Accelerated Tire Wear under Controlled Conditions. II. Some Factors that Influence Tire Wear

Abstract

Abstract Using the test system described in (I), we have determined the effect of some of the important factors in tire wear. There are three primary factors: tire force, pavement texture, and tire surface temperature. The major factor of these three is the sustained or instantaneous tire force. Accelerometer measurements show that cornering or lateral forces are chiefly responsible for wear in contrast to longitudinal (driving and braking) forces and the test system is designed to operate on the basis of such cornering forces. The wear rate depends exponentially on tire cornering force. In the low-moderate tire force range (0–500 lbs.) this may vary from approximately 2 to 4. The exponent depends upon pavement texture, tire temperature, and tread composition. Pavement texture is important in two ways: in the actual rate of wear produced and in the influence on mechanism of wear which is reflected by the value of the above mentioned exponent. Harsh aggregate pavements produce a faster rate of wear than smoother, blunt aggregate pavements. Harsh pavements give exponents of 2.0 to 2.5 which indicate a tensile-tear mechanism; blunt pavements give exponents of 3.5 to 4.0 which indicate a fatigue mechanism. The relative rating of tread compounds can change, including outright reversals, depending upon the pavement texture. The effects of such weather factors as rain are outlined. Rain “on the pavement” lowers wear rate but the “after-effect” of rain is different. The abrasiveness of pavements after a rain increases due to chemical surface etching and this promotes increased wear until the polishing action of traffic reduces this increased abrasive character. Tire surface temperature influences absolute wear rate and compound relative rating. Our data confirm the positive temperature coefficients reported by Schalla-mach. For current tread compounds, wear rate increases approximately 2% per degree Celsius. Tread composition is important. Carbon black colloidal properties, such as structure and tint, have a marked effect on tread compound wear resistance. At low tire force these effects are minimal; at high tire force, however, high structure and tint impart significant resistance to wear. This increased resistance can be quantitatively expressed by the “Severity Index Gradient”. The correlation of accelerated test results and fleet tests is, in general, good; but, due to the overall complexity of wear behavior, tire force levels, as well as pavement texture and tire temperature, must be taken into account in correlation calculations. Otherwise, confusing results will be obtained. It is precisely this ability to vary the three primary wear factors independently that makes this particular approach to tire wear important.