  We test the theoretical prediction that the straightest dust lanes in bars
are found in strongly barred galaxies, or more specifically, that the degree of
curvature of the dust lanes is inversely proportional to the strength of the
bar. The test used archival images of barred galaxies for which a reliable
non-axisymmetric torque parameter (Qb) and the radius at which Qb has been
measured (r(Qb)) have been published in the literature. Our results confirm the
theoretical prediction but show a large spread that cannot be accounted for by
measurement errors. We simulate 238 galaxies with different bar and bulge
parameters in order to investigate the origin of the spread in the dust lane
curvature versus Qb relation. From these simulations, we conclude that the
spread is greatly reduced when describing the bar strength as a linear
combination of the bar parameters Qb and the quotient of the major and minor
axis of the bar, a/b. Thus we conclude that the dust lane curvature is
predominantly determined by the parameters of the bar.
