How do spiral arm contrasts relate to bars, disk breaks and other
  fundamental galaxy properties?
  We investigate how the properties of spiral arms relate to other fundamental
galaxy properties, including bars and disc breaks. We use previously published
measurements of those properties, and our own measurements of arm and bar
contrasts for a large sample of galaxies, using $3.6 \mathrm{\mu m}$ images
from the Spitzer Survey of Stellar Structure in Galaxies (S4G). Flocculent
galaxies are clearly distinguished from other spiral arm classes, especially by
their lower stellar mass and surface density. Multi-armed and grand-design
galaxies are similar in most of their fundamental parameters, excluding some
bar properties and the bulge-to-total ratio. Based on these results, we revisit
the sequence of spiral arm classes, and discuss classical bulges as a necessary
condition for standing spiral wave modes in grand-design galaxies. We find a
strong correlation between bulge-to-total ratio and bar contrast, and a weaker
correlation between arm and bar contrasts. Barred and unbarred galaxies exhibit
similar arm contrasts, but the highest arm contrasts are found exclusively in
barred galaxies. Interestingly, the bar contrast, and its increase from
flocculent to grand-design galaxies, is systematically more significant than
that of the arm contrast. We corroborate previous findings concerning a
connection between bars and disc breaks. In particular, in grand-design
galaxies the bar contrast correlates with the normalised disc break radius.
This does not hold for other spiral arm classes or the arm contrast. Our
measurements of arm and bar contrast and radial contrast profiles are publicly
available.
