# A Simulation of Tire Hydroplaning Based on Laser Scanning of Road Surfaces
## 4 Result Analysis
### Distribution of Dynamic Water Pressure on Different Road Surfaces  
Considering that the supporting force provided by the road surface is the source of friction between the tire and the road surface, when the dynamic water pressure caused by the water accumulation is greater than or equal to the load of the tire, it can be considered that the tire and the road surface have produced water sliding. Figure 18 shows the variation of dynamic water pressure on three kinds of roads at different speeds when driving on the water-accumulated road surface.  
Figure 17: Water flow imprints at different driving times. (**a**) The analysis time is 4.0075 s, (**b**) The analysis time is 4.0105 s, (**c**) The analysis time is 4.0150 s, (**d**) The analysis time is 4.0210 s.  
As can be seen from the figure, the common characteristics of dynamic water pressure distribution on different road surfaces are as follows:  
The dynamic water pressure is positively correlated with the thickness of the water and the driving speed. At the same speed, the dynamic water pressure increases with the increase in water thickness, and the increasing rate also gradually increases; at the same water film thickness, the dynamic water pressure increases with the increase in vehicle speed.  
Figure 18: Variation of dynamic water pressure on pavement.  
When the water film thickness is in the range of 2-8 mm, the dynamic water pressure increases more rapidly with increasing vehicle speed and water film thickness. When the water film thickness is in the range of 8-20 mm, the dynamic water pressure increases more slowly with increasing vehicle speed and water film thickness. The two patterns change at a boundary of 8 mm for the water film thickness. This is because when the water film thickness is less than 8 mm, the longitudinal tread grooves of the tire have an 8 mm drainage channel, which allows water to be discharged to both sides as it flows over the tire, resulting in a relatively slower increase in the lifting force of the water on the tire. As the water film thickness gradually exceeds 8 mm, the longitudinal tread grooves are filled with water, preventing the tire from quickly discharging water from both sides, causing the water to accumulate on the tire sidewall and leading to a sharp increase in dynamic water pressure. When the water film thickness continues to increase, although the accumulation of water increases, the change in dynamic water pressure is not significant. According to the theory derived from the literature [40], the actual formula for calculating dynamic water pressure is as follows:  
\[\mathrm{P}=\rho\frac{\mathrm{V}^{2}}{2} \tag{14}\]  
In the formula, \(\mathrm{p}\) is the maximum pressure of the tire facing the water, \(\mathrm{Pa}\); \(\mathrm{v}\) is the relative velocity of the tire and water film, \(\mathrm{m/s}\); \(\mathrm{p}\) is the water flow density, kg/m.  
From this, it can be seen that the only variable in the formula is speed, meaning the dynamic water pressure is solely related to the speed of travel [41]. However, during the conversion from pressure to dynamic water pressure, factors such as the tire contact area and the contact area between the water film and the tire must also be considered. Similarly, when converting, the impact of the road surface on dynamic water pressure must also be taken into account. Under equal conditions, the size of the dynamic water pressure is OGFC < SMA < AC for paved roads. On paved roads, vehicles can achieve the critical dynamic water pressure threshold for skidding at higher speeds and with thicker water films, providing better anti-skid performance and safety margin. In contrast, while SMA pavement shows good anti-skid performance in terms of indicators, its actual simulation results in poor anti-skid effects. The SMA pavement does not significantly alleviate dynamic water pressure, and in some cases, it may not differ much from AC pavement.