ASTM F1649-20

Standard Test Methods for Evaluating Wet Braking Traction Performance of Passenger Car Tires on Vehicles Equipped with Anti-Lock Braking Systems

SIGNIFICANCE AND USE
5.1 Braking traction is an important factor in vehicle control especially on wet pavements. These test methods permit an evaluation of tires for their relative or comparative performance on an ABS-equipped vehicle. See Annex A1 for background information for interpretation of results and meaningful evaluation of tire design features for their influence on wet traction performance.  
5.2 Although stopping distance is important for vehicle control, the ability to steer the vehicle on a selected trajectory is equally or, in some instances, more important. The wet traction capability of tires influences both of these measured parameters since the tires are the link between the ABS and the pavement and provide the traction or tire adhesion level that permits the ABS to function as intended.  
5.3 The absolute values of the parameters obtained with these test methods are highly dependent upon the characteristics of the vehicle, the design features of the ABS, the selected test pavement(s), and the environmental and test conditions (for example, ambient temperature, water depths, test speeds) at the test course. A change in any of these factors may change the absolute parameter values and may also change the relative rating of tires so tested.  
5.4 These test methods are suitable for research and development purposes where tire sets are compared during a brief testing time period. They may not be suitable for regulatory or specification acceptance purposes because the values obtained may not necessarily agree or correlate, either in rank order or absolute value, with those obtained under other conditions (for example, different locations or different seasonal time periods on the same test course).
SCOPE
1.1 These test methods cover the measurement of two types of ABS vehicle behavior that reflect differences in tire wet traction performance when the vehicle is fitted with a series of different tire sets to be evaluated.  
1.1.1 The stopping distance from some selected speed at which the brakes are applied.  
1.1.2 The lack of control of the vehicle during the braking maneuver. Uncontrollability occurs when the vehicle does not follow the intended trajectory during the period of brake application despite a conscious effort on the part of a skilled driver to maintain trajectory control. Uncontrollability is measured by a series of parameters related to this deviation from the intended trajectory and the motions that the vehicle makes during the stopping maneuver.  
1.1.3 Although anti-lock braking systems maintain wheel rotation and allow for a high degree of trajectory control, different sets of tires with variations in construction, tread pattern, and tread compound may influence the degree of trajectory control in addition to stopping distance. Thus vehicle uncontrollability is an important evaluation parameter for tire wet traction performance.  
1.2 These test methods specify that the wet braking traction tests be conducted on two specially prepared test courses: (1) a straight-line (rectilinear) “split-µ” (µ = friction coefficient) test course, with two test lanes deployed along the test course (as traveled by the test vehicle); the two lanes have substantially different friction levels such that the left pair of wheels travels on one surface while the right pair of wheels travels on the other surface; and (2) a curved trajectory constant path radius course with uniform pavement for both wheel lanes.  
1.3 As with all traction testing where vehicle uncontrollability is a likely outcome, sufficient precautions shall be taken to protect the driver, the vehicle, and the test site facilities from damage due to vehicle traction breakaway during testing. Standard precautions are roll-bars, secure mounting of all internal instrumentation, driver helmet, and secure seat belt harness, etc.  
1.4 The values stated in SI units are to be regarded as the standard. The values given in parenthesis a...

General Information

• Status: Published
• Publication Date: 30-Sep-2020
• ICS: 43.040.40 - Braking systems
• ICS: 83.160.10 - Road vehicle tyres
• Technical Committee: F09 - Tires
• Drafting Committee: F09.20 - Vehicular Testing

Relations

• Refers: ASTM E1136-19 - Standard Specification for P195/75R14 Radial Standard Reference Test Tire
• Effective Date: 01-Oct-2019
• Refers: ASTM F1805-18 - Standard Test Method for Single Wheel Driving Traction in a Straight Line on Snow- and Ice-Covered Surfaces
• Effective Date: 01-Nov-2018
• Refers: ASTM F2493-18 - Standard Specification for P225/60R16 97S Radial Standard Reference Test Tire
• Effective Date: 01-Jan-2018
• Refers: ASTM E1136-17 - Standard Specification for P195/75R14 Radial Standard Reference Test Tire
• Effective Date: 01-Oct-2017
• Refers: ASTM F457-04(2017) - Standard Test Method for Speed and Distance Calibration of Fifth Wheel Equipped With Either Analog or Digital Instrumentation
• Effective Date: 01-May-2017
• Refers: ASTM F1805-16 - Standard Test Method for Single Wheel Driving Traction in a Straight Line on Snow- and Ice-Covered Surfaces
• Effective Date: 01-Jan-2016
• Refers: ASTM E1136-14 - Standard Specification for P195/75R14 Radial Standard Reference Test Tire
• Effective Date: 15-Aug-2014
• Refers: ASTM F2493-14 - Standard Specification for P225/60R16 97S Radial Standard Reference Test Tire
• Effective Date: 01-Jun-2014
• Refers: ASTM F1650-98(2014) - Standard Practice for Evaluating Tire Traction Performance Data Under Varying Test Conditions
• Effective Date: 01-Jan-2014
• Refers: ASTM F1805-12 - Standard Test Method for Single Wheel Driving Traction in a Straight Line on Snow- and Ice-Covered Surfaces
• Effective Date: 01-Nov-2012
• Refers: ASTM F457-04(2010) - Standard Test Method for Speed and Distance Calibration of Fifth Wheel Equipped With Either Analog or Digital Instrumentation
• Effective Date: 01-Feb-2010
• Refers: ASTM F538-09 - Standard Terminology Relating to the Characteristics and Performance of Tires
• Effective Date: 15-Jun-2009
• Refers: ASTM F1046-01(2008) - Standard Guide for Preparing Artificially Worn Passenger and Light Truck Tires for Testing
• Effective Date: 01-Oct-2008
• Refers: ASTM F1572-08 - Standard Test Methods for Tire Performance Testing on Snow and Ice Surfaces
• Effective Date: 01-Oct-2008
• Refers: ASTM F2493-08 - Standard Specification for P225/60R16 97S Radial Standard Reference Test Tire
• Effective Date: 01-May-2008

Overview

ASTM F1649-20: Standard Test Methods for Evaluating Wet Braking Traction Performance of Passenger Car Tires on Vehicles Equipped with Anti-Lock Braking Systems (ABS) provides comprehensive test methods to measure the wet braking traction of passenger car tires. This standard is especially relevant for vehicles with ABS technology, ensuring that testing reflects real-world safety and performance concerns under wet pavement conditions. The standard focuses on both stopping distances and the vehicle's controllability during emergency braking maneuvers, considering the significant influence of tires on ABS function and overall vehicle control.

Key Topics

• Wet Braking Performance: The standard outlines procedures for evaluating stopping distance and vehicle control when tires are subjected to emergency braking on wet surfaces.
• ABS Vehicle Behavior: Explores how different tire sets can affect ABS-equipped vehicle stopping distances and trajectory control.
• Test Course Layout: Defines requirements for both straight-line ("split-μ") and curved-path test courses, using surfaces with different friction levels to assess tire performance under varied conditions.
• Measuring Uncontrollability: Introduces parameters to quantitatively assess any deviation from the intended vehicle trajectory during braking, such as trajectory deviation and yaw velocity.
• Comparative Tire Performance: Enables reliable comparisons between different tire models, construction types, tread designs, and rubber compounds under controlled, repeatable wet conditions.
• Instrumentation and Data Collection: Specifies the use of advanced measurement systems, including distance, speed, and yaw sensors, as well as manual and computerized data acquisition methods.
• Test Conditions and Variables: Details the influence of vehicle characteristics, ABS design, ambient temperature, water depth, and test speeds on braking results.
• Safety Precautions: Highlights the importance of driver protection measures such as roll-bars, secure harnesses, and careful course setup.

