1、Designation: F 408 99 (Reapproved 2008)Standard Test Method forTires for Wet Traction in Straight-Ahead Braking, Using aTowed Trailer1This standard is issued under the fixed designation F 408; the number immediately following the designation indicates the year oforiginal adoption or, in the case of
2、revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the measurement of brakingtraction of tires designed for passenger cars
3、or light trucks.Such braking traction measurements are applicable to condi-tions wherein the vehicle is traveling straight ahead on a wet,paved surface.1.2 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.3 This standard does
4、not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standa
5、rds:2E 274 Test Method for Skid Resistance of Paved SurfacesUsing a Full-Scale TireE 1337 Test Method for Determining Longitudinal PeakBraking Coefficient of Paved Surfaces Using a StandardReference Test TireF 377 Practice for Calibration of Braking/Tractive Measur-ing Devices for Testing TiresF 457
6、 Test Method for Speed and Distance Calibration ofFifth Wheel Equipped With Either Analog or DigitalInstrumentationF 538 Terminology Relating to the Characteristics and Per-formance of TiresF 1650 Practice for Evaluating Tire Traction PerformanceData Under Varying Test Conditions3. Terminology3.1 De
7、finitions:3.1.1 braking force, F, nof a tire, the negative longitu-dinal force resulting from braking torque application. F 5383.1.2 braking force coeffcient, nof a tire, the ratio ofbraking force to normal force. F 5383.1.3 braking force coeffcient, peak, nof a tire, themaximum value of tire brakin
8、g force coefficient that occursprior to wheel lockup as the braking torque is progressivelyincreased. F 5383.1.4 braking force coeffcient, slide, nof a tire, the valueof braking force coefficient obtained on a locked wheel.F 5383.1.5 braking torque, ML2/T2, nof a vehicle, the nega-tive wheel torque.
9、 F 5383.1.6 lockup, nof a wheel, the condition of a wheel inwhich its rotational velocity about the wheel spin axis is zeroand it is prevented from rotating in the presence of appliedwheel torque.3.1.7 longitudinal force, F, nof a tire, the component ofthe tire force vector in the X8 direction. F 53
10、83.1.8 normal force, F, nof a tire, the component of a tireforce vector in the Z8 direction. F 5383.1.9 skid number (SN), nslide braking force coefficientmultiplied by 100. F 5383.1.10 test run, na single pass of a loaded tire over a giventest surface. F 5383.1.11 tire axis system, nthe origin of th
11、e tire-axis systemis the center of the tire contact where the X8-axis is theintersection of the wheel plane and the road plane with apositive direction forward, the Z8-axis is perpendicular to theroad plane with a positive direction downward, and the Y8-axisis in the road plane, its direction being
12、chosen to make the axissystem orthogonal and right-hand.3.1.11.1 DiscussionSee Fig. 1. F 5381This test method is under the jurisdiction of ASTM Committee F09 on Tiresand is the direct responsibility of Subcommittee F09.20 on Vehicular Testing.Current edition approved May 1, 2008. Published June 2008
13、. Originallyapproved in 1975. Last previous edition approved in 1999 as F 408 99.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page
14、 onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.1.12 tire forces, F, nthe external forces acting on a tireby the road. F 5383.1.13 torque, FL, nof a wheel, the external torqueapplied to a tire from a vehicle abo
15、ut the wheel spin axis.3.1.13.1 DiscussionDriving torque is positive wheeltorque; braking torque is negative wheel torque. F 5383.1.14 vertical load, nthe normal reaction of the tire onthe road which is equal to the negative of the normal force.F 5384. Summary of Test Method4.1 The measurements are
16、conducted on tires mounted on atrailer towed by a vehicle. Brakes are applied firmly until oneor both test tire(s) are locked and then held locked for a periodof at least 1.5 s at speeds ranging from 32 km/h (20 mph) to 96km/h (60 mph).4.2 Recommended vehicle test speeds are: 32, 64, and 96km/h (20,
17、 40, and 60 mph).5. Significance and Use5.1 The measured values are traction properties of tiresobtained with the towed trailer described here on a given roadsurface, under given environmental conditions (ambient androad surface temperature, humidity, wind speed and direction,purity and film depth o
18、f water used to wet the road surface).They are carried out in accordance with the stated testprocedures and reflect the performance of the total tire-vehicleenvironmental system. A change in any of these factors maychange the measurements on a subsequent run of the test.5.2 These test methods are su
