Correlations between the stellar mass of galaxies in our observational sample and disc rotation speed at the stellar half-mass radius (disc galaxies from SPARC and P+07, left-hand panel); line-of-sight velocity dispersion, averaged within the stellar half-mass radius (ellipticals from ATLAS^3D and SLACS; middle panel); and effective radius (all galaxies; right-hand panel). Circles denote ellipticals, spiral symbols denote discs. The thick wiggly curves indicate the median trend, computed in bins of stellar mass. The smooth coloured curves in the right-hand panel indicate fits to the average trends.