710630 Tire Traction Measurement on theRoad and intheLaboratory Walter Bergman, Harold R.Clemett, and Narendra J.Sheth Product Test Operations, Ford Motor Co. NUMEROUS PAPERS HAVE been published onthesubject oftiretraction andvoluminous testdata have been accumu lated (1-4)*. Many testmethods andvarious types oftest equipment andfacilities have been developed tomeasure tire traction, andanumber ofdifferent criteria have been intro duced. Most ofthetests were limited tomeasurements ina single operating mode-primarily braking-and only afewpub lications pertain tocornering orcombination cornering-brak ingtraction measurements. Duetodifferences intestmeth ods,equipment, andtestconditions, data obtained from these measurements describe strictly relative tiretraction properties atthese specific conditions andarenotsuitable fordetermina tionoftheoverall tiretraction properties. This paper examines tiretraction inabroad sense andde velops rationale bywhich onecanmeasure andevaluate the various modes oftraction applicable torealistic customer driv ingsituations (cornering, braking, anddriving**, ortheircom binations). Theneedformaintaining common operating, environmental, andtestsurface conditions isdiscussed, along with theimportance ofrelying heavily onstatistical analysis and correction techniques where testconditions cannot becontrol ledwith reasonable precision. Aconcept oftraction envelope hasbeen developed toexpress thevalues oftiretraction and testconditions inprecise quantitative terms. Atechnique has alsobeen developed tocompensate fordifferences intestcon ditions andtoevaluate tireproperties onacommon basis. Laboratory techniques compatible with tiretraction measure ments onavehicle have been developed. Good correlation has been achieved between road andlaboratory measurements and alsobetween road measurements attwodifferent testsites. Bytreating tiretraction onanoverall basis, these testmethods provide more realism interms ofcustomer usage thanconven tional approaches. CRITERIA OF TIRE-ROAD TRACTION MEASUREMENTS Inthemeasurement oftire-road traction, aswith anymea surements, itisnecessary tounderstand thebasic nature ofthe properties being measured, toestablish meaningful measure ment criteria, andtocontrol oratleast account forconditions influencing these measurements.*Numbers inparentheses designate References atendof paper. **Driving torque application toaccelerate ormaintain steady state condition. -ABSTRACT This paper gives acomprehensive analysis oftire-road trac tion, utilizing newexperimental andanalytical techniques. It introduces aconcept oftraction envelope forevaluation ofthe overall tiretraction properties inalloperating modes ona common basis. Itestablishes feasibility oflaboratory tech niques fortirewettraction measurements andshows good correlation between road andlaboratory measurements andalso between roadmeasurements ondifferent surfaces. Compara tiveevaluation between newandconventional techniques for measuring tiretraction ontheroad incornering with andwith outpower application aregiven. 2330 Downloaded from SAE International by University of Wisconsin - Madison , Saturday, September 08, 2018NATURE OF TIRE-ROAD TRACTION - Tire-road traction is an interaction between the tire and the road, resulting in re­ action forces and moments acting in the plane of the road at the tire-road interface. The reaction forces and moments re­ sult from control inputs (braking and acceleration torque and steer angle) and disturbance inputs (wind forces, road irregu­ larities, and forces due to grade of the road) or combinations of both input types. Direction and magnitude of the resultant reaction force vector and the moment is determined by these inputs. Tire-road traction properties determine the maximum limits of forces and moments which can be developed at the tire road interface at given operating and environmental condi­ tions. They also affect tire force and moment slip characteris­ tics (relationships be