  We analyse the properties of a sample of 22 bright isolated spiral galaxies
on the basis of Johnson B,V,I images and optical rotation curves. The fraction
of early morphological types in our sample of isolated galaxies (or in other
samples of non-interacting spiral galaxies) appears to be smaller than in
samples including interacting systems. The overall morphological aspect is
regular and symmetric, but all the galaxies present non-axisymmetric components
in the form of bars or rings. We find that the color indices become bluer
towards the outer parts and that the ir central values are well correlated with
the total colors. The properties of the bulges span a larger range than those
of the disks, that thus are more alike between them. None of the galaxies shows
a truncated, type II disk profile. It is found that the relation between
surface brightness and size for the bulges, the Kormendy relation, is tighter
when only isolated galaxies are considered. We find a similar relation for the
disk parameters with an unprecedented low scatter. A Principal Component
Analysis of the measured parameters shows that 2 eigenvectors suffice to
explain more than 95% of the total variance. These are, as found for other
samples including spiral galaxies in different environmental situations, a
scale parameter given by the mass or, equivalently, the luminosity or the size;
and a form parameter given by the bulge to disk luminosity ratio, B/D, or,
equivalently, by the gradient of the solid-body rotation region of the rotation
curve, the G-parameter. We report here a tight correlation between G and B/D
for our sample of isolated spirals that could be used as a new distance
indicator.
