  We study the dynamic behaviour of 1D spring-block models of friction when the
external loading is applied from a side, and not on all blocks like in the
classical Burridge-Knopoff-like models. Such a change in the loading yields
specific difficulties, both from numerical and physical viewpoints. To address
some of these difficulties and clarify the precise role of a series of model
parameters, we start with the minimalistic model by Maegawa et al. (Tribol.
Lett. 38, 313, 2010) which was proposed to reproduce their experiments about
precursors to frictional sliding in the stick-slip regime. By successively
adding (i) an internal viscosity, (ii) an interfacial stiffness and (iii) an
initial tangential force distribution at the interface, we manage to (i) avoid
the model's unphysical stress fluctuations, (ii) avoid its unphysical
dependence on the spatial resolution and (iii) improve its agreement with the
experimental results, respectively. Based on the behaviour of this improved 1D
model, we develop an analytical prediction for the length of precursors as a
function of the applied tangential load. We also discuss the relationship
between the microscopic and macroscopic friction coefficients in the model.
