. On ice.5) 117.8 (15.6 (19. the Lumina had four-wheel ABS.1) 57.8 (35.9) 68. but the differences were deemed insignificant.0 (37.9) 106. Fairbanks (based on Lu et al.3 km/h) on Packed Snow. On bare pavement. and bare pavement.2)
16.5) Average 64.OTHER PERFORMANCE DATA FROM ALASKA In another study performed in Alaska (Lu et al. stopping distances for the Blizzaks and all-season tires were 5 percent and 2 percent shorter.2) 128.3 km/h) at a location in Fairbanks on packed snow.4 (18. but for this series of tests. respectively.4 (17.6 (20.0 (5. Ice.2) 118. ice.6 (32.2) 16. ice.4)
104.3 (32.5 (35.6) 64.
45 40 Stopping Distance (m) 35 30 25 20 15 10 5 0 Packed Snow Surface Icy Surface Surface Type Bare Pavement Blizzaks Studded All Season
Figure 9. the all-season tires were not tested. Results showed that on packed snow. conducted by the University of Alaska at Anchorage (Lu et al. Stopping Distances (m) for Various Tires on Slippery and Bare Pavement. stopping distances were determined for packed snow. ice. 1995) In a similar test. and bare pavement. Fairbanks (Lu et al. except that a Ford Crown Victoria (rear-wheel drive with ABS) was exchanged for the Caprice. On bare pavement. respectively. The vehicles were the same. 1995). the studded tires had stopping distances 40 percent and 42 percent longer than the Blizzaks and all-season tires. the Blizzaks and studded tires were nearly equivalent and both were significantly better than the all-season tires (Table 17 and Figure 10). On the icy surface.
. but the studded tires stopped 11 percent shorter than the Blizzaks.
Table 17. Stopping Distances (ft (m)) for 25 mph (40.3 km/h) on Packed Snow, Ice, and Bare Pavement, Anchorage (based on Lu et al. 1995)
Packed Snow Surface Blizzaks Studded All Season Icy Surface Blizzaks Studded All Season Bare Pavement Blizzaks Studded All Season Lumina Pickup Crown Victoria 50.5 (15.4) 39.8 (10.6) 37.1 (11.3) 52.8 (16.1) 36.1 (11.0) 36.7 (11.2) 55.4 (16.9) 53.1 (16.2) 47.6 (14.5) Average 40.7 (12.4) 41.9 (12.8) 51.8 (15.8)
97.1 (29.6) 66.6 (20.3) 64.3 (19.6) 83.7 (25.5) N/A N/A
100.1 (30.5) 87.9 (26.8) 86.6 (26.4) 78.1 (23.8) N/A N/A
11.1 (3.4) 17.4 (5.3) 10.8 (3.3)
30 25 Stopping Distance (m) 20 15 10 5 0 Packed Snow Surface Icy Surface Surface Type Bare Pavement Blizzaks Studded All Season
Figure 10. Stopping Distances (m) for Various Tires on Slippery and Bare Pavement, Anchorage (Lu et al. 1995) Tests of starting traction times conducted in Fairbanks and Anchorage (Lu et al. 1995) showed that on bare pavement, studded tires fared the worst (or tied for worst) 38
when compared with the other tires. In Fairbanks, the test involved use of the Chevrolet pickup accelerating to 25 mph (40.3 km/hr). The Blizzaks gave the best starts, with times 7 percent faster than the studded and all-season tires, which had the same starting traction performance. In Anchorage, the Crown Victoria was used for the same test. In this case, the Blizzaks and all-season tires had essentially the same starting traction, and showed about 10 percent lower elapsed time to reach the target speed. In research performed much earlier in the State of Alaska (Alaska Studded Tire Study 1973), the merits of studded tires were debated from the standpoint of performance and safety. This study reported on performance tests conducted by the Canadian Safety Council in 1971 that examined stopping distances, traction, and maneuverability on ice, snow, wet and dry asphalt, and wet and dry concrete. Though some of the results may not apply to tire and automotive technology that has since advanced 30 years, some observations are still meaningful. The 1973 Alaska study documented that during stopping distance tests, studded tires lose their effectiveness with declining temperature, and their performance becomes essentially indistinguishable from ordinary highway tires below 0 degrees F (-18 degrees C) (Figure 11). The effect of sand on ice also becomes minimal. This is consistent with other sources that suggest the colder and harder the ice, the less effective studs become. The 1973 Alaska report also stated that there was almost no difference in stopping distances on wet or dry asphalt between vehicles equipped with highway tires, two studded tires on the rear, or four studded tires. For concrete, though, studded tires required longer stopping distances than highway tires. On dry pavement, a vehicle equipped with two studded tires required 11 percent longer distances to stop and 16 39
