  The detachment of a sphere from a viscoelastic substrate is clearly a
fundamental problem. In the case viscoelastic dissipation is concentrated at
the contact edge, and the work of adhesion follows a quite popular simplified
model, Muller has suggested an approximate solution, which however is based on
an empirical observation. We revisit Muller's solution and show it leads to
very poor fitting of the actual full numerical results, particularly for the
radius of contact at pull-off, and we suggest an improved fitting of the
pull-off which works extremely well over a very wide range of withdrawing
speeds, and correctly converges to the JKR value at very low speeds.