Applications

ASTM F1649-20 is highly valuable in multiple practical scenarios:

• Tire Development and R&D: Tire manufacturers use these wet traction test methods to research, design, and refine tread patterns and rubber compounds for optimal ABS performance.
• Comparative Product Evaluation: Fleet operators, automotive engineers, and tire retailers apply these methods to compare the relative safety and performance of different passenger car tires under wet braking conditions.
• Quality Control and Benchmarking: Internal quality assurance programs and benchmarking studies rely on this standard to monitor tire consistency and competitive positioning.
• ABS and Vehicle Testing: Automotive manufacturers and independent test laboratories utilize ASTM F1649 to understand how tires interact with vehicle ABS systems during emergency stops, informing safety feature development.
• Consumer Safety Communication: Results derived from these methods can be used to communicate performance advantages or limitations to consumers, supporting informed purchasing decisions.

Note: ASTM F1649-20 is intended primarily for research and developmental comparisons and may not be suitable for regulatory or specification acceptance due to sensitivity to test variables.

Related Standards

ASTM F1649-20 is closely associated with several other important standards in the field of automotive safety and tire testing, including:

• ASTM E274: Skid Resistance of Paved Surfaces Using a Full-Scale Tire
• ASTM E303: Measuring Surface Frictional Properties Using the British Pendulum Tester
• ASTM E501, E524, E1136, F2493: Specifications for Standard Reference Test Tires
• ASTM E1337: Determining Longitudinal Peak Braking Coefficient of Paved Surfaces
• ASTM F1650: Evaluating Tire Traction Performance Data Under Varying Test Conditions
• ASTM F1805, F1806, F1572: Test Methods for Tire Performance on Snow and Ice

