1、Designation:F40899(Reapproved 2015)Standard Test Method forTires for Wet Traction in Straight-Ahead Braking,Using aTowed Trailer1This standard is issued under the fixed designation F408;the number immediately following the designation indicates the year of originaladoption or,in the case of revision
2、,the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscriptepsilon()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.
3、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 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:2E274 Test Method
5、 for Skid Resistance of Paved SurfacesUsing a Full-Scale TireE1337 Test Method for Determining Longitudinal PeakBraking Coefficient of Paved Surfaces Using StandardReference Test TireF377 Practice for Calibration of Braking/Tractive MeasuringDevices for Testing TiresF457 Test Method for Speed and Di
6、stance Calibration ofFifth Wheel Equipped With Either Analog or DigitalInstrumentationF538 Terminology Relating to the Characteristics and Per-formance of TiresF1650 Practice for Evaluating Tire Traction PerformanceData Under Varying Test Conditions3.Terminology3.1 Definitions:3.1.1 braking force,F,
7、nof a tire,the negative longitu-dinal force resulting from braking torque application.F5383.1.2 braking force coeffcient,nof a tire,the ratio ofbraking force to normal force.F5383.1.3 braking force coeffcient,peak,nof a tire,the maxi-mum value of tire braking force coefficient that occurs prior towh
8、eel lockup as the braking torque is progressively increased.F5383.1.4 braking force coeffcient,slide,nof a tire,the valueof braking force coefficient obtained on a locked wheel.F5383.1.5 braking torque,ML2/T2,nof a vehicle,thenegative wheel torque.F5383.1.6 lockup,nof a wheel,the condition of a whee
9、l 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 X direction.F5383.1.8 normal force,F,nof a tire,the component of a tireforce
10、vector in the Z direction.F5383.1.9 skid number(SN),nslide braking force coefficientmultiplied by 100.F5383.1.10 test run,na single pass of a loaded tire over a giventest surface.F5383.1.11 tire axis system,nthe origin of the tire-axis systemis the center of the tire contact where the X-axis is thei
11、ntersection of the wheel plane and the road plane with apositive direction forward,the Z-axis is perpendicular to theroad plane with a positive direction downward,and the Y-axisis in the road plane,its direction being chosen to make the axissystem orthogonal and right-hand.3.1.11.1 DiscussionSee Fig
12、.1.F5383.1.12 tire forces,F,nthe external forces acting on a tireby the road.F5383.1.13 torque,FL,nof a wheel,the external torqueapplied to a tire from a vehicle about the wheel spin axis.3.1.13.1 DiscussionDriving torque is positive wheeltorque;braking torque is negative wheel torque.F5381This test
13、 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 1,2015.Published June 2015.Originallyapproved in 1975.Last previous edition approved in 2008 as F408 99(2008).DOI:10.1520/F0408-99
14、R15.2For 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 onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700
15、,West Conshohocken,PA 19428-2959.United States1 3.1.14 vertical load,nthe normal reaction of the tire onthe road which is equal to the negative of the normal force.F5384.Summary of Test Method4.1 The measurements are conducted on tires mounted on atrailer towed by a vehicle.Brakes are applied firmly
16、 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(20,40,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