Stopping Distance – Feet x 100
Temperature, Deg F. Figure 11. The Effect of Temperature (F) on Traction for Studded and Non-studded Tires (Alaska Studded Tire Study, Phase III, 1973) percent longer when the concrete was wet. For four studded tires, this difference increased to 16 percent for dry conditions and 32 percent for wet conditions. Though such statistics may not be entirely valid for today’s CP studs, radial tires, and ABS, they still indicate a trend that is likely to be valid: studded tires on wet or dry concrete provide less traction than non-studded tires. This is likely because the studs cannot penetrate the harder roadway surface, which actually lowers the effective coefficient of friction, in much the same way as studded tires lose effectiveness on ice at lower temperatures.
4. WINTER TIRE SAFETY
Aside from pure traction issues, a number of varied and complex safety issues surround the use of studded and non-studded tires. Some of the effects of studded tires are beneficial, and some are not; some seem obvious while others are subtle. Although not the primary focus of this report, a number of these issues are presented here briefly, including the effect of studded tires on accident risk driving hazards caused by pavement wear incidental traction improvements on roadways “roughened” by studded tire use the effect of studded tires on driver behavior. THE EFFECTS OF STUDDED TIRE USE ON TRAFFIC ACCIDENT RISK An extensive analysis of accident rates for vehicles equipped with studded tires was undertaken in Norway in 1998 (Elvik 1998). This “meta-analysis” involved a statistical analysis of 11 previously published studies on this topic from researchers in the U.S., Canada, Scandinavia, Germany, and Japan. The 11 studies showed large variations in results: the effects of studded tires on accident rates on snow- or ice-covered roads ranged from a reduction of 72 percent to a reduction of 4 percent. All of the studies showed a benefit from studded tires, though the effect was not significant in all the studies. On bare roads, the effects of studded tires on accident rates varied even more widely: from a 68 percent decline to a 151 percent increase. For all road surfaces combined, the effects of studded tires on automobile accident rates ranged from a 10 percent increase to a 70 percent decline. 41
which is not likely to be accurate anymore. studless winter tires. Early data (from the 1970s) often suggested much greater reduction in accident rates for users of studded tires (on the order of 40 to 70 percent). It was concluded that the use of studded tires improves road safety by reducing the accident rate. regardless of what tire they were using.The Norwegian study statistically analyzed the results of these 11 studies and classified them by strength. drivers using non-studded tires reportedly cancelled more trips and drove more cautiously than those with studded tires. Other confounding factors may have skewed historical and more recent accident rate predictions. Accident rate declines for vehicles equipped with studded tires that were presented in the 1970s have been postulated to have been wrong because of “selective recruitment” of the drivers (Elvik 1998). they may have been purchased by “safer drivers” who were more concerned about safety and hence likely to have a lower accident rate. The gap has narrowed both because regulations around the world have limited the aggressiveness of the studs and because tire technology has improved the frictional characteristics of newer. First. The study found no significant difference in accident involvement 42
. Hence. A separate Norwegian study sent a questionnaire to drivers who reported car damage during the winter of 1994/1995 to assess the effect of studded tires on winter accident rates. This disparity is caused by several factors. Also. but the effect is quite small. on the order of 1 to 10 percent. Some of these driver behavioral factors will be discussed in a later section. the difference in friction between studded tires and non-studded winter tires is likely to have become smaller over time. the true safety benefits of studded tires have been reduced relative to non-studded tires. When studded tires were newly available.