These related standards collectively support comprehensive evaluation of tire safety and performance across a wide range of surfaces and environmental conditions, reinforcing the importance of ASTM F1649-20 in the context of modern vehicle safety engineering.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: F1649 − 20
Standard Test Methods for
Evaluating Wet Braking Traction Performance of Passenger
Car Tires on Vehicles Equipped with Anti-Lock Braking
Systems
This standard is issued under the fixed designation F1649; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
These test methods cover procedures for measuring the wet braking performance of passenger car
tires when tested on vehicles equipped with an anti-lock braking system (ABS). ABS operation is
accomplished by the use of wheel rotation rate sensors that detect impending wheel lockup and
controllable brake pressure regulators; both of these systems are connected to a control microproces-
sor. When potential lockup is detected for any wheel or pair of wheels, brake pressure is lowered to
forestall the lockup and maintain wheel rotation. This process is repeated until the vehicle comes to
a stop. The necessary lateral force to maintain vehicle control in an emergency braking situation is
only possible when wheel rotation is maintained. Although there may be differences in the braking
performance among the commercially available “vehicle-ABS” combinations, tires may be evaluated
for their relative or comparative wet braking performance with any one “vehicle-ABS-driver”
combination, by the methods as outlined in these test methods.
1. Scope pattern, and tread compound may influence the degree of
trajectorycontrolinadditiontostoppingdistance.Thusvehicle
1.1 These test methods cover the measurement of two types
uncontrollability is an important evaluation parameter for tire
of ABS vehicle behavior that reflect differences in tire wet
wet traction performance.
traction performance when the vehicle is fitted with a series of
1.2 These test methods specify that the wet braking traction
different tire sets to be evaluated.
tests be conducted on two specially prepared test courses: (1)
1.1.1 The stopping distance from some selected speed at
a straight-line (rectilinear) “split-µ” (µ = friction coefficient)
which the brakes are applied.
test course, with two test lanes deployed along the test course
1.1.2 The lack of control of the vehicle during the braking
(as traveled by the test vehicle); the two lanes have substan-
maneuver. Uncontrollability occurs when the vehicle does not
tially different friction levels such that the left pair of wheels
follow the intended trajectory during the period of brake
travels on one surface while the right pair of wheels travels on
application despite a conscious effort on the part of a skilled
the other surface; and (2) a curved trajectory constant path
driver to maintain trajectory control. Uncontrollability is mea-
radius course with uniform pavement for both wheel lanes.
sured by a series of parameters related to this deviation from
the intended trajectory and the motions that the vehicle makes
1.3 As with all traction testing where vehicle uncontrolla-
during the stopping maneuver.
bility is a likely outcome, sufficient precautions shall be taken
1.1.3 Although anti-lock braking systems maintain wheel
to protect the driver, the vehicle, and the test site facilities from
rotation and allow for a high degree of trajectory control,
damage due to vehicle traction breakaway during testing.
different sets of tires with variations in construction, tread
Standard precautions are roll-bars, secure mounting of all
internal instrumentation, driver helmet, and secure seat belt
harness, etc.
ThesetestmethodsareunderthejurisdictionofASTMCommitteeF09onTires
and is the direct responsibility of Subcommittee F09.20 on Vehicular Testing.
1.4 The values stated in SI units are to be regarded as the
Current edition approved Oct. 1, 2020. Published October 2020. Originally
standard. The values given in parenthesis are for information
approved in 1995. Last previous edition approved in 2013 as F1649 – 13. DOI:
10.1520/F1649-20. only.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F1649 − 20
1.5 This standard does not purport to address all of the 3.1.2.1 Discussion—The term “candidate object” may be
safety concerns, if any, associated with its use. It is the used in the same sense as candidate tire.
responsibility of the user of this standard to establish appro- 3.1.3 candidate tire set, n—a set of candidate tires. F538
priate safety, health, and environmental practices and deter-
3.1.4 control tire, n—a reference tire used in a specified
mine the applicability of regulatory limitations prior to use.
manner throughout a test program. F538
1.6 This international standard was developed in accor-
3.1.4.1 Discussion—Acontrol tire may be of either type and
dance with internationally recognized principles on standard-
typical tire use is the reference (control) tire in Practice F1650
ization established in the Decision on Principles for the
that provides algorithms for correcting (adjusting) test data for
Development of International Standards, Guides and Recom-
bias trend variations (see Practice F1650 and Annex A1).
mendations issued by the World Trade Organization Technical
3.1.5 reference tire, n—a special tire included in a test
Barriers to Trade (TBT) Committee.
program; the test results for this tire have significance as a base
2. Referenced Documents
value or internal benchmark. F538
2.1 ASTM Standards:
3.1.6 spinout, n—in tire testing, a type of uncontrollability
E274 Test Method for Skid Resistance of Paved Surfaces
defined by a loss of steering control due to rapid or substantial
Using a Full-Scale Tire
yaw, or both. F538
E303 Test Method for Measuring Surface Frictional Proper-
3.1.7 standard reference test tire, (SRTT), n—a tire that is
ties Using the British Pendulum Tester
used as a control tire or surface monitoring tire (for example,
E501 Specification for Standard Rib Tire for Pavement
Specification E1136 and F2493 tires). E1136, F1572, F1649,
Skid-Resistance Tests
F1650, F1805, F1806, F2493
E524 Specification for Standard Smooth Tire for Pavement
Skid-Resistance Tests 3.1.7.1 Discussion—This is a Type 1 reference tire.
E965 Test Method for Measuring Pavement Macrotexture 3.1.8 stopping distance, n—the path distance (rectilinear or
Depth Using a Volumetric Technique curved) needed to bring a vehicle to a stop from some selected
E1136 Specification for P195/75R14 Radial Standard Refer- initial brake application speed. F538
ence Test Tire
3.1.9 surface monitoring tire, n—a reference tire used to
E1337 Test Method for Determining Longitudinal Peak
evaluate changes in a test surface over a selected time period.
Braking Coefficient (PBC) of Paved Surfaces Using Stan-
F538
dard Reference Test Tire
3.1.10 test (or testing), n—a procedure performed on an
F457 Test Method for Speed and Distance Calibration of
object (or set of nominally identical objects) using specified
Fifth Wheel Equipped With Either Analog or Digital
equipment that produces data unique to the object (or set).
Instrumentation
F538
F538 Terminology Relating to the Characteristics and Per-
formance of Tires
3.1.10.1 Discussion—Test data are used to evaluate or
F1046 Guide for Preparing Artificially Worn Passenger and
model selected properties or characteristics of the object (or set
Light Truck Tires for Testing
of objects).The scope of testing depends on the decisions to be
F1572 Test Methods for Tire Performance Testing on Snow
made for any program, and sampling and replication plans (see
and Ice Surfaces
definitions below) need to be specified for a complete program
F1650 Practice for Evaluating Tire Traction Performance
description.
Data Under Varying Test Conditions
3.1.10.2 split-µ test—a wet traction or stopping distance test
F1805 Test Method for Single Wheel Driving Traction in a
conducted on a test course with substantially different wet
Straight Line on Snow- and Ice-Covered Surfaces
friction levels for the left and right tire test lanes. F538
F1806 Practice for Tire Testing Operations–Basic Concepts
3.1.10.3 test run—a single pass of a loaded tire over a given
and Terminology for Reference Tire Use
test surface. F538
F2493 Specification for P225/60R16 97S Radial Standard
3.1.10.4 traction test—in tire testing, a series of n test runs
Reference Test Tire
at a selected operational condition; a traction test is character-
3. Terminology
ized by an average value for the measured performance
parameter. F538
3.1 Definitions of Terms Specific to This Standard:
3.1.11 test tire, n—a tire used in a test. F538
3.1.1 anti-lock braking system (ABS), n—a collection of
sensing and control hardware installed on a vehicle to prevent
3.1.12 test tire set, n—one or more test tires as required by
wheel lockup during brake application. F538
the test equipment or procedure, to perform a test, thereby
3.1.2 candidate tire, n—a test tire that is part of a test producing a single test result. F538
program. F538
3.1.12.1 Discussion—The four nominally identical tires re-
quired for vehicle stopping distance testing constitute a test tire
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
set. In the discussion below where the test tire is mentioned, it
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
is assumed that test tire set may be substituted for test tire, if a
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. test tire set is required for the testing.
F1649 − 20
and with greater frequency with Method B procedures. Therefore, when
3.1.13 trajectory, n—the rectilinear or curvilinear path of a
using Method B, precautions should be exercised to avoid any possible
vehicle during a stopping maneuver; it is defined by the center
danger during testing. Testing shall begin with the lowest test velocities
of gravity and the transient angular orientation of the vehicle.
selected for any program and as higher velocities are approached,
F538
sufficient care shall be taken to avoid any danger to the driver, the vehicle,
and any on-site facilities during traction breakaway conditions.
3.1.13.1 intended trajectory—the intended or ideal path
NOTE 2—Test speeds lower than 10 km/h are not recommended due to