19、itable for research and devel-opment purposes, where tires are compared during a singleseries of tests. They may not be suitable for regulatory statutesor specification acceptance, because the values obtained maynot necessarily agree or correlate either in rank order orabsolute traction performance
20、level with those obtained onother road surfaces (or the same surface after additional wear),under other environmental conditions, or other towed trailers,or other test devices, or with results obtained with other testprocedures.6. Apparatus6.1 The apparatus consists of tow vehicle and trailer. Ve-hi
21、cle and trailer must comply with all applicable state andfederal laws when operated on public roads.6.2 Tow Vehicle:6.2.1 The tow vehicle shall have the capability of towing thetrailer at specified speeds in the range from 32 to 96 km/h (20to 60 mph), which are to be kept constant to within 0.8 km/h
22、(0.5 mph), even at maximum level of application of brakingforces.6.2.2 The tow vehicle shall be equipped with the followingaccessories:6.2.2.1 Equipment to actuate brakes on towed trailer,6.2.2.2 A water tank to store sufficient water to supply thewatering system unless external watering is used,6.2
23、.2.3 Recording equipment to record signals from trans-ducers installed on the towed trailer,6.2.2.4 Hitch with adjustable height for towing the trailer,and6.2.2.5 Optional equipment to monitor and control brakelinepressure, brake application rate, and water application rate.6.3 Towed TrailerThe trai
24、ler shall be equipped with a towhitch and one or two test wheels which shall be instrumentedas described. A self-watering system is optional (see 6.3.6).Trailers shall be designed to accommodate the range ofpassenger car and light truck rim sizes to be tested.6.3.1 The hitch height shall be no highe
25、r than the loaded tireradius, and the distance from hitch ball to axle centerline shallbe no less than ten times the hitch height. For externalwatering, the trailer hitch on the tow vehicle shall be soarranged that the trailer tires will run in tracks separate fromthe tire tracks of the tow vehicle.
26、 The minimum track offset ofthe test tire(s) with respect to the track of the tow vehiclesshould be 0.3 m (12 in.).6.3.2 The trailer shall have provisions for adjustment ofvertical load from 65 to 110 % of the appropriate maximumload as specified in the current yearbook of the appropriate tireand ri
27、m standards organization. To meet this requirement forall rim sizes, two or more trailers designed for different loadranges and equipped with appropriate wheel adaptors may benecessary.6.3.3 Each of the test wheels shall be equipped with atypical or special automotive hydraulic brake system which ca
28、napply sufficient braking torque to initiate and maintain lockupof the test wheel(s) for the duration of the test.6.3.4 Each of the test wheels shall have a suspensioncapable of limiting change of toe and camber to within 60.05with maximum vertical suspension displacements. Suspensionarms and bushin
29、gs shall have sufficient rigidity necessary tominimize free play and compliance under application ofmaximum braking forces. The suspension system shall provideadequate load-carrying capacity and be of such a design as toisolate suspension resonance.6.3.5 The brake application system shall be able to
30、 controlthe time interval between initial brake application and wheellockup within a range of 0.2 to 0.5 s with a repeatability of60.1 s.FIG. 1 Tire-Axis SystemF 408 99 (2008)26.3.6 The trailer may be optionally equipped with apavement-wetting system, less the storage tank, which ismounted on the to
31、w vehicle. The water being applied to thepavement ahead of the test tires shall be supplied by a nozzlesuitably designed to ensure the water layer encountered by thetest tire has a uniform cross section at all test speeds with aminimum splash and over-spray (see Note 1). The nozzleconfiguration and
32、position shall ensure that the water jets shallbe directed toward the test tire and pointed toward thepavement at an angle of 20 to 30. The water shall strike thepavement 0.25 to 0.46 m (10 to 18 in.) ahead of the center oftire contact. The nozzle shall be located 25 mm (1 in.) abovethe pavement or
33、the minimum height required to clear ob-stacles which the tester is expected to encounter, but in no casemore than 100 mm (4 in.) above the pavement. The water layershall be at least 25 mm (1 in.) wider than the test tire tread andapplied so the tire is centrally located between the edges. Thevolume
34、 of water per unit of wetted width shall be directlyproportional to the test speed. The quantity of water applied at32 km/h (20 mph) shall be 300 mL/min per mm of width (2.0gal/min per inch of width) of wetted surface. The rate of waterapplication at speeds of 64 and 96 km/h (40 and 60 mph) shallbe
