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The relative bar torques for 45 galaxies observed at $K$- band with the 4.2mWilliam Herschel Telescope are determined by transforming the lightdistributions into potentials and deriving the maximum ratios of the tangentialforces relative to the radial forces. The results are combined with the bartorques for 30 other galaxies determined from our previous $K$-band survey(Buta & Block 2001). Relative bar torques determine the degree of spiral armforcing, gas accretion, and bar evolution. They differ from other measures ofbar strength, such as the relative amplitude of the bar determinedphotometrically, because they include the bulge and other disk light thatcontributes to the radial component of the total force. If the bulge is strongand the radial forcing large, then even a prominent bar can have a relativelyweak influence on the azimuthal motions in the disk. Here we find that therelative bar torque correlates only weakly with the optical bar type listed inthe Revised Shapley-Ames and de Vaucouleurs systems. In fact, some classicallybarred galaxies have weaker relative bar torques than classically unbarredgalaxies. The optical class is a poor measure of azimuthal disk forcing for tworeasons: some infrared bars are not seen optically, and some bars with strongbulges have their azimuthal forces so strongly diluted by the average radialforce that they exert only small torques on their disks. The Hubbleclassification scheme poorly recognizes the gravitational influence of bars.Applications of our bar torque method to the high-redshift universe are brieflydiscussed.Comment: 9 pages, 9 embedded postscript figures. Accepted for publication in  A&A, May 30, 2001. Original high-quality figures can be obtained from  ftp://ftp.ing.iac.es/pub/outgoing/knapen/Block

The gravitational torque of bars in optically unbarred and barred galaxies