(rectilinear or curvilinear) to bring a vehicle to a stop, that is,
instrumentation insensitivity at this low speed.
under controlled angular orientation. F538
4.4 These test methods contain four annexes and one
3.1.13.2 orthogonal trajectory deviation—the perpendicular
appendix that give important information to assist in the
deviation or distance from the center of the vehicle to the TGL
meaningful evaluation of tire wet traction performance.
at the end of a stopping test. F538
4.4.1 Annex A1—Interpretation of Results and Tire Design
3.1.13.3 trajectory guide line (TGL)—the centerline marked
Feature Evaluation,
on the test course pavement that constitutes the intended
4.4.2 Annex A2—Techniques for Water Application and
trajectory; it is used by the driver to guide or steer the vehicle
Control,
on its intended path. F538
4.4.3 Annex A3—Selecting Path Radius and Test Speed for
Method B Testing,
3.1.14 uncontrollability, n—any deviation of the vehicle
4.4.4 Annex A4—Measuring Orthogonal Trajectory Devia-
from the intended trajectory (TGL) during or at the end of a
tion (Procedure 1), and
test, or both. F538
4.4.5 Appendix X1—List of Instrumentation Suppliers.
3.1.14.1 plowing—in tire testing, a type of uncontrollability
defined by a loss of steering control with no substantial vehicle
5. Significance and Use
yaw; the vehicle moves on a trajectory that is dictated by
5.1 Brakingtractionisanimportantfactorinvehiclecontrol
vehicle dynamics as determined by velocity, mass, and the
especially on wet pavements. These test methods permit an
available traction at each tire. F538
evaluation of tires for their relative or comparative perfor-
3.1.15 yaw, n—in a vehicle, the angular motion of a vehicle
mance on an ABS-equipped vehicle. See Annex A1 for
about its vertical axis through the center of gravity. F538
background information for interpretation of results and mean-
3.1.15.1 yaw velocity—the magnitude of the yaw (rotation ingful evaluation of tire design features for their influence on
or angular displacement); it may be measured by fore and aft,
wet traction performance.
vehicle vs. pavement, velocity sensors. F538
5.2 Although stopping distance is important for vehicle
control, the ability to steer the vehicle on a selected trajectory
4. Summary of Test Method
is equally or, in some instances, more important. The wet
4.1 Methods of Measurement—These test methods are di- traction capability of tires influences both of these measured
vided into two methods: parameters since the tires are the link between theABS and the
4.1.1 Method A—Rectilinear Trajectory Braking, and
pavement and provide the traction or tire adhesion level that
4.1.2 Method B—Curvilinear Trajectory Braking. permits the ABS to function as intended.
4.1.3 Witheachmethod,oneofthreeprocedures(Procedure
5.3 The absolute values of the parameters obtained with
1,2,or3)thatvaryinmeasurementsophisticationmaybeused
these test methods are highly dependent upon the characteris-
to evaluate stopping distance and vehicle uncontrollability.
tics of the vehicle, the design features of theABS, the selected
4.1.4 Procedure 1 is the simplest, with manually recorded
test pavement(s), and the environmental and test conditions
stopping distance and trajectory deviation measurements. Pro-
(for example, ambient temperature, water depths, test speeds)
cedure 2 uses computer data acquisition and non-pavement-
at the test course.Achange in any of these factors may change
contact sensors to measure speed, stopping distance, and yaw
the absolute parameter values and may also change the relative
velocity. Procedure 3 is the most comprehensive; it includes all
rating of tires so tested.
the measurement capabilities of Procedure 2 in addition to the
5.4 These test methods are suitable for research and devel-
recording of steering wheel angle throughout the stopping
opment purposes where tire sets are compared during a brief
maneuver. The measurement procedures for the performance
testing time period. They may not be suitable for regulatory or
parameters are more fully described in Section 11.
specification acceptance purposes because the values obtained
4.2 Method A—Rectilinear Trajectory Braking—This mode
may not necessarily agree or correlate, either in rank order or
of braking traction testing is conducted by bringing the vehicle
absolute value, with those obtained under other conditions (for
to a stop in an intended rectilinear trajectory or straight line
example, different locations or different seasonal time periods
motion, on a split-µ test course. The test may be conducted at
on the same test course).
a series of initial brake application speeds.
6. Test Vehicle
4.3 Method B—Curvilinear Trajectory Braking—This mode
6.1 Test Vehicle—Any commercially available passenger
of braking traction testing is conducted by bringing the vehicle
vehicle equipped with an ABS may be used for the testing.
to a stop on a curvilinear trajectory (curved path) on a uniform
However, it is important that the same vehicle (same model
test surface pavement.The test may be conducted at a series of
initial brake application speeds. year, same version of ABS) be used for all tests in any testing
NOTE 1—Vehicle uncontrollability may be experienced more abruptly program. Different vehicles may give different tire wet traction
F1649 − 20
performance because of their varying handling, suspension, 7.3 Procedure 2—Instrumentation:
and ABS design parameters. 7.3.1 Data Acquisition and Recording System—Provide a
data acquisition system that has the necessary signal condition-
6.1.1 During testing with any selected vehicle, the vehicle
ing (A to D converter, etc.) to provide input to a digital
test mass (driver, fuel, and instrumentation load) shall be
computer to record and store the required test data. The data
maintained to a tolerance of 62%.
acquisition system shall provide recorded data at the rate of at
6.1.2 All tests in any program of tire comparisons shall be
least 100 data points per second per channel.
conducted with the same driver and in the shortest time period
7.3.1.1 The data recording system shall have sufficient
possible for any selected test program.
processing speed and data storage capability for operation at
6.2 Precautions in ABS Vehicle Use—As with any complex
the data acquisition rate as specified in 7.3.1. Data processing
test system, certain precautions shall be exercised in any
(averaging, etc.) after a test run may be conducted by way of
testing program. ABS operation efficiency as a function of
typical computer mathematical algorithms.
brake pad “break-in,” pad operating temperature or fade, or
7.3.1.2 The following data channels (signals) shall be re-
both, pad drag, or any other ABS factor (all of which can
corded during a test run: vehicle speed, km/h (mph); vehicle
change with time and use) should not be allowed to influence
yaw (velocity), m/s (ft/s); and distance traveled after point of
tiretestingoutcome.Ifthereisanydoubtabouttheinfluenceof
test initiation (or brake application), m (ft).
the above or any otherABS operating efficiency factor, a series
7.3.2 Stopping Distance—Speed Measurement—Equip the
of control tire stopping tests on a separate dry surface is
test vehicle with a non-pavement-contact sensor that provides
recommended to quantify the influence of the suspected ABS
the same specifications for vehicle speed (velocity) and stop-
operatingfactors.FollowtheproceduresassetforthinPractice
ping distance as defined in 7.2.1. Record the output from this
F1650forevaluatinganysignificanttimeorothertrendinABS
sensor in the same way using a “brake actuation or other test
operation or efficiency, or both.
initiation system” as described for Procedure 1 in 7.2.1.2.
7.3.3 Trajectory Yaw Deviation—The deviation from in-
7. Test Instrumentation Requirements
tended trajectory is assessed by the special processing of the
7.1 The requirements for test instrumentation are given in yaw (velocity) of the vehicle. This velocity is obtained from a
non-pavement-contact sensor or sensor system that provides a
terms of test instrument specifications rather than citing spe-
cific instruments that perform adequately. As new instrument signal directly proportional to this velocity. For any test, the
signal from this sensor shall be recorded from the point of
design improves capability, the specifications can be revised.
This avoids instrumentation obsolescence in these test meth- brake application or other point of test initiation until the
ods. Appendix X1 provides a list of instrument suppliers that vehicle comes to rest. The accuracy of this velocity measure-
may be capable of meeting the specifications as set forth in ment shall be 62 % or better.
these test methods.
7.4 Procedure 3—Instrumentation:
7.4.1 The instrumentation for stopping distance-speed mea-
7.2 Procedure 1—Instrumentation:
surement shall be as specified in 7.2.1, and the instrumentation
7.2.1 Stopping Distance-Speed Measurement—Equip the
for trajectory deviation shall be as specified in 7.3.3.
test vehicle with a system that provides the following capabili-
7.4.2 Steering Wheel Rotation—Equip the steering wheel of
ties.
thetestvehiclewithatransducerthatrecordstherotationofthe
7.2.1.1 Adigital speed display for the driver, reading to 61
wheel as the driver attempts to maintain vehicle control during
km/h (0.6 mph).
the stopping maneuver. Record left and right rotations as
7.2.1.2 A “test initiation system” that provides a signal
specified in 7.3, as + and – values (signals), and the accuracy
received from the vehicle brake pedal movement or other
of the rotation recording shall be 62° or better.
suitable brake system component, to accurately indicate the
start of the brake actuation process. 7.5 Calibration of Instrumentation—Calibratethespeedand
distance measuring instrumentation by appropriate techniques
7.2.1.3 A distance measuring system that measures the
in accordance with the manufacturer’s instructions. Make
distance along the vehicle or trajectory path from either the
specialsensorcalibrationproceduresbyappropriatetechniques
point of brake application or a well established test initiation
as specified by the manufacturer. The calibration procedure for
velocity obtained from the test initiation system, to the point
“fifth-wheels” shall be as a minimum, in accordance with Test