studded tire usage rates were close to 100 percent. A 1993 ban of studded tires in Japan resulted in “extremely slippery” roads. rutting allows standing water to accumulate in wheel troughs. smoother pavement. by extensive use of studded tires may have an overall benefit to the traction (and hence safety) of the roadway. First. a higher numbers of accidents. Standing water in ruts can also cause excessive road spray to obscure the vision of nearby motorists. and a 20-fold increase in the amount of anti-freezing agents applied (Asano et al. 2001). thereby raising the potential for hydroplaning. Non-studded tires tend to pack the snow into compact ice.between drivers with studded and non-studded tires when controlling for other car and driver characteristics (Fosser 1995). rutting can cause “tramlining. When water is present.” which adversely affects the directional controllability of a car by “steering” the car toward the center of the rut. or by upsetting the lateral stability while the car changes lanes (from rut to rut). Increased wear from studded tire use can also cause premature loss of pavement paint striping and marking. In the mid-1980s in Hokkaido. DRIVING HAZARDS CAUSED BY PAVEMENT WEAR Several obvious and well-understood driving hazards result from pavement rutting caused by accelerated wear that is the result of studded tire use. either pavement or ice. INCIDENTAL TRACTION IMPROVEMENTS Some studies have suggested that the roughening of driving surfaces. which can cause complete lack of control. as
. while studded tires tend to wear down this surface fairly quickly (Fridstrom 2001). During the period from 1989 to 1993.
Hence. Another study concluded that a ban on studded tires resulted in a slight decrease in fatal and injury-only accidents but in an increase in skidding accidents (Minsk and Kajiya 1993). Icy or snowy roads were postulated to have been moderately roughened through use of studded tires. Another 44
. an unintended consequence of less pavement wear was lower skid resistance. which made it safer for all vehicles. including those with non-studded tires that used the same roads. the risk would increase by 17 percent. slippery roads did not become a problem until 1992 when the studded tire use rate fell below 20 percent. A 1998 study in Sweden investigated diminished skid resistance on roadways caused by the advent of lighweight studs and wear-resistant pavement mixes (Hobeda 1998). The increase in risk was found not to be linearly dependent on the proportion of cars equipped with studded tires because even a small proportion of cars with studded tires is sufficient to roughen icy roads.studded tires were phased out. 95 percent of the vehicles in Finland are equipped with studded tires (Kallberg 1995). Another Finnish study by the same author concluded that one of the positive aspects of studded tire use is that it provides better traction on pavements that are susceptible to wear by studded tires (Kallberg 1993). If only 20 percent of the vehicles had studded tires. Before these developments. According to a 1995 study. The study concluded that the overall accident risk in winter would increase by only 9 percent if only 50 percent of the vehicles were equipped with studded tires. studded tire use in the winter months tended to roughen pavement texture and thus improve skid resistance in the summer. thereby improving traction for all vehicles whether or not they are equipped with studs.
