  We explore the relative importance of the stellar mass density as compared to
the inner dark halo, for the observed gas kinematics thoughout the disks of
spiral galaxies. We perform hydrodynamical simulations of the gas flow in a
sequence of potentials with varying the stellar contribution to the total
potential. The stellar portion of the potential was derived empirically from
K-band photometry. The output of the simulations - namely the gas density and
the gas velocity field - are then compared to the observed spiral arm
morphology and the H-alpha gas kinematics. We solve for the best matching
spiral pattern speed and draw conclusions on how massive the stellar disk can
be at most. For the case of the galaxy NGC 4254 (Messier 99) we demonstrate
that the prominent spiral arms of the stellar component would overpredict the
non-circular gas motions unless an axisymmetric dark halo component adds
significantly in the radial range R_exp < R < 3*R_exp.
