  We have used Spitzer images of a sample of 68 barred spiral galaxies in the
local universe to make systematic measurements of bar length and bar strength.
We combine these with precise determinations of the corotation radii associated
with the bars, taken from our previous study which used the phase change from
radial inflow to radial outflow of gas at corotation, based on high resolution
two-dimensional velocity fields in H{\alpha} taken with a Fabry-P\'erot
spectrometer. After presenting the histograms of the derived bar parameters, we
study their dependence on the galaxy morphological type and on the total
stellar mass of the host galaxy, and then produce a set of parametric plots.
These include the bar pattern speed versus bar length, the pattern speed
normalized with the characteristic pattern speed of the outer disk versus the
bar strength, and the normalized pattern speed versus R, the ratio of
corotation radius to bar length. To provide guide-lines for our interpretation
we used a recently published simulations, including disk and dark matter halo
components. Our most striking conclusion is that bars with values of R < 1.4,
previously considered dynamically fast rotators, can be among the slowest
rotators both in absolute terms and when their pattern speeds are normalized.
The simulations confirm that this is because as the bars are braked they can
grow longer more quickly than the outward drift of the corotation radius. We
conclude that dark matter halos have indeed slowed down the rotation of bars on
Gyr timescales.
