Soft substrates are deformed by liquid-vapor surface tension upon contact with liquid droplets, forming the well-known wetting ridge. This ridge dynamically propagates with the moving contact line and critically influences liquid spreading. Here, we experimentally investigate gravity-driven sliding dynamics of water droplets on vertically tilted silicone layers whose viscoleasticity is characterized by the Chasset-Thirion model with the exponent $m$. At low Bond numbers, the sliding velocity scales with droplet size as $V_S\sim D^{\frac{2}{m}}$. While in the thin-film limit, velocity exhibits a pronounced power-law dependence on nominal substrate thickness, $V_S\sim \mathrm{\Pi }{\left(h\right)}^{-\frac{1}{m}}$. We rationalize these observations by quantifying viscoelastic dissipation within the soft layer and balancing it against the gravitational driving force using an energy-conservation framework. Our findings offer avenues for designing advanced soft coatings, anti-fouling and self-cleaning surfaces, and biomedical devices.

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• Contact line dynamics
• Drops & bubbles
• Surface tension effects
• Wetting