  A strong bar rotating within a massive halo should lose angular momentum to
the halo through dynamical friction, as predicted by Weinberg. We have
conducted fully self-consistent, numerical simulations of barred galaxy models
with a live halo population and find that bars are indeed braked very rapidly.
Specifically, we find that the bar slows sufficiently within a few rotation
periods that the distance from the centre to co-rotation is more than twice the
semi-major axis of the bar. Observational evidence (meagre) for bar pattern
speeds seems to suggest that this ratio typically lies between 1.2 to 1.5 in
real galaxies. We consider, a number of possible explanations for this
discrepancy between theoretical prediction and observation, and conclude that
no conventional alternative seems able to account for it.
