Tire rubber treads wear patterns that are described as craters can appear in mild conditions. This article demonstrates that craters can be recreated on a laboratory tribometer, which has been developed especially for rubber filled compounds testing. A local analysis of the worn surfaces has shown that the dimension, density and location of craters are closely related to carbon black agglomerates found within compounds. The viscoelastic properties of the agglomerates have been found by carrying out nanoindentation tests: these give a Young's modulus of around 300 MPa and a elasto-plastic limit between 7% and 14%. Finally, an original system is proposed to explain the crater formation on the release of internal stresses due to an agglomerate mechanical plasticizing of the rubber surface. Electronic microscope observations and a finite element analysis show that the agglomerates are flattened by the indentor contact and tilted, to create craters on the worn surface.