This study investigates rubber-road friction through a controlled experimental methodology. While models usually relate grip and real contact area to the power spectral density (PSD), surfaces with equal spectra may behave differently. To isolate morphology effects, seven 3D-printed samples were designed with identical PSDs but different height distributions, controlled via skewness and kurtosis. Their topographies were validated by profilometry, then tested on a linear friction rig under dry and lubricated conditions. Results showed up to 20% variation in total friction despite identical PSDs, proving that height distributions decisively complement PSD in friction and wear modeling.

• The limitations of relying solely on PSD in friction prediction
• Evidence of up to 20% friction variation at constant PSD
• How 3D printing enables controlled and repeatable test surfaces
• The procedure to validate artificial surfaces with profilometry
• Why height distributions affect adhesion and total friction