A unique “quarter-car” trailer has been designed and built at the Belgian Road Research Center for measuring the rolling resistance of a reference tire on the road. Its design and performances are briefly outlined. It has been used for investigating the influence of road-surface characteristics on the rolling drag experienced by a car tire. On a wide variety of surface types and conditions on dry paved roads, the coefficient of rolling resistance ranges between 0.013 and 0.021. In terms of fuel consumption, this can be converted into 9% relative influence of the road surface. With respect to the intrinsic tire rolling resistance coefficient (0.010) as measured on a particularly smooth and even test track, the worst road surface can double the rolling resistance. The main surface-related influencing factor has been found to be surface profile irregularities in a wavelength range lying between macrotexture and un-evenness, namely megatexture (50 mm < wavelengths < 500 mm), which had already been reported as responsible for tire/road noise.

The results of an analysis of the transverse profile measurement data collected in the FILTER Experiment are presented. The purpose of the analysis was to determine the repeatabilities, reproducibilities, and accuracies of the measurements. Application of the International Organization for Standardization 5725 standard resulted in the detection of a significant proportion of outlying results with most if not all devices. After removal of the outliers, average standard deviations ( SDs) for repeatability were typically 0.1 percent for cross fall, 0.5 to 0.9 mm for rut depth, and 0.25 mm for water depth: cross-fall measurements exhibited an average SD for reproducibility of 0.5 percent; for rut depth measurements the values were 1.7 to 2.7 mm, and for water depth measurements the values were 2.1 to 2.2 mm. The overall SD for the accuracies of the profile measurements was found to be 1.9 mm. The rather wide range of (in)accuracy (0.8 to 3.2 mm) among the different test sections is explained by the influence of longitudinal unevenness (international roughness index). Operating speed in the speed range used in the experiment had no significant influence on most measurements obtained. Moreover, speed had no significant influence on the repeatabilities or the reproducibilities of the indices or on profile measurement accuracy. Averaging distance had a significant influence on the SD for repeatability, which decreased by a factor of 2 to 4 when the averaging distance increased from 50 to 500 m. The reproducibilities of the indices did not significantly depend on the averaging distance in any systematic way.

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