where the vehicle comes to a stop. This system shall have a
readout in units of distance traversed (meters, feet) and shall Method F457.
have an accuracy of 60.1m(60.3 ft) in a typical stopping
8. Preparation of Test Pavement(s)
distance test.
7.2.2 Orthogonal Trajectory Deviation—Use a distance 8.1 Pavement Selection and Course Layout:
measuring system that can measure the perpendicular distance 8.1.1 Method A—Straight Line Testing—Lay out the test
from the intended trajectory line (TGL) to the center of the pavement (both lanes, see 8.2) with sufficient length to accom-
vehicle in its final rest position after a test. The center of the modate the stopping distance produced by the highest initial
vehicle is defined as the midpoint of the vehicle length and speeds and the poorest performing tires in any planned testing
widthdimension.Thesystemshallhaveanaccuracyof 60.1m program. The length needed at any speed depends on the tires
(60.3 ft). Annex A4 provides a recommended procedure for being tested, the water depths on the surface, and the friction
this measurement for both Methods A and B. levels of both the left and right sections (lanes) of the
F1649 − 20
pavement. Allow sufficient area for vehicle recovery (spinout, coefficient value, with a standard test speed and standard test
plowing). Lay out the two lane test course so that tests may be tire such as specified in Specifications E501, E524,or E1136,
conducted in either direction. or in accordance with Test Method E303, the portable British
8.1.2 Method B—Curvilinear Path Testing—Thepathradius Pendulum Tester, using a standard slider. Conduct sufficient
for a Method B test course must be selected. For any tire set braking trailer test runs (four to six) on each individual surface
and pavement, the cornering force required to negotiate a to obtain a well documented average value. If Test Method
curved path varies as the second power of the speed and E303 is used, assess the friction level as the average of the
inversely with the radius of the curve. Annex A3 provides measured values at ten or more marked and equally spaced
recommendations for selecting the path radius and other locations along the wheel paths of each of the surfaces used for
Method B test details. the testing.
8.1.2.1 Configuration of Curved Test Course—Three op-
8.3.2.2 Method B: Friction Evaluation—Friction evaluation
tions are available for the configuration of the curved course:
for the pavement used for curvilinear path testing by braking
(1) full-circle, (2) half-circle, or (3) quarter-circle. With any of
trailer testing may not be feasible. If trailer testing cannot be
these options an approach lane may be used to enter the test
conducted,usethetechniqueinTestMethodE303asdescribed
course. The selection of one of the three options should be
in 8.3.2.1. At least one common friction evaluation method
made on the basis of the selected path radius and the antici-
should be used for both Methods A and B testing.
pated distance needed to bring the vehicle to a stop for the
8.4 Trajectory Guide Line:
selected maximum speeds. For any configuration, the available
8.4.1 For either MethodAor Method B, aTGLshall be part
stopping distance is a function of the path radius. Annex A3
of the test course layout. This shall be a highly visible (white
provides some information for selecting initial braking actua-
or yellow) 10 to 12 cm (4 to 5 in) wide guide line located on
tion test speeds.
the longitudinal juncture between the low and high friction
8.2 “Split-µ” Surface Layout:
level test lanes or in the center of the curved test course
8.2.1 There are two general approaches for this layout: (1)
pavement.
selection of different paving aggregate-binder combinations
8.5 Application of Water to the Pavement:
(low micro-macro texture vs. high micro-macro texture) in the
8.5.1 Continuously apply water to the pavement with a
initial construction of the test lanes of a wet traction test
system of sprinklers that uniformly applies water to the course.
facility, or (2) the selection of a large area of high traction
AnnexA2 outlines techniques for adjusting and controlling the
pavementandthetreatmentofa3to4m(10to13ft)widelane
water depth on the test course.
of this pavement to reduce the traction level. This treatment
may consist of an epoxy paint or similar durable surface
8.6 Conditioning the Pavement:
coating treatment to produce a modified surface with low
8.6.1 The microtexture of test pavements is subject to
friction level (low microtexture). Either of these approaches
change due to weathering action and actual tire testing (see
may be used.
12.1). Since wet traction should be evaluated on pavements of
8.2.2 With either Method A or B, the course layout should
constant microtexture, such variations can cause problems in
provide for a lateral or cross-slope of 1 to 2 % such that there
evaluation. To reduce or, if possible, avoid this complication,
is a lateral flow of water across the test lanes. The recom-
one or both of the following actions are recommended.
mended direction of flow is from high to low friction level on
8.6.1.1 Condition the pavement by conducting 20 (or more)
the test surfaces if two lanes are used. All individual test
test runs at some selected speed to polish or condition the
surfaces (either lane) shall be of uniform composition, free of
surface, using tires not involved in the test program. The
large cracks and foreign material or debris.
pavement friction evaluation techniques described in 8.3 may
8.3 Magnitude of “Split-µ” Pavement Friction (Traction)
be used for “before” and “after” conditioning testing.
Level:
8.6.1.2 Conduct the testing in accordance with the test plans
8.3.1 Theaveragefrictionlevelforbothofthepavementsas
as specified in Practice F1650. This practice gives data
well as the differential friction level (high vs. low friction test
correction procedures for correcting any trends or transient
lanes) are important test course factors.
changes in pavement or other test conditions by the use of
8.3.2 The difference in friction coefficient between the high
control tires tested on a regular basis with the candidate tires.
and the low test lanes expressed as a ratio [µ (hi)/µ (lo)] shall
be 2.0 or greater. Recommended combinations are 0.50 versus
9. Selection and Preparation of Test Tires
0.20 or 0.45 versus 0.15. The absolute value of the traction or
9.1 For ordinary comparative testing, each four-tire set
friction coefficients will be a function of the measurement
should be of the same age (6 few weeks) and have been stored
techniquesasdescribedin8.3.2.1.IfbothMethodsAandBare
under identical conditions up to the time of initial testing (see
to be used in any test program, use the same friction measure-
also 9.4).
ment technique (same standard tire or slider) for both pave-
ments on both test courses. 9.2 Mount the tires on rims recommended by the appropri-
8.3.2.1 Method A: Lane Friction Evaluation—Friction mea- ate tire standards organizations (for example, Tire and Rim
surements in both lanes may be conducted by using braking Association, ETRTO, JATMA) by using conventional mount-
trailer tests in accordance with Test Method E274 for slide ing procedures with proper bead seating techniques. Use a
coefficient or Test Method E1337 for the more definitive peak suitable type and volume of lubricant.
F1649 − 20
9.3 Tire Break-In—Three options available for tire “break- 11.4 Methods A and B—Procedure 1:
in” are: (1) a simple technique to remove any residue or
11.4.1 Conduct tests at a series of speeds in the range of 48
protuberances, or both, on the tread surface; (2) a technique to
to 88 km/h (30 to 55 mph) or, if possible, a maximum speed
produce a tread surface with a smooth matte finish character-
above 88 km/h (55 mph). Conduct all testing in an “increasing
istic of natural wear; and (3) on-vehicle operation to give the
speed” operation. Approach the test course at the selected
tire a dynamic “running-heat” history to approach an equilib-
initial brake speed. During the approach to the test course,
rium tire shape in addition to some normal wear. The purpose
ensurethatallinstrumentationisoperatingandthatdatawillbe
of (1) and (2) is to avoid any condition that might potentially
acquired throughout the entire test run.
interfere with frictional grip to the pavement. Option (3) is
11.4.2 During the initial part of the run, center the vehicle
selected on the basis that the lack of a dynamic “running-heat”
on the TGL, begin the data acquisition process, and apply the
history might influence performance.
brakes at a location on the test area of the wet pavement that
9.3.1 Option 1—Trim away all protuberances (mold vent
has been previously selected and that is clearly marked.
flash) with a suitable cutting tool. Vigorously wipe the surface
Maintain brake pressure throughout the run.
of the tread with brush and a solvent comprised of 50 %
11.4.3 If the vehicle deviates from the intended trajectory
hydrocarbon liquid (hexane) and 50 % ethanol. This will
during the run, attempt to steer the vehicle in a manner so as to
remove any typical mold release agents.
regain control and maintain the intended trajectory. Continue
9.3.2 Option 2—Verylightlybuffthetireinaccordancewith
with this until vehicle motion ceases.
the procedures set forth in Guide F1046, removing approxi-
11.4.4 At the termination of vehicle motion verify that data
mately 0.2 mm of tread depth across the tread with no
have been recorded as intended and record the stopping
alteration of the profile.
distance to the nearest 0.1 m (0.3 ft).
9.3.3 Option 3—Break in the test tires on a suitable vehicle
11.4.5 Measure the vehicle trajectory deviation, the perpen-
for 80 km (50 miles) at speeds of 95 to 115 km/h (~60 to 70
dicular distance from the TGL to a selected reference point on
mph) under routine interstate highway driving, without pro-
the vehicle. See Annex A4 for details on the vehicle reference
ducing excessive wear during the break-in.
point(s) and recommendations for this procedure.
9.4 Priortothestartoftesting,storethemountedtiresunder
11.4.6 Repeat the operations as specified in 11.4.1 – 11.4.5
conditions that avoid direct sunlight and excessive temperature
for the selected number of replicate runs at each speed. Repeat
increases.
the same procedure for all selected speeds or other operational
