For properly chosen elastomer compounds, thermorheological characterization is combined with an examination of the variation of the wet sliding friction with temperature. A conceptual argument leads to the assumption that the wet sliding friction should maximize at the energy dissipation peak associated with the dynamic softening transition at a characteristic frequency determined by the sliding speed and the effective smallest surface asperity scale. The dynamic softening transition is characterized with the peak in tan delta/G'(n) where tan 5 is the loss tangent, G' is the elastic modulus, and n is a constant between 0 and 1. The William-Landel-Ferry transform is uncritically applied for extrapolating the position of the peak in tan delta/G'(n) at high frequencies. Even based on the criterion of tan 5, the results obtained on a concrete surface indicate that the effective smallest asperity scale is of order of 100 mum. (C) 2004 Wiley Periodicals, Inc.