  We have studied the relationship between the solar-wind speed $[V]$ and the
coronal magnetic-field properties (a flux expansion factor [$f$] and
photospheric magnetic-field strength [$B_{\mathrm{S}}$]) at all latitudes using
data of interplanetary scintillation and solar magnetic field obtained for 24
years from 1986 to 2009. Using a cross-correlation analyses, we verified that
$V$ is inversely proportional to $f$ and found that $V$ tends to increase with
$B_{\mathrm{S}}$ if $f$ is the same. As a consequence, we find that $V$ has
extremely good linear correlation with $B_{\mathrm{S}}/f$. However, this linear
relation of $V$ and $B_{\mathrm{S}}/f$ cannot be used for predicting the
solar-wind velocity without information on the solar-wind mass flux. We discuss
why the inverse relation between $V$ and $f$ has been successfully used for
solar-wind velocity prediction, even though it does not explicitly include the
mass flux and magnetic-field strength, which are important physical parameters
for solar-wind acceleration.
