1、Designation: F 408 99Standard 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 revision, the year
2、 of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 or light trucks.S
3、uch 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 not purport to ad
4、dress 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 Standards:E 274 Test Me
5、thod for Skid Resistance of Paved SurfacesUsing a Full-Scale Tire2E 1337 Test Method for Determining Longitudinal PeakBraking Coefficient of Paved Surfaces Using a StandardReference Test Tire2F 377 Practice for Calibration of Braking/Tractive Measur-ing Devices for Testing Tires3F 457 Test Method fo
6、r Speed and Distance Calibration of aFifth Wheel Equipped With Either Analog or DigitalInstrumentation3F 538 Terminology Relating to the Characteristics and Per-formance of Tires3F 1650 Practice for Evaluating Tire Traction PerformanceData Under Varying Test Conditions33. Terminology3.1 Definitions:
7、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 braking force co
8、efficient 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. F 5383.1.
9、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 5383.1.8 nor
10、mal 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 the tire-axi
11、s 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 chosen to
12、make the axissystem orthogonal and right-hand.3.1.11.1 DiscussionSee Fig. 1. F 5383.1.12 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 about the wheel spin axis.3.1.13.1 DiscussionDriving tor
13、que 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 conducted on tires mounted on atrailer towed by a veh
14、icle. Brakes are applied firmly until oneor both test tire(s) are locked and then held locked for a period1This test method is under the jurisdiction of ASTM Committee F-9 on Tires andis the direct responsibility of Subcommittee F09.20 on Dynamic Response.Current edition approved Sept. 10, 1999. Pub
15、lished October 1999. Originallypublished as F 408 75. Last previous edition F 408 94a.2Annual Book of ASTM Standards, Vol 04.03.3Annual Book of ASTM Standards, Vol 09.02.1Copyright ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.of at least 1.5 s at speeds ranging from 3
16、2 km/h (20 mph) to 96km/h (60 mph).4.2 Recommended vehicle test speeds are: 32, 64, and 96km/h (20, 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 conditio
17、ns (ambient androad surface temperature, humidity, wind speed and direction,purity and film depth of 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 the
18、se factors maychange the measurements on a subsequent run of the test.5.2 These test methods are suitable 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 o
19、btained maynot necessarily agree or correlate either in rank order orabsolute traction performance 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
20、 with other testprocedures.6. Apparatus6.1 The apparatus consists of tow vehicle and trailer. Ve-hicle 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 spe
21、eds in the range from 32 to 96 km/h (20to 60 mph), which are to be kept constant to within 0.8 km/h(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 wat
22、er tank to store sufficient water to supply thewatering system unless external watering is used,6.2.2.3 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 cont
23、rol brakelinepressure, brake application rate, and water application rate.6.3 Towed Trailer The trailer 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 r
24、ange ofpassenger car and light truck rim sizes to be tested.6.3.1 The hitch height shall be no higher 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 s
25、oarranged that the trailer tires will run in tracks separate fromthe tire tracks of the tow vehicle. 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
26、 % of the appropriate maximumload as specified in the current yearbook of the appropriate tireand rim 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 t
27、he test wheels shall be equipped with atypical or special automotive hydraulic brake system which canapply 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
28、 and camber to within 60.05with maximum vertical suspension displacements. Suspensionarms and bushings 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
29、 such a design as toisolate suspension resonance.6.3.5 The brake application system shall be able to 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.6.3.6 The trailer may be optionally equipped with apavement-wet
30、ting system, less the storage tank, which ismounted on the tow 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 spl
31、ash and over-spray (see Note 1). The nozzleconfiguration and 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. Th
32、e nozzle shall be located 25 mm (1 in.) abovethe pavement or the minimum height required to clear ob-stacles which the tester is expected to encounter, but in no caseFIG. 1 Tire-Axis SystemF 4082more than 100 mm (4 in.) above the pavement. The water layershall be at least 25 mm (1 in.) wider than th
33、e test tire tread andapplied so the tire is centrally located between the edges. Thevolume 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
34、surface. The rate of waterapplication at speeds of 64 and 96 km/h (40 and 60 mph) shallbe 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 reas
35、onably clean and contain nochemicals such as wetting agents or detergents.NOTE 1A suitable nozzle design is described in detail in Test MethodE 274.6.4 Instrumentation Each test wheel position on thetrailer shall be equipped with a wheel rotational velocitymeasuring system and with transducers to me
36、asure the brakingforce and vertical load at the test wheel.6.4.1 General Requirements for Measurement 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 verticallo
37、ad or traction force from 450 N (100 lbf) to full scale,6.4.1.2 Overall system accuracy, speed: 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 tes
38、t sequences. The calibration signalshall be at least 50 % of the full scale for the transducer, 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
39、 regular operation.6.4.2 Vehicle Speed To measure vehicle speed, a fifthwheel or non-contact 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
40、 have speci-fications in accordance with Test Method F 457.6.4.3 Braking Forces The braking force-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. Thetrans
41、ducer design and location shall minimize inertial effectsand vibration induced mechanical resonance. 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 f
42、ull scale.The transducer shall be installed in such a manner as toexperience less than 1 angular rotation with respect to itsmeasuring axes at a maximum expected braking torque.6.4.4 Vertical Load The vertical load-measuring trans-ducer shall measure the vertical load at each test wheel duringbrake
43、application. The transducer shall have the same specifi-cations as those described in 6.4.3.6.4.5 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. Addi
44、tionally, it shall have thefollowing specifications:6.4.5.1 Minimum Frequency Responsed-c flat (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 s
45、hall be sufficient to permit full-scale displayfor full-scale input signal level,6.4.5.5 Input 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 readin
46、g shall notexceed 1 % full scale when subjected to vibrational accelera-tion of 49.0 m/s2(5 gs) 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
47、 Chart recorders, if used, shall have an adjustablechart speed capable of at least 25 mm/s.6.4.6 Power Supply The 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 ti
48、res should be approximately of the same age andhave been stored essentially at the same conditions.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 st
49、andards 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-in mileage should be accumulated for a giventire equally on the front and rear axles of the vehicle used forbreak-in operation. Break-in the test tires for a minimum of 80km (50 miles) at test load and infla