. DRIVER BEHAVIOR Human behavior should not be overlooked in assessing the safety of studded tires.” wherein drivers of vehicles fitted with studded tires on fair days who encountered unexpected slippery conditions might have a traction advantage. One body of research on the use of studded tires in Norway concluded that a reduction in the use of studded tires would not lead to a significant increase in injury accidents. The researchers found that during severe winter conditions. Another study found the risk for drivers of vehicles with studded and non-studded tires to be equal (Fosser 1996). It has been shown that even a small increase in speed can negate any increase in traction performance of studded tires. and that such drivers had not lost this advantage by adapting (upward) their speed relative to drivers of vehicles without studded tires. thereby improving grip for vehicles both with and without studded tires (Oberg 1994).Swedish study indicated that pavement roughening by studded tires improves wet friction traction on bare surfaces. though there is not consensus about the effects. drivers of vehicles with studded tires tended to drive faster than others. They postulated that this was because of a “surprise factor. their analysis also found that accident risk was reduced on days when there was no snow on the ground or in the air. Perhaps oddly. Yet another study concluded that drivers of vehicles with studded tires drive more safely than those with non-studded tires (Sigthorsson 1998). Some studies have shown that drivers using studded tires tend to be more confident and therefore tend to drive faster than those using non-studded tires (Fridstrom 2001. creating a greater likelihood of control loss (Fridstrom 2001). Kallberg et al. hence increasing risk. 1995).
Cost of Studded versus Studless Tires An informal survey of tire costs in the Seattle area revealed that typical winter tires for a mid-sized car vary substantially in cost.000 to 40. in Washington. OTHER FACTORS AFFECTING THE USE OF STUDDED TIRES Other factors to be considered in the debate over the use of studded tires include such issues as the cost of studded tires in comparison with new studless winter tires the increase in fuel consumption for studded versus studless tires convenience and mobility. negotiated steep curves more carefully. The same size Blizzak tire costs closer to $100. Drivers who had previously been using studded tires did not want to switch back to using studded tires (Roine. drove at lower speeds. After its useful life as a snow tire. 1994). cannot be driven on the street in the summer months. However. The studded snow tire. and expressed complete satisfaction with the studless tires. its studs can be removed. the Blizzak can easily (and legally) be “used up” during non-winter months. and it can be used as a highway tire. For example. a typical 205/60-14 studded snow tire costs approximately $60 (equipped with studs).A study from Finland also examined driver behavior.
. Each tire is designed to give three or four average winter seasons before losing effectiveness as a winter tire.000 miles. including the trade-off in the use of traditional snow-clearing methods the introduction of suspended particulate matter (dust) from roadway wear increased noise from studded tires. the Blizzak is designed to operate at its best for 30. The researchers found that drivers using studless tires braked more softly.
7 percent. dry.4 to 0. The use of studded tires affords users (at least) the perception of convenient icy-weather traction without the inconvenience associated with either staying home or using temporary traction aids such as chains.Fuel Consumption Field measurements conducted in Finland showed that slippery. ice.3) increased fuel consumption by 0. Given data presented from the Alaska studies (Lu 1994. for most circumstances. 1995).1 (from 0. and uneven roadway surfaces can increase fuel consumption by 15 percent over bare. relative effects on fuel consumption of snow. fuel consumption for studded tireswill likely be higher. However. For some states. and road surface unevenness far outweigh the effects of studs on tires. A decrease in coefficient of friction of 0. Hence. The difference in fuel consumption between bare pavement and the most slippery icy road was 4 percent. than that of studless tires. Fuel consumption with studded tires was about 1. the fuel consumption of studded versus studless tires depends on which tire creates the best traction. including winter highway snow and ice control. The tangible and intangible costs and benefits of studded tires and other traction-enhancing options must be compared with alternative methods of gaining mobility. Convenience and Mobility There is an intangible value of the mobility gained from the opportunity to use vehicles on roadways regardless of the weather. and even surfaces (Anila 1994). have better traction than studded tires. 47
. winter highway maintenance comprises a large part of the yearly budget. which showed that studless tires.2 percent higher than that with studless winter tires. on the average. snowy. which is a function of the roadway condition.
