  We study gaseous outflows from disc galaxies driven by radiation pressure on
dust grains. We include the effect of bulge and dark matter halo and show that
the existence of such an outflow implies a maximum value of disc mass-to-light
ratio. We show that the terminal wind speed is proportional to the disc
rotation speed in the limit of a cold gaseous outflow, and that in general
there is a contribution from the gas sound speed. Using the mean opacity of
dust grains and the evolution of the luminosity of a simple stellar population,
we then show that the ratio of the wind terminal speed ($v_\infty$) to the
galaxy rotation speed ($v_c$) ranges between $2 \hbox{--} 3$ for a period of
$\sim 10$ Myr after a burst of star formation, after which it rapidly decays.
This result is independent of any free parameter and depends only on the
luminosity of the stellar population and on the relation between disc and dark
matter halo parameters. We briefly discuss the possible implications of our
results.
