An experiment was conducted in which a specially instrumented Volvo 242 car was run at 50, 60, and 70 km/h over 20 road surfaces with various textures. Macro- and megatexture as well as the shorter wavelengths of unevenness were measured by a mobile laser profilometer, the signal of which was analyzed to obtain the texture profile spectrum for each surface in the 2- to 3500-mm texture wavelength range.
The fuel-consumption data at each speed and averaged for the three speeds were regressed on the texture profile spectrum data. The results show (1) Fuel consumption varies over a range of approximately 11% from the smoothest to the roughest road tested if texture wavelengths in the range 0.6 to 3.5 m are considered, and approximately 7% if texture wavelengths in the range 2 to 50 mm (macrotexture) are considered. (2) The correlation between fuel consumption and texture is as high as 0.90 (correlation coefficient) in the range 0.6 to 3.5 m and reduces smoothly at shorter wavelengths, down to about 0.60 at wavelengths equal to common maximum chipping sizes on roads. Thus it appears that fuel consumption is influenced very much by road unevenness and megatexture, but somewhat less by macrotexture. (3) Some of the mega- and macrotexture influence is due to a covariation with shortwave unevenness, and the pure effects of each, especially macrotexture, are somewhat less than noted in (1) and (2). (4) The results indicate that significant parts of the losses may occur at frequencies typical of vehicle body and wheel hop resonances and, thus, be dissipated in the car suspension system. (5) The results demonstrate that the road surface quality has a great impact on car fuel consumption, and that the largest potential for improvements may be to control megatexture and, most of all, shortwave unevenness on roads. Also macrotexture is important to control, at least when car speeds of 60 to 70 km/h are common. The unevenness at longer wavelengths has not been covered in this experiment.