Noise levels for pavement-tire contact are also affected by the roughness of the pavement surface (which. Tests from the early 1970s showed that the increase in noise from studded tires (as compared with non-studded tires) was most prominent at speeds of 20 mph (32
. 2001). Japan. Suspended Particulate Matter While pavement damage and subsequent increases in hydroplaning and road spray have been well documented. NCHRP 1975). Several studies performed in Japan documented the significantly increased presence of this dust during periods of stud usage (Fukuzaki 1985 and Asano 2001). where studded tire use was banned in 1990.In Hokkaido. In addition to increased ambient noise levels from these effects. the roadway maintenance costs increased sharply throughout the 1990s. In fact. causing passenger discomfort and an increased rate of vehicle deterioration. pavement roughness can transmit vibration to the vehicle chassis. in turn. the use of deicing agents had increased by 20 times and abrasives had increased 30 times the amount applied in 1991-1992 (Asano et al. By the winter of 1998-1999. the increase in suspended particulate matter (SPM) or dust from stud use is a more complicated safety issue. concerns about air pollution from airborne dust resulted in a national ban on studded tires in Japan in the early 1990s. Mechanical interaction between the stud and pavement releases particulate matter (airborne dust) that is considered a risk to human health. can be roughened by the use of studs). Noise Further studies have documented the increase in noise from vehicles equipped with studded tires (Fridstrom 2001.
. For noise increases on roughened pavement compared with adjacent (smoother) pavement. at higher speeds of 60 mph (96 km/h). the differences diminished somewhat (NCHRP 1975).km/h). the differences were most pronounced when measured inside the vehicle.
such as the Blizzak. The traction of studded tires is slightly superior to studless tires only under an ever-narrowing set of circumstances. Traction performance can be characterized in many ways. For those conditions in which studded tires provided better traction than studless tires. cornering. Though all factors
. controllability. For the majority of test results reviewed for snow. including braking. studded tires performed as well as or worse than the Blizzak tire. the increment usually was small. and with the advent of the new “studless” tire. Studded tires produce their best traction on snow or ice near the freezing mark and lose proportionately more of their tractive ability at lower temperatures than do studless or all-season tires. since the early 1990s. where they have been shown to provide up to 100 percent gain in certain tests. 3. The maximum frictional gain (in comparison to non-studded (not studless) tires) is found for new studded tires on smooth ice. the traction benefit for studded tires is primarily evident on clear ice near the freezing mark. The precise environmental conditions under which studded tires provide a traction benefit are relatively rare. and grade climbing. 2. or if the comparison is made with studless tires. With less aggressive (lightweight) studs being mandated. However.CONCLUSIONS
1. a condition whose occurrence is limited. acceleration. 4. the relative frictional gain of studded tires diminishes or becomes negative on roughened ice. and for ice at lower temperatures. as the studs wear. as the temperature drops.
the single best indicator of tire performance is braking distance and deceleration. especially for braking on both packed snow and ice. which in turn were 8 percent shorter than for all-season tires. in comparison to studded tires (which were second) and all-season tires (which were last). should be considered.are important. However. other controllability penalties. such as yaw instability. In another set of tests in Alaska. for asphalt. there is little difference in stopping distance between studded and non-studded tires. In one set of stopping distance tests in Alaska. and allseason tires performed nearly equally on snow. This is especially true for concrete. 8. studless Blizzak tires offered the best traction performance. in comparison to non-studded tires. studless. studded tires tend to have poorer traction performance than other tire types. 5. On bare pavement. stopping distances for studded tires were 15 percent shorter than for Blizzaks. 6. studded. On ice. The use of two studded tires on the front of a vehicle produced stopping traction results on snow and ice that were about halfway between the result of four studded tires and four all-season tires. when averaged across several vehicles. Studded tires reduce the difference in friction factor between optimum-slip and locked-wheel braking. 7. This may reduce the risk of drivers misjudging the necessary braking distance and may improve the braking potential for anti-lock brakes.
