710091 Investigation of Tire-Road Traction Properties F. D. Smithson Proving Ground Section, General Motors Corp. F. H. Herzegh B. F. Goodrich Tire Co. EFFECTIVE EVALUATION of tire traction capabilities re­ quires careful test design and proper test equipment and pro­ cedures. None of these are of value if the road surfaces on which the tires are tested are not representative of those to which the customer is exposed or do not provide realistic delineation of improved traction capabilities. This report presents the results of a study to define road surfaces so that test surfaces used for traction evaluation provide meaningful results. DISCUSSION As stated in previous papers dealing with tire traction, a measure of traction capability is a measure of tire-surface com­ bined frictional characteristics, and the data are only meaning­ ful in terms of that combination. Comparison of different tires on a given road surface cannot necessarily be directly related to tire traction performance on a different surface, either in terms of rank order or actual differences in perfor­ mance level. To explain this statement, and to lay a foundation for the data presented herein, it is necessary to discuss briefly the phenomena of rubber-road friction. The actual mechanisms involved in the development of friction forces between rubber and road surfaces are not fully understood. Researchers in the field not only disagree as to actual mechanisms but also as to the relative importance of the known mechanisms. For those who are required to evalu­ ate or utilize tire traction capabilities, complete understanding is not of major importance as long as improvements can be made and accurately documented. It is generally known that the rubber compound in a tire tread can produce friction forces and that changes in compound will affect the traction capability. The tire tread pattern is the other major parameter affecting tire traction, since on wet roads (the primary safety- related traction area) the level of friction capability is lowered due to the presence of the contaminant, water. The efficiency of the pattern in removing water and allowing intimate rubber- road contact is of paramount importance. These two tire properties, tread compound and tread pattern, are the major ones affecting traction. Data indicate that all others, such as construction, etc., are of secondary importance, if the tires are of the same inflated dimensions, except as related to their ability to allow improve­ ments in tread compound or pattern. The level of friction forces produced by a tire and the effec­ tiveness of tire pattern are greatly affected by the road surface on which the tire is operating. Real road surfaces are of virtu- ABSTRACT Tire traction performance is dependent on both the tire de­ sign and the road surface on which the tire is operated. Mea­ surement of a tire's traction capabilities is indicative of the performance of the tire-road surface combination. Therefore, it is important that the surfaces used to evaluate tire traction capabilities react in a manner similar to those on which the tire will operate. This paper presents a method for categorizing road surface traction properties by evaluating the traction performance of road surfaces when tested with a series of special tires. Data are presented on a series of road surfaces and recommenda­ tions are made for traction test surface design. 328 Downloaded from SAE International by University of New South Wales, Saturday, August 25, 2018ally infinite variety but can be categorized into five basic classes as shown in Fig. 1 (1)*. The importance of each of the two elements (compound and pattern) on the resultant traction for each of these surface types can be generalized; real surfaces do not necessarily fall into one of these distinct classifications but are combinations of these types. T