  We point out that at future hadron colliders the ratio of cross sections for
$pp\to Z'\to \ell^+\ell^-$ in two rapidity bins is a useful probe of the
relative couplings of the $Z'$ to $u$ and $d$ quarks. Combined with the
forward-backward asymmetry, the rare decay modes $Z'\to W \ell\nu_\ell$, and
three associated productions $pp\to Z'V$ ($V=Z,W,\gamma$), and assuming
inter-family universality, small $Z-Z'$ mixing, and the $Z'$ charge commuting
with the $SU_{2L}$ generators, three out of four normalized couplings could be
extracted. An analysis of the statistical uncertainties expected for the above
probes at the LHC for typical models with $M_{Z'}\simeq1$ TeV shows that one
lepton coupling and two combinations of quark couplings could be determined to
around 5\%, 20\%, and 30\%, respectively. This allows for a clear distinction
between models.
