Schematic circular velocity profiles (black solid lines) of galaxies of stellar mass M_* = 3 × 10¹⁰ M_⊙, embedded in an NFW halo (red dashed curve) of virial mass M₂₀₀ = 1.4 × 10¹² M_⊙ (or, equivalently, V₂₀₀ = 155 km s⁻¹) and average concentration, c₂₀₀ = 7.6 (Ludlow et al. 2016). Different curves correspond to exponential stellar discs of varying half-mass radius. The circular velocity of the dark matter plus stars at each of the half-mass radii, V_c, e, is shown by the open circles. It is clear that V_c, e is approximately independent of r_e for galaxy radii exceeding a ‘critical’ radius (r_crit) of order ∼5 kpc. The characteristic rotation speeds of disc galaxies of given mass are thus roughly independent of radius, provided galaxy radii satisfy r_e > r_crit. Conversely, galaxies with r_e < r_crit are expected to be dominated by their stellar component, and their characteristic velocities should depend sensitively on r_e.