  We have explored the hypothesis that the total mass-ratio of the two main
galaxies of the Local Group: Andromeda Galaxy(M31) and the Milky Way (MW) can
be constrained measuring the tidal force induced by the surrounding mass
distribution, M31 included, on the MW. We argue that the total mass-ratio
between the two groups can be approximated, at least qualitatively, finding the
tidal radius where the internal binding force of the MW balances the external
tidal force acting on it. Since M31 is the massive tidal perturber of the local
environment, we have used a wide range of M31 to MW mass-ratio combinations to
compute the corresponding tidal radii. Of them, only few match the distance of
the zero-tidal shell i.e. the shell identified observationally by the outermost
dwarf galaxies which do not show any sign of tidal effects. This is the key to
constrain the best mass-ratio interval of the two galaxies. Our results favour
a solution where the mass-ratio ranges from 2 to 3 implying a massive
predominance of M31.
