The mechanical loss spectrum of a yellow gold bi-crystal is presented and analyzed in detail. The relaxation strength is monitored as a function of several geometrical parameters such as sample width, length and thickness. It is found that the relaxation strength is proportional to the GB density (the inverse width), whereas it depends linearly on the sample thickness. The experimental findings are compared to finite elements (FE) simulations, where the material can glide frictionless along the grain boundary. The simulations show the same dependencies as the mechanical loss measurements. The relaxation peak in the loss spectrum can be interpreted as due to GB sliding accommodated by the elastic deformation of the grains. (C) 2015 Elsevier B.V. All rights reserved.