Studded tires may lose more of their tractive ability over time (from stud wear) than studless tires.039 to 0. Tractive performance of studded tires is sensitive to stud wear. Studded tires increase fuel consumption by a small amount (~1.043 in. and premature damage to pavement markings. A Norwegian study concluded that the use of studded tires tends to reduce the accident rate by a small amount—from 1 to 10 percent.0-1. 13. 15. 11. 12.024 in. the frictional effect from the studs becomes negligible.10. 16. 52
. (1. The roughening of ice and pavement from studded tires provides a safety benefit for all vehicles (with and without studs) by helping to prevent formation of smooth. hence they drive more safely. hydroplaning on accumulated water in the ruts.2 percent) over non-studded tires on bare roadways. There is not consensus on these points: 1) drivers with studded tires care more about safety. (0. 2) they drive faster (because of a false sense of security or confidence). excessive road spray. A number of driver behavior issues have been postulated to affect the judgment of studded tire effectiveness. glare ice. But the other effects of unevenness.1 mm). When stud protrusion diminishes to 0. Pavement rutting caused by accelerated wear from studded tires can cause the dangerous conditions of tramlining. and 3) drivers with non-studded tires avoid driving when weather is severe. 14. Tire tread wear (on studded tires) has relatively little frictional effect if stud protrusion is maintained at 0. The cost of studless tires is significantly higher than studded tires—by approximately 50 percent.6 mm).
Suspended particulate matter from pavement dust created by studded tires and noise from studded tires are health concerns in heavily traveled urban areas. and ice are far more significant than this factor and can increased fuel consumption by 15 percent.snow.
F. Elvik.S.” Pennsylvania Transportation Institute. Fridstrom. 1998. Yanaka.
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“Winter Driving – Studded Tires. David. L. Vol. Olle. Samuelsson. “ FinnRA Reports 87/1993. 51. D. 3. Seattle. “Road Grip of Winter Tyres. Finland. Wash.” Transportation Research Record.wsdot. Simanaitis.” http://www. and Jian J. and Y. 2001. Washington State Department of Transportation.. Washington. Helsinki. Nordic Road and Transport Research.gov/traveler/wintertravel/studtire. Lutfi. December 1999. 10. of the OECD Workshop on Road Winter Maintenance. Mikko. Minsk. D. 1998. 1994. “Effects of Studded Tires. M.” Proceedings of the ASCE 3rd International Conference on Applications of Advanced Technologies in Transportation Engineering.” Nordic Road and Transport Research. “Driver Behaviour on Sharp Curves and Queues on Main Roads.” Transportation Research Board. October 1820.wa. Praha. “Traction Performance of Transit and Paratransit Vehicles in Winter. Gudrun. 1975. Sigthorsson. Haraldur... “Snow and Ice Control in Japan and United States. National Research Council.C. Sweden. Washington. 2. No.” Swedish Road and Traffic Institute. 1731. No.” Nordic Road and Transport Research. 2000.” Proceedings.Malmivuo. Issue 4. 1991. No. No. Nordstrom.htm
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tipped with tungsten carbide. Order 6902. § 204-24-030. (2) Metal studs shall be inserted only in a new tire or a newly-recapped tire which has molded in the tread the "pin-holes" into which metal studs are to be inserted. (5) A tire shall contain a minimum of fifty-six metal studs at all times in order to qualify as a "studded tire" or as an approved traction device where traffic control signs marked "approved traction tires required" are posted. School buses and fire department equipment tires are exempt from subsection (6) of this section. Standards for Studded Tires: Studded tires shall meet the following specifications: (1) Studs shall be metal. effective 3/12/92. Statutory Authority: RCW 46. (4) When a tire is sold or offered for sale as a studded tire or when studs are installed in a new tire or a newly-recapped tire. 83-21080 (Order 83-10-01). there shall be a minimum of seventy metal studs evenly spaced around the tread of the tire.]
