ASTM_F_424_-_98.pdf

Designation:F 424 98Standard Test Method forTires for Wet Driving Traction in Straight-Ahead MotionUsing Highway Vehicles1This standard is issued under the fixed designation F 424;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year 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 drivingtraction of tires designed for and to be mounted on cars ortrucks traveling straight ahead on a prepared surface.1.2 This standard does 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.1.3 The values stated in SI units are to be regarded as thestandard.The values given in parentheses are for informationonly.2.Referenced Documents2.1 ASTM Standards:E 274 Test Method 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 for Speed and Distance Calibration of aFifth Wheel Equipped with Either Analog or DigitalInstrumentation3F 538 Terminology Relating to the Characteristics and Per-formance of Tires33.Terminology3.1 Definitions:3.1.1 driving coeffcient(nd),nthe ratio of the drivingforce to the normal force.(F 538)3.1.2 driving coeffcient,peak(nd),nthe maximum valueof the driving coefficient.(F 538)3.1.3 driving force,F,nof a tire,the positive longitu-dinal force resulting from the application of driving torque.(F 538)3.1.4 driving torque,ML2/T2,nof a wheel,the positivewheel torque.(F 538)3.1.5 effective rolling radius,nthe ratio of the linearvelocity of the wheel center of the free rolling tire in the X8direction to the spin velocity.3.1.6 free rolling tire,na loaded tire rolling withoutapplied driving or braking torque.(F 538)3.1.7 inclination angle,nof a tire,the angle between theZ8-axis and the wheel plane.(F 538)3.1.8 longitudinal force,F,nof a tire,the component ofa tire force vector in the X8 direction.F 5383.1.9 longitudinal slip velocity,L/T,nthe effective roll-ing radius multiplied by the difference between the spinvelocity(in rad/unit time)of a driven or braked tire and that ofa free rolling tire when each is traveling in a straight line.F 5383.1.10 slip angle,nof a tire,the angle between the X8-axisand direction of travel of the center of tire contact.(F 538)3.1.11 spin axis,nof a wheel,the axis of rotation of awheel.(F 538)3.1.12 spin velocity,nthe angular velocity of the wheelabout its spin axis.3.1.13 test run,na single pass of a loaded tire over a giventest surface.F 5383.1.14 tire-axis system,nthe origin of the tire-axis systemis the center of the tire contact.The X8 axis is the intersectionof the wheel plane and the road plane with a positive directionforward.The Z8 axis is perpendicular to the road plane with apositive direction downward.The Y8 axis is in the road plane,its direction being chosen to make the axis system orthogonaland right-hand.3.1.14.1 DiscussionSee Fig.1.F 5383.1.15 tire forces,F,nthe external forces acting on a tireby the road.F 5383.1.16 vertical load,nthe normal reaction of the tire onthe road which is equal to the negative of the normal force.F 5381This test method is under the jurisdiction ofASTM Committee F-9 on Tires andis the direct responsibility of Subcommittee F09.20 on Vehicular Testing.Current edition approved Oct.10,1998.Published January 1999.Originallypublished as F 424 75.Last previous edition F 424 86(1993).2Annual Book of ASTM Standards,Vol 04.03.3Annual Book of ASTM Standards,Vol 09.02.1Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United States.4.Summary of Test Method4.1 This test method is conducted by towing a dynamometervehicle behind the test vehicle moving in a straight line andgradually increasing the draw bar pull force by increasing thethrottle setting of the test vehicle to compensate for brakeapplication on the dynamometer vehicle.The dynamometerbrake application is to be increased only as much as isnecessary to maintain a constant test speed.The test progresseswith increased throttle setting and dynamometer brake appli-cation until spinning of the test tires occurs.4.2 The recommended vehicle test speed is 2.5 to 7 mph(4to 10 km/h).4.3 The test may be conducted utilizing a single-wheeldriving traction truck or other specialized vehicles utilizing anindependently loaded and driven test wheel position.Adescrip-tion of these specialized test vehicles and their appropriate testprocedures are not detailed in this test method.5.Signifi