  The tumbling pattern of a bar is the main parameter characterising its
dynamics. From numerical simulations, its evolution since bar formation is
tightly linked to the dark halo in which the bar is formed through dynamical
friction and angular momentum exchange. Observational measurements of the bar
pattern speed with redshift can restrict models of galaxy formation and bar
evolution. We aim to determine, for the first time, the bar pattern speed
evolution with redshift based on morphological measurements. We have selected a
sample of 44 low inclination ringed galaxies from the SDSS and COSMOS surveys
covering the redshift range 0 <z< 0.8 to investigate the evolution of the bar
pattern speed. We have derived morphological ratios between the deprojected
outer ring radius (R_{ring}) and the bar size (R_{bar}). This quantity is
related to the parameter {\cal R}=R_{CR}/R_{bar} used for classifiying bars in
slow and fast rotators, and allow us to investigate possible differences with
redshift. We obtain a similar distribution of $R$ at all redshifts. We do not
find any systematic effect that could be forcing this result. The results
obtained here are compatible with both, the bulk of the bar population (~70%)
being fast-rotators and no evolution of the pattern speed with redshift. We
argue that if bars are long-lasting structures, the results presented here
imply that there has not been a substantial angular momentum exchange between
the bar and halo, as predicted by numerical simulations. In consequence, this
might imply that the discs of these high surface-brightness galaxies are
maximal.