. filed 10/19/83. 92-05-016. filed 7/10/00. (3) Metal studs may be installed only by the tire manufacturer.330. effective 8/10/00. § 204-24-030. filed 9/14/76. § 204-24-030. § 204-24-030. Studs shall not be inserted in any new tire or newly-recapped tire after it has been driven on a vehicle. 00-15-009. (6) (7) Metal studs shall not be installed in any tire of a vehicle which has a gross vehicle weight of ten thousand pounds or over.
[Statutory Authority: RCW 46. Order 7607.420. or by a tire dealer or tire jobber who shall install the metal studs in conformance with the manufacturer's specifications. filed 2/17/70.12. § 204-24-030. filed 2/10/92.APPENDIX A State of Washington Laws Regarding Studded Tires
WAC 204-24-030.37.
As used in this title.]
Proposed State of Washington Laws Proposal is currently still being debated at the committee level (Staff: Jennifer Ziegler 786-7316). Lightweight Stud: "Lightweight stud" means a stud intended for installation and use in a vehicle tire. SENATE BILL REPORT SB 5747 SENATE COMMITTEE ON TRANSPORTATION Background: The Legislature and the Governor formed the Blue Ribbon
Commission on Transportation in 1998 to assess the local.04. make the system more accountable and predictable.
[1999 c 219 § 1.0 grams if the stud conforms to TSMI stud size 17 or larger. and prepare a 20-year plan for funding and A-2
. this means a stud that is recommended by the manufacturer of the tire for the type and size of the tire and that: (1) Weighs no more than 1.3 grams if the stud conforms to TSMI stud size 15 or 16.5 grams if the stud conforms to Tire Stud Manufacturing Institute (TSMI) stud size 14 or less. ensure that current and future money is spent wisely.272. or (3) Weighs no more than 3. A lightweight stud may contain any materials necessary to achieve the lighter weight.RCW 46. and state transportation system. (2) Weighs no more than 2. regional.
. and the general public. lightweight studs will be the only studs on the road. Fiscal Note: Requested on February 1. environmental interests. shipping. 2001. retailers may only install lightweight studs on tires. trucking. tribes. The Washington State Department of Transportation projects that by July 2005.investing in the transportation system. Starting July 1. The commission consisted of 46 members representing business. Effective Date: The bill contains an emergency clause and takes effect on July 1. Recommendation Five outlined several ways to invest in maintenance. labor. 2001. transit. 2001 (bill has not yet passed). Appropriation: None. Summary of Bill: Beginning July 1. The buyer of the tires must pay the fee to the seller of the tires and the seller must send the fees to the Department of Revenue. The commission made eighteen recommendations to the Governor and the Legislature. and improvement of the entire transportation system so that transportation benchmarks can be achieved. In 1999. The commission concluded that one method for preserving the transportation system was to phase out studded tires or establish a surcharge to recognize the cost of studded tire damage to the roadways. agriculture. a fee of $15 per tire is levied on the sale of each studded tire. ports. government. preservation. rail. the Legislature enacted a bill requiring wholesalers to only sell lightweight studs for tires. 2001. The fees must be deposited in the motor vehicle fund.
-.WASHINGTON STATE LEGISLATURE History of HB 1670 HB 1670 Sponsors: By Request: Imposing a fee on studded tires. Representatives Fisher.2001 1ST SPECIAL SESSION Apr 25 By resolution.
. Poulsen The Blue Ribbon Commission on Transportation
Companion Bill(s): SB 5747 -. Ruderman. reintroduced and retained in present status. Mitchell. reintroduced and retained in present status.2002 REGULAR SESSION -Jan 14 By resolution. referred to Transportation. -.2001 REGULAR SESSION -Jan 31 First reading.
Permitted: October 1-May 1 Permitted: November 1-April 1 Permitted: November 1-April 15 Permitted: No restrictions. Sept. Not permitted. automobiles with out-of-state registrations (only if automobile is in the course of passing through the state for a period of not more than 30 days). Permitted: October 1-April 15 Not permitted. Not permitted except for snow and ice driving conditions Not permitted.
