Friction/water depth relationship-In situ observations and its integration in tire/road friction models

The purpose of this paper is to provide new experimental evidences about the friction/water depth relationship and to improve the formulation of friction models in terms of consideration of the effect of water depth. Tests are conducted on test tracks. Friction forces are measured by means of a dedicated trailer providing a locked-wheel (full sliding) friction coefficient. The test surfaces are wetted by an on-board wetting system providing water depths varying from 0.1 mm to 1.50 mm. Effect of the road surface texture on the friction/water depth variation is shown and commented. Inputs newly provided by field tests, compared with laboratory tests, are highlighted. The obtained friction/water depths curves are assimilated to Stribeck curves and analyses, assuming conditions of a starved lubricated contact, are conducted to determine the lubrication regimes experienced by the tire/road contact when the road surface changes from dry to wet. A new friction model is formulated using the three-zone description of the tire/road contact area. The formulation is focused on the water drainage term reflected by a so-called hydrodynamic term F-HL. It was assumed that F-HL is a product of elementary functions expressing the respective effects of water depth, speed, tire tread depth, and road surface macrotexture on water drainage. Form of the elementary functions is derived from experimental evidences and consideration of previous friction models. Fitting of the new model to experimental data is shown and comparison with previous models is discussed.