  We investigate the production of the weak bosons $W^+$, $W^-$ and $Z$ at the
LHC as a function of their rapidity, reconstructed {\it experimentally} from
their leptonic decay. We show that the measurements provide a powerful tool for
constraining the parton distribution functions, as was already the case for the
lower energy $p\bar{p}$ collider data. We study the charge asymmetry
determining the $u$ and $d$ distribution functions using the reconstructed
$W^+$, $W^-$ rapidities. We also show how the ratio of the $W$ and $Z$ boson
rapidity distributions directly probes the charm quark distribution function of
the proton.
