  We consider transient random walks in random environment on Z in the positive
speed (ballistic) and critical zero speed regimes. A classical result of
Kesten, Kozlov and Spitzer proves that the hitting time of level $n$, after
proper centering and normalization, converges to a completely asymmetric stable
distribution, but does not describe its scale parameter. Following a previous
article by three of the authors, where the (non-critical) zero speed case was
dealt with, we give a new proof of this result in the subdiffusive case that
provides a complete description of the limit law. The case of Dirichlet
environment turns out to be remarkably explicit.
