Tire-Road Contact Stiffness

When a rubber block is squeezed against a nominal flat but rough surface, the rubber bottom surface will penetrate into the substrate roughness profile. The relation between penetration depth w (or the average interfacial separation (u) over bar) and the applied squeezing pressure p determines the (perpendicular) contact stiffness K - dp/dw - -dp/d (u) over bar, which is important for many applications. We have measured the relation between p and (u) over bar for a rubber block squeezed against 28 different concrete and asphalt road surfaces. We find a linear relation between logp and (u) over bar, in agreement with theory predictions. The measured stiffness values correlate rather well with the theory prediction.