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An improvement of coast down method used for vehicle tire rolling resistance determination at drum benches is described. The method is based on the discovered differential equation solution in form of explicit function “time-distance” for deceleration motion of mechanical system. This solution conforms with the partial solution of Rikkati equation [1]. It eliminates the traditional necessity to find values of the speed as parameter of indirect measuring which contains several sources of error. This simplifies required measurement instruments. A simple but highly accurate way of measuring the inertia moment of rotating bodies, free from the mass limitations, is proposed as an important part of the new method. It does not require a dismounting the rotating bodies and removing them from their supports. Examples showing the new method accuracy, repeatability and reproducibility are presented.

The differential equation of motion of a freely coasting vehicle is analysed and its integral solution in the form of an explicit speed-time function and then a distance-time one is derived. The latter form eliminates the traditional speed term from the equation. By making speed or deceleration measurements unnecessary, a whole set of potential error sources is eliminated, thus improving the sensivity and accuracy of the coast down method. By replacing the distance measurements with precision test track markings, the coasting data requirements are reduced to accurate measurements of time only. This simplifies both the method and the test facility, and improves the reliability of the test data. Because of the efficiency of this a significant volume of test data has been gathered, and included in this report, which characterizes vehicle aerodynamic drag and rolling resistance.