  We determine the parameters of scaling relations analogous to the Fundamental
Plane of elliptical galaxies for the bulges and disks of a sample of 40 spiral
galaxies. To this end we derive structural parameters (scalelengths and surface
brightnesses) from near infrared H band images, and kinematical parameters
(rotational velocities) from optical rotation curves. In the case of the disks,
we test the accuracy of the derived relation as a distance indicator by
comparing its scatter to that of the H band Tully-Fisher relation for the same
sample, and find that the accuracy attained by the latter is slightly higher
(the dispersion is 19% versus 23% for this sample). It is speculated that the
difference is due to the more robust character of global parameters, rather
than those associated with the inner parts of disks. It also apperas that (a)
either the stellar mass-to-light ratios of bulge and disk increase with the
size of the components, or (b) the bulge and disk relative contributions to the
overall rotation of the galaxy (and, as a consequence, to its total mass)
become steadily smaller with increasing size.