9.5 Adjust the tire inflation pressure to the values selected conditions, or both.
for the testing program.
11.4.7 For each candidate set and for each repeated control
set, test data shall be recorded in two tab
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: F1649 − 13 F1649 − 20
Standard Test Methods for
Evaluating Wet Braking Traction Performance of Passenger
Car Tires on Vehicles Equipped with Anti-Lock Braking
Systems
This standard is issued under the fixed designation F1649; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
These test methods cover procedures for measuring the wet braking performance of passenger car
tires when tested on vehicles equipped with an anti-lock braking system (ABS). ABS operation is
accomplished by the use of wheel rotation rate sensors that detect impending wheel lockup and
controllable brake pressure regulators; both of these systems are connected to a control microproces-
sor. When potential lockup is detected for any wheel or pair of wheels, brake pressure is lowered to
forestall the lockup and maintain wheel rotation. This process is repeated until the vehicle comes to
a stop. The necessary lateral force to maintain vehicle control in an emergency braking situation is
only possible when wheel rotation is maintained. Although there may be differences in the braking
performance among the commercially available “vehicle-ABS” combinations, tires may be evaluated
for their relative or comparative wet braking performance with any one “vehicle-ABS-driver”
combination, by the methods as outlined in these test methods.
1. Scope
1.1 These test methods cover the measurement of two types of ABS vehicle behavior that reflect differences in tire wet traction
performance when the vehicle is fitted with a series of different tire sets to be evaluated.
1.1.1 The stopping distance from some selected speed at which the brakes are applied.
1.1.2 The lack of control of the vehicle during the braking maneuver. Uncontrollability occurs when the vehicle does not follow
the intended trajectory during the period of brake application despite a conscious effort on the part of a skilled driver to maintain
trajectory control. Uncontrollability is measured by a series of parameters related to this deviation from the intended trajectory and
the motions that the vehicle makes during the stopping maneuver.
1.1.3 Although anti-lock braking systems maintain wheel rotation and allow for a high degree of trajectory control, different sets
of tires with variations in construction, tread pattern, and tread compound may influence the degree of trajectory control in addition
to stopping distance. Thus vehicle uncontrollability is an important evaluation parameter for tire wet traction performance.
1.2 These test methods specify that the wet braking traction tests be conducted on two specially prepared test courses: (1) a
straight-line (rectilinear) “split-μ” (μ = friction coefficient) test course, with two test lanes deployed along the test course (as
These test methods are under the jurisdiction of ASTM Committee F09 on Tires and is the direct responsibility of Subcommittee F09.20 on Vehicular Testing.
Current edition approved May 1, 2013Oct. 1, 2020. Published June 2013October 2020. Originally approved in 1995. Last previous edition approved in 20032013 as
F1649 – 96 (2003)F1649 – 13. which was withdrawn January 2012 and reinstated in May 2013. DOI: 10.1520/F1649-13.DOI: 10.1520/F1649-20.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F1649 − 20
traveled by the test vehicle); the two lanes have substantially different friction levels such that the left pair of wheels travels on
one surface while the right pair of wheels travels on the other surface; and (2) a curved trajectory constant path radius course with
uniform pavement for both wheel lanes.
1.3 As with all traction testing where vehicle uncontrollability is a likely outcome, sufficient precautions shall be taken to protect
the driver, the vehicle, and the test site facilities from damage due to vehicle traction breakaway during testing. Standard
precautions are roll-bars, secure mounting of all internal instrumentation, driver helmet, and secure seat belt harness, etc.
1.4 The values stated in SI units are to be regarded as the standard. The values given in parenthesis are for information only.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
E274 Test Method for Skid Resistance of Paved Surfaces Using a Full-Scale Tire
E303 Test Method for Measuring Surface Frictional Properties Using the British Pendulum Tester
E501 Specification for Standard Rib Tire for Pavement Skid-Resistance Tests
E524 Specification for Standard Smooth Tire for Pavement Skid-Resistance Tests
E965 Test Method for Measuring Pavement Macrotexture Depth Using a Volumetric Technique
E1136 Specification for P195/75R14 Radial Standard Reference Test Tire
E1337 Test Method for Determining Longitudinal Peak Braking Coefficient (PBC) of Paved Surfaces Using Standard Reference
Test Tire
F457 Test Method for Speed and Distance Calibration of Fifth Wheel Equipped With Either Analog or Digital Instrumentation
F538 Terminology Relating to the Characteristics and Performance of Tires
F1046 Guide for Preparing Artificially Worn Passenger and Light Truck Tires for Testing
F1572 Test Methods for Tire Performance Testing on Snow and Ice Surfaces
F1650 Practice for Evaluating Tire Traction Performance Data Under Varying Test Conditions
F1805 Test Method for Single Wheel Driving Traction in a Straight Line on Snow- and Ice-Covered Surfaces
F1806 Practice for Tire Testing Operations–Basic Concepts and Terminology for Reference Tire Use
F2493 Specification for P225/60R16 97S Radial Standard Reference Test Tire
3. Terminology
3.1 Definitions of Terms Specific to This Standard:
3.1.1 anti-lock braking system (ABS), n—a collection of sensing and control hardware installed on a vehicle to prevent wheel
lockup during brake application. F538
3.1.2 candidate tire, n—a test tire that is part of a test program. F538
3.1.2.1 Discussion—
The term “candidate object” may be used in the same sense as candidate tire.
3.1.3 candidate tire set, n—a set of candidate tires. F538
3.1.4 control tire, n—a reference tire used in a specified manner throughout a test program. F538
3.1.4.1 Discussion—
A control tire may be of either type and typical tire use is the reference (control) tire in Practice F1650 that provides algorithms
for correcting (adjusting) test data for bias trend variations (see Practice F1650 and Annex A1).
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
F1649 − 20
3.1.5 reference tire, n—a special tire included in a test program; the test results for this tire have significance as a base value or
internal benchmark. F538
3.1.6 spinout, n—in tire testing, a type of uncontrollability defined by a loss of steering control due to rapid or substantial yaw,
or both. F538
3.1.7 standard reference test tire, (SRTT), n—a tire that is used as a control tire or surface monitoring tire (for example,
Specification E1136 and F2493 tires). E1136, F1572, F1649, F1650, F1805, F1806, F2493
3.1.7.1 Discussion—
This is a Type 1 reference tire.
3.1.8 stopping distance, n—the path distance (rectilinear or curved) needed to bring a vehicle to a stop from some selected initial
brake application speed. F538
3.1.9 surface monitoring tire, n—a reference tire used to evaluate changes in a test surface over a selected time period. F538
3.1.10 test (or testing), n—a procedure performed on an object (or set of nominally identical objects) using specified equipment
that produces data unique to the object (or set). F538
3.1.10.1 Discussion—
Test data are used to evaluate or model selected properties or characteristics of the object (or set of objects). The scope of testing
depends on the decisions to be made for any program, and sampling and replication plans (see definitions below) need to be
specified for a complete program description.
3.1.10.2 split-μ test—a wet traction or stopping distance test conducted on a test course with substantially different wet friction
levels for the left and right tire test lanes. F538
3.1.10.3 test run—a single pass of a loaded tire over a given test surface. F538
3.1.10.4 traction test—in tire testing, a series of n test runs at a selected operational condition; a traction test is characterized
by an average value for the measured performance parameter. F538
3.1.11 test tire, n—a tire used in a test. F538
3.1.12 test tire set, n—one or more test tires as required by the test equipment or procedure, to perform a test, thereby producing
a single test result. F538
3.1.12.1 Discussion—
The four nominally identical tires required for vehicle stopping distance testing constitute a test tire set. In the discussion below
where the test tire is mentioned, it is assumed that test tire set may be substituted for test tire, if a test tire set is required for the
testing.
3.1.13 trajectory, n—the rectilinear or curvilinear path of a vehicle during a stopping maneuver; it is defined by the center of
gravity and the transient angular orientation of the vehicle. F538
3.1.13.1 intended trajectory—the intended or ideal path (rectilinear or curvilinear) to bring a vehicle to a stop, that is, under
controlled angular orientation. F538
3.1.13.2 orthogonal trajectory deviation—the perpendicular deviation or distance from the center of the vehicle to the TGL at
the end of a stopping test. F538
3.1.13.3 trajectory guide line (TGL)—the centerline marked on the test course pavement that constitutes the intended trajectory;
it is used by the driver to guide or steer the vehicle on its intended path. F538
3.1.14 uncontrollability, n—any deviation of the vehicle from the intended trajectory (TGL) during or at the end of a test, or both.
F538
3.1.14.1 plowing—in tire testing, a type of uncontrollability defined by a loss of steering control with no substantial vehicle yaw;
the vehicle moves on a trajectory that is dictated by vehicle dynamics as determined by velocity, mass, and the available traction
at each tire. F538
F1649 − 20
3.1.15 yaw, n—in a vehicle, the angular motion of a vehicle about its vertical axis through the center of gravity. F538
3.1.15.1 yaw velocity—the magnitude of the yaw (rotation or angular displacement); it may be measured by fore and aft, vehicle
