Spiral galaxies’ disks are usually considered to be dominated by massive dark matter halos when the extended rotation curve, V, is flat. We derive disk surface density as a function of radius, for variable V, density wave arm pitch, i, and multiplicity, m. For a galaxy with a flat V, we derive a disk parameter, FD = 4 tan i / m, relative to 100% halo mass over the density wage region. The actual halo to 100% halo, FH = 1 - FD. For our example of flat curve spiral galaxies, we calculate FD which ranges from FD very much less than 1 for the almost all halo for tight-armed NGC 7217 to FD ≈ 1 for the almost all disk in loose-armed, NGC 3198. Our examples challenge the commonly accepted dominance of halos over all spiral galaxy disks.