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¯) and the applied squeezing pressure p determines the (perpendicular) contact stiffness K = dp/dw = -dp/du¯, which is important for many applications. We have measured the relation between p and u¯ for a rubber block squeezed against 28 different concrete and asphalt road surfaces. We find a linear relation between logp and u¯, in agreement with theory predictions. The measured stiffness values correlate rather well with the theory prediction.