vs. pavement, velocity sensors. F538
4. Summary of Test Method
4.1 Methods of Measurement—These test methods are divided into two methods:
4.1.1 Method A—Rectilinear Trajectory Braking, and
4.1.2 Method B—Curvilinear Trajectory Braking.
4.1.3 With each method, one of three procedures (Procedure 1, 2, or 3) that vary in measurement sophistication may be used to
evaluate stopping distance and vehicle uncontrollability.
4.1.4 Procedure 1 is the simplest, with manually recorded stopping distance and trajectory deviation measurements. Procedure 2
uses computer data acquisition and non-pavement-contact sensors to measure speed, stopping distance, and yaw velocity.
Procedure 3 is the most comprehensive; it includes all the measurement capabilities of Procedure 2 in addition to the recording
of steering wheel angle throughout the stopping maneuver. The measurement procedures for the performance parameters are more
fully described in Section 11.
4.2 Method A—Rectilinear Trajectory Braking—This mode of braking traction testing is conducted by bringing the vehicle to a
stop in an intended rectilinear trajectory or straight line motion, on a split-μ test course. The test may be conducted at a series of
initial brake application speeds.
4.3 Method B—Curvilinear Trajectory Braking—This mode of braking traction testing is conducted by bringing the vehicle to a
stop on a curvilinear trajectory (curved path) on a uniform test surface pavement. The test may be conducted at a series of initial
brake application speeds.
NOTE 1—Vehicle uncontrollability may be experienced more abruptly and with greater frequency with Method B procedures. Therefore, when using
Method B, precautions should be exercised to avoid any possible danger during testing. Testing shall begin with the lowest test velocities selected for
any program and as higher velocities are approached, sufficient care shall be taken to avoid any danger to the driver, the vehicle, and any on-site facilities
during traction breakaway conditions.
NOTE 2—Test speeds lower than 10 km/h are not recommended due to instrumentation insensitivity at this low speed.
4.4 These test methods contain four annexes and one appendix that give important information to assist in the meaningful
evaluation of tire wet traction performance.
4.4.1 Annex A1—Interpretation of Results and Tire Design Feature Evaluation,
4.4.2 Annex A2—Techniques for Water Application and Control,
4.4.3 Annex A3—Selecting Path Radius and Test Speed for Method B Testing,
4.4.4 Annex A4—Measuring Orthogonal Trajectory Deviation (Procedure 1), and
4.4.5 Appendix X1—List of Instrumentation Suppliers.
5. Significance and Use
5.1 Braking traction is an important factor in vehicle control especially on wet pavements. These test methods permit an evaluation
of tires for their relative or comparative performance on an ABS-equipped vehicle. See Annex A1 for background information for
interpretation of results and meaningful evaluation of tire design features for their influence on wet traction performance.
5.2 Although stopping distance is important for vehicle control, the ability to steer the vehicle on a selected trajectory is equally
F1649 − 20
or, in some instances, more important. The wet traction capability of tires influences both of these measured parameters since the
tires are the link between the ABS and the pavement and provide the traction or tire adhesion level that permits the ABS to function
as intended.
5.3 The absolute values of the parameters obtained with these test methods are highly dependent upon the characteristics of the
vehicle, the design features of the ABS, the selected test pavement(s), and the environmental and test conditions (for example,
ambient temperature, water depths, test speeds) at the test course. A change in any of these factors may change the absolute
parameter values and may also change the relative rating of tires so tested.
5.4 These test methods are suitable for research and development purposes where tire sets are compared during a brief testing time
period. They may not be suitable for regulatory or specification acceptance purposes because the values obtained may not
necessarily agree or correlate, either in rank order or absolute value, with those obtained under other conditions (for example,
different locations or different seasonal time periods on the same test course).
6. Test Vehicle
6.1 Test Vehicle—Any commercially available passenger vehicle equipped with an ABS may be used for the testing. However, it
is important that the same vehicle (same model year, same version of ABS) be used for all tests in any testing program. Different
vehicles may give different tire wet traction performance because of their varying handling, suspension, and ABS design
parameters.
6.1.1 During testing with any selected vehicle, the vehicle test mass (driver, fuel, and instrumentation load) shall be maintained
to a tolerance of 62 %.
6.1.2 All tests in any program of tire comparisons shall be conducted with the same driver and in the shortest time period possible
for any selected test program.
6.2 Precautions in ABS Vehicle Use—As with any complex test system, certain precautions shall be exercised in any testing
program. ABS operation efficiency as a function of brake pad “break-in,” pad operating temperature or fade, or both, pad drag,
or any other ABS factor (all of which can change with time and use) should not be allowed to influence tire testing outcome. If
there is any doubt about the influence of the above or any other ABS operating efficiency factor, a series of control tire stopping
tests on a separate dry surface is recommended to quantify the influence of the suspected ABS operating factors. Follow the
procedures as set forth in Practice F1650 for evaluating any significant time or other trend in ABS operation or efficiency, or both.
7. Test Instrumentation Requirements
7.1 The requirements for test instrumentation are given in terms of test instrument specifications rather than citing specific
instruments that perform adequately. As new instrument design improves capability, the specifications can be revised. This avoids
instrumentation obsolescence in these test methods. Appendix X1 provides a list of instrument suppliers that may be capable of
meeting the specifications as set forth in these test methods.
7.2 Procedure 1—Instrumentation:
7.2.1 Stopping Distance-Speed Measurement—Equip the test vehicle with a system that provides the following capabilities.
7.2.1.1 A digital speed display for the driver, reading to 61 km/h (0.6 mph).
7.2.1.2 A “test initiation system” that provides a signal received from the vehicle brake pedal movement or other suitable brake
system component, to accurately indicate the start of the brake actuation process.
7.2.1.3 A distance measuring system that measures the distance along the vehicle or trajectory path from either the point of brake
application or a well established test initiation velocity obtained from the test initiation system, to the point where the vehicle
comes to a stop. This system shall have a readout in units of distance traversed (metres,(meters, feet) and shall have an accuracy
of 60.1 m (60.3 ft) in a typical stopping distance test.
7.2.2 Orthogonal Trajectory Deviation—Use a distance measuring system that can measure the perpendicular distance from the
intended trajectory line (TGL) to the center of the vehicle in its final rest position after a test. The center of the vehicle is defined
F1649 − 20
as the midpoint of the vehicle length and width dimension. The system shall have an accuracy of 60.1 m (60.3 ft). Annex A4
provides a recommended procedure for this measurement for both Methods A and B.
7.3 Procedure 2—Instrumentation:
7.3.1 Data Acquisition and Recording System—Provide a data acquisition system that has the necessary signal conditioning (A to
D converter, etc.) to provide input to a digital computer to record and store the required test data. The data acquisition system shall
provide recorded data at the rate of at least 100 data points per second per channel.
7.3.1.1 The data recording system shall have sufficient processing speed and data storage capability for operation at the data
acquisition rate as specified in 7.3.1. Data processing (averaging, etc.) after a test run may be conducted by way of typical computer
mathematical algorithms.
7.3.1.2 The following data channels (signals) shall be recorded during a test run: vehicle speed, km/h (mph); vehicle yaw
(velocity), m/s (ft/s); and distance traveled after point of test initiation (or brake application), m (ft).
7.3.2 Stopping Distance—Speed Measurement—Equip the test vehicle with a non-pavement-contact sensor that provides the same
specifications for vehicle speed (velocity) and stopping distance as defined in 7.2.1. Record the output from this sensor in the same
way using a “brake actuation or other test initiation system” as described for Procedure 1 in 7.2.1.2.
7.3.3 Trajectory Yaw Deviation—The deviation from intended trajectory is assessed by the special processing of the yaw (velocity)
of the vehicle. This velocity is obtained from a non-pavement-contact sensor or sensor system that provides a signal directly
proportional to this velocity. For any test, the signal from this sensor shall be recorded from the point of brake application or other
point of test initiation until the vehicle comes to rest. The accuracy of this velocity measurement shall be 62 % or better.
7.4 Procedure 3—Instrumentation:
7.4.1 The instrumentation for stopping distance-speed measurement shall be as specified in 7.2.1, and the instrumentation for
trajectory deviation shall be as specified in 7.3.3.
7.4.2 Steering Wheel Rotation—Equip the steering wheel of the test vehicle with a transducer that records the rotation of the wheel
as the driver attempts to maintain vehicle control during the stopping maneuver. Record left and right rotations as specified in 7.3,
as + and – values (signals), and the accuracy of the rotation recording shall be 62° or better.
7.5 Calibration of Instrumentation—Calibrate the speed and distance measuring instrumentation by appropriate techniques in
accordance with the manufacturer’s instructions. Make special sensor calibration procedures by appropriate techniques as specified