35、600 and 900 mL/min per mm of width (4.0 and 6.0 gal/minper inch of width) of wetted surface, respectively. The nominalvalues of rate of water application shall be maintained within610 %. The water shall be reasonably clean and contain nochemicals such as wetting agents or detergents.NOTE 1A suitable
36、 nozzle design is described in detail in Test MethodE 274.6.4 InstrumentationEach test wheel position on the trailershall be equipped with a wheel rotational velocity measuringsystem and with transducers to measure the braking force andvertical load at the test wheel.6.4.1 General Requirements for M
37、easurement SystemTheinstrumentation system shall conform to the following overallrequirements at ambient temperatures between 0 and 43C (32and 110F):6.4.1.1 Overall system accuracy, force: 61.5 % of verticalload or traction force from 450 N (100 lbf) to full scale,6.4.1.2 Overall system accuracy, sp
38、eed: 61.5 % of speed or60.8 km/h (60.5 mph), whichever is greater,6.4.1.3 Shunt CalibrationAll strain-gage transducers shallbe equipped with shunt calibration resistors that can beconnected before or after test sequences. The calibration signalshall be at least 50 % of the full scale for the transdu
39、cer, and6.4.1.4 RuggednessThe exposed portions of the systemshall tolerate 100 % relative humidity (rain or spray) and allother adverse conditions such as dust, shock, and vibrationswhich may be encountered in regular operation.6.4.2 Vehicle SpeedTo measure vehicle speed, a fifthwheel or non-contact
40、 precision speed-measuring system shouldbe used. Output shall be directly visable to the driver and shallbe simultaneously recorded. The fifth wheel or precisionspeedometer used to measure vehicle speed shall have speci-fications in accordance with Test Method F 457.6.4.3 Braking ForcesThe braking f
41、orce-measuring trans-ducers shall measure longitudinal force generated at thetire-road interface as a result of brake application within arange from 0 to at least 125 % of the applied vertical load. Thetransducer design and location shall minimize inertial effectsand vibration induced mechanical res
42、onance. The transducershall have an output directly proportional to the force with lessthan 1 % hysteresis and less than 1 % nonlinearity at full scale.It shall have less than 2 % cross-axis sensitivity at full scale.The transducer shall be installed in such a manner as toexperience less than 1 angu
43、lar rotation with respect to itsmeasuring axes at a maximum expected braking torque.6.4.4 Vertical LoadThe vertical load-measuring trans-ducer shall measure the vertical load at each test wheel duringbrake application. The transducer shall have the same specifi-cations as those described in 6.4.3.6.
44、4.5 Signal Conditioning and Recording SystemAll sig-nal conditioning and recording equipment shall provide linearoutput with necessary gain and data reading resolution to meetthe requirements of 6.4.1. Additionally, it shall have thefollowing specifications:6.4.5.1 Minimum Frequency Responsed-c flat
45、 (61%)to30 Hz full scale,6.4.5.2 Tire vertical load, braking force, vehicle and wheelspeeds and a time base must be recorded in phase (0 to 30 Hz65),6.4.5.3 Signal-to-Noise Ratioat least 20/1,6.4.5.4 Gain shall be sufficient to permit full-scale displayfor full-scale input signal level,6.4.5.5 Input
46、 impedance shall be at least ten times largerthan the output impedance of the signal source,6.4.5.6 It must be insensitive to vibrations, acceleration, andchanges in ambient temperature. The error in reading shall notexceed 1 % full scale when subjected to vibrational accelera-tion of 49.0 m/s2(5 gs
47、) in the 0.5 to 40-Hz frequency rangeand operating temperature range from 0C (32F) to 43C(110F),6.4.5.7 It shall not be affected by storage temperaturevariations between 29C (20F) and 71C (160F), and6.4.5.8 Chart recorders, if used, shall have an adjustablechart speed capable of at least 25 mm/s.6.4
48、.6 Power SupplyThe power supply for transducers andrecording system shall meet or exceed requirements specifiedby transducer and recorder manufacturers.7. Selection and Preparation of Test Tires7.1 Test tires should be approximately of the same age andhave been stored essentially at the same conditi
49、ons.7.2 Trim the test tires to remove all protuberances on thetread surface caused by mold air vents or flashes at moldjunctions.7.3 Mount the test tires on rims specified by the appropriatetire and rim standards organization using conventional mount-ing methods. Ensure proper bead seating by the use of asuitable lubricant and the subsequent warm-up procedures.Excessive use of lubricant should be avoided to preventslipping of the tire on the wheel rim.7.4 Tire break-in may be used to improve repeatability ofresults. Break