. Metal illegal.APPENDIX B Other Studded Tire Regulations
STATE STUDDED TIRE REGULATIONS
Alabama Alaska Arizona Arkansas California Colorado Connecticut Delaware District of Columbia Florida Georgia Hawaii Idaho Illinois Indiana Iowa Kansas Kentucky Louisiana Maine Maryland Massachusetts Michigan Minnesota Mississippi Missouri Montana Nebraska Nevada New Hampshire New Jersey New Mexico New York North Carolina North Dakota Ohio Oklahoma Oregon Pennsylvania Rhode Island South Carolina South Dakota Tennessee Texas Utah Vermont Virginia Washington West Virginia Wisconsin Wyoming Rubber studs permitted. Permitted: November 1-April 15 Permitted: November 1-April 1 Permitted: November 1-April 1 unless specified differently by Department of Transportation because of weather conditions. Permitted: Sept. School buses and municipal fire vehicles permitted to use studs anytime. Not permitted except under certain conditions. Permitted: No restrictions. Permitted: October 1-May 1 Permitted: November 15-April 15 Permitted: November 1-April 30 Permitted: Year Round Permitted: November 15-April 30 inclusive Permitted: October 15-April 15 Permitted: October 15-April 15 Not Permitted. Not permitted except for nonresidents who are subject to certain restrictions. Permitted: October 1-April 15 Not permitted. 1-March 31 Permitted: November 2-April 30 unless otherwise authorized by registrar. Permitted: November 1-March 31 Permitted: October 1-May 31 Permitted: November 1-April 1 Permitted: October 1-April 30 Permitted: No restrictions Permitted: November 15-April 1 No regulations. Studs which do not damage highway are permitted. Also school buses from November 15-April 1. Permitted: October 15-March 31 Permitted: No restrictions Permitted: October 15-April 15 Permitted: November 1-April 1 Permitted: November 1-April 15 Not permitted except for authorized emergency vehicles. Only studs that will not damage the highway are permissible. Not permitted. 30-April 15 south of 60 degrees N. Exception: school buses may use studded tires any time during the year. Check local officials. Permitted: October 1-May 1 Not permitted except in western counties: Nov. 15 — May 1 north of 60 degrees N. Rural mail carriers may use studded tires under certain conditions. vehicles used to deliver mail. Chains required in snow emergencies. Permitted: October 1-April 30. Permitted: November 1-April 15 Permitted: November 15-April 1 Permitted if not projected more than 1/16-inch when compressed. Permitted: October 16-April 30 Permitted: No restrictions Permitted: October 15-April 15. Full time nonresident students and nonresidents employed within Minnesota are not permitted use of studded tires regardless of vehicle registry.
Figure B-1. Maryland—Exception: western counties Nov. 1-March 31 Michigan—Exception: certain conditions. Wisconsin—Exceptions: authorized emergency vehicles. school buses from Nov. Texas—Studs that will not damage the highway are permissible. who are subject to certain restrictions.Exceptions Florida—Studs that do not damage the highway are permitted Georgia—Exception: snow and ice driving conditions. rural mail carriers under certain conditions. States in Which Studded Tire Use Is Not Permitted
INTERNATIONAL REGULATIONS ON USE OF STUDDED TIRES (LU 1994) Canada Ontario Quebec Nova Scotia Newfoundland New Brunswick Prince Edward Island British Columbia Manitoba Saskatchewan Germany Sweden Finland Japan Prohibited Permitted October 15-April 15 Permitted October 15-April 15 Permitted November 1-April 30 Permitted October 16-April 14 Permitted October 1-May 31 Permitted October 1-April 30 Permitted October 1-April 30 No Restriction Prohibited October 31-Easter November 1-March 31 Prohibited
. 15-April 1. vehicles used to deliver mail. Minnesota—Exceptions: nonresidents. vehicles with out-of-state registrations.
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