by the manufacturer. The calibration procedure for “fifth-wheels” shall be as a minimum, in accordance with Test Method F457.
8. Preparation of Test Pavement(s)
8.1 Pavement Selection and Course Layout:
8.1.1 Method A—Straight Line Testing—Lay out the test pavement (both lanes, see 8.2) with sufficient length to accommodate the
stopping distance produced by the highest initial speeds and the poorest performing tires in any planned testing program. The
length needed at any speed depends on the tires being tested, the water depths on the surface, and the friction levels of both the
left and right sections (lanes) of the pavement. Allow sufficient area for vehicle recovery (spinout, plowing). Lay out the two lane
test course so that tests may be conducted in either direction.
8.1.2 Method B—Curvilinear Path Testing—The path radius for a Method B test course must be selected. For any tire set and
pavement, the cornering force required to negotiate a curved path varies as the second power of the speed and inversely with the
radius of the curve. Annex A3 provides recommendations for selecting the path radius and other Method B test details.
8.1.2.1 Configuration of Curved Test Course—Three options are available for the configuration of the curved course: (1)
full-circle, (2) half-circle, or (3) quarter-circle. With any of these options an approach lane may be used to enter the test course.
The selection of one of the three options should be made on the basis of the selected path radius and the anticipated distance needed
to bring the vehicle to a stop for the selected maximum speeds. For any configuration, the available stopping distance is a function
of the path radius. Annex A3 provides some information for selecting initial braking actuation test speeds.
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8.2 “Split-μ” Surface Layout:
8.2.1 There are two general approaches for this layout: (1) selection of different paving aggregate-binder combinations (low
micro-macro texture vs. high micro-macro texture) in the initial construction of the test lanes of a wet traction test facility, or (2)
the selection of a large area of high traction pavement and the treatment of a 3 to 4 m (9(10 to 1213 ft) wide lane of this pavement
to reduce the traction level. This treatment may consist of an epoxy paint or similar durable surface coating treatment to produce
a modified surface with low friction level (low microtexture). Either of these approaches may be used.
8.2.2 With either Method A or B, the course layout should provide for a lateral or cross-slope of 1 to 2 % such that there is a lateral
flow of water across the test lanes. The recommended direction of flow is from high to low friction level on the test surfaces if
two lanes are used. All individual test surfaces (either lane) shall be of uniform composition, free of large cracks and foreign
material or debris.
8.3 Magnitude of “Split-μ” Pavement Friction (Traction) Level:
8.3.1 The average friction level for both of the pavements as well as the differential friction level (high vs. low friction test lanes)
are important test course factors.
8.3.2 The difference in friction coefficient between the high and the low test lanes expressed as a ratio [μ (hi)/μ (lo)] shall be 2.0
or greater. Recommended combinations are 0.50 versus 0.20 or 0.45 versus 0.15. The absolute value of the traction or friction
coefficients will be a function of the measurement techniques as described in 8.3.2.1. If both Methods A and B are to be used in
any test program, use the same friction measurement technique (same standard tire or slider) for both pavements on both test
courses.
8.3.2.1 Method A: Lane Friction Evaluation—Friction measurements in both lanes may be conducted by using braking trailer tests
in accordance with Test Method E274 for slide coefficient or Test Method E1337 for the more definitive peak coefficient value,
with a standard test speed and standard test tire such as specified in Specifications E501, E524, or E1136, or in accordance with
Test Method E303, the portable British Pendulum Tester, using a standard slider. Conduct sufficient braking trailer test runs (four
to six) on each individual surface to obtain a well documented average value. If Test Method E303 is used, assess the friction level
as the average of the measured values at ten or more marked and equally spaced locations along the wheel paths of each of the
surfaces used for the testing.
8.3.2.2 Method B: Friction Evaluation—Friction evaluation for the pavement used for curvilinear path testing by braking trailer
testing may not be feasible. If trailer testing cannot be conducted, use the technique in Test Method E303 as described in 8.3.2.1.
At least one common friction evaluation method should be used for both Methods A and B testing.
8.4 Trajectory Guide Line:
8.4.1 For either Method A or Method B, a TGL shall be part of the test course layout. This shall be a highly visible (white or
yellow) 10 to 12 cm (4 to 5 in) wide guide line located on the longitudinal juncture between the low and high friction level test
lanes or in the center of the curved test course pavement.
8.5 Application of Water to the Pavement:
8.5.1 Continuously apply water to the pavement with a system of sprinklers that uniformly applies water to the course. Annex A2
outlines techniques for adjusting and controlling the water depth on the test course.
8.6 Conditioning the Pavement:
8.6.1 The microtexture of test pavements is subject to change due to weathering action and actual tire testing (see 12.1). Since
wet traction should be evaluated on pavements of constant microtexture, such variations can cause problems in evaluation. To
reduce or, if possible, avoid this complication, one or both of the following actions are recommended.
8.6.1.1 Condition the pavement by conducting 20 (or more) test runs at some selected speed to polish or condition the surface,
using tires not involved in the test program. The pavement friction evaluation techniques described in 8.3 may be used for “before”
and “after” conditioning testing.
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8.6.1.2 Conduct the testing in accordance with the test plans as specified in Practice F1650. This practice gives data correction
procedures for correcting any trends or transient changes in pavement or other test conditions by the use of control tires tested on
a regular basis with the candidate tires.
9. Selection and Preparation of Test Tires
9.1 For ordinary comparative testing, each four-tire set should be of the same age (6 few weeks) and have been stored under
identical conditions up to the time of initial testing (see also 9.4).
9.2 Mount the tires on rims recommended by the appropriate tire standards organizations (for example, Tire and Rim Association,
ETRTO, JATMA) by using conventional mounting procedures with proper bead seating techniques. Use a suitable type and volume
of lubricant.
9.3 Tire Break-In—Three options available for tire “break-in” are: (1) a simple technique to remove any residue or protuberances,
or both, on the tread surface; (2) a technique to produce a tread surface with a smooth matte finish characteristic of natural wear;
and (3) on-vehicle operation to give the tire a dynamic “running-heat” history to approach an equilibrium tire shape in addition
to some normal wear. The purpose of (1) and (2) is to avoid any condition that might potentially interfere with frictional grip to
the pavement. Option (3) is selected on the basis that the lack of a dynamic “running-heat” history might influence performance.
9.3.1 Option 1—Trim away all protuberances (mold vent flash) with a suitable cutting tool. Vigorously wipe the surface of the
tread with brush and a solvent comprised of 50 % hydrocarbon liquid (hexane) and 50 % ethanol. This will remove any typical
mold release agents.
9.3.2 Option 2—Very lightly buff the tire in accordance with the procedures set forth in Guide F1046, removing approximately
0.2 mm of tread depth across the tread with no alteration of the profile.
9.3.3 Option 3—Break in the test tires on a suitable vehicle for 80 km (50 miles) at speeds of 95 to 115 km/h (60(~60 to 70 mph)
under routine interstate highway driving, without producing excessive wear during the break-in.
9.4 Prior to the start of testing, store the mounted tires under conditions that avoid direct sunlight and excessive temperature
increases.
9.5 Adjust the tire inflation pressure to the values selected for the testing program.
10. Vehicle Preparation
10.1 Install the instrumentation as specified by the procedure selected for the testing. Ensure that all instrumentation is operating
in accordance with specifications.
10.2 Ensure that the ABS is in normal operating condition.
10.3 Adjust the vehicle load (mass) as specified in 6.1.
11. Test Procedure
11.1 Preliminary Actions—Set up the watering system to apply water to the test surface for a period of at least 30 min prior to
testing to make any adjustments needed and to allow the surface to become thoroughly saturated and stabilized.
11.2 Assemble all the sets of tires to be tested in any evaluation program or for daily testing. Select the test speeds to be used and
the order in which the sets of tires will be tested. For any selected order, a test sequence is established with a control tire set tested
at regular intervals among the selected candidate sets. Select the number of test runs or replicates for both control and candidate
tires. A complete test for a tire set is comprised of n replicate test runs for each selected speed.
11.3 Select from Practice F1650 a test plan that specifies the frequency of control tire tests. This practice also gives the procedure
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for correcting for any variation or drift in testing conditions as well as the necessary calculations for evaluating the Traction
Performance Index (TPI), that gives a comparative rating of all candidate tire sets tested (see 12.1).
11.4 Methods A and B—Procedure 1:
11.4.1 Conduct tests at a series of speeds in the range of 48 to 88 km/h (30 to 55 mph) or, if possible, a maximum speed above
88 km/h (55 mph). Conduct all testing in an “increasing speed” operation. Approach the test course at the selected initial
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