Evolution of equatorial rotational velocity v_rot (thick dot-dashed), critical velocity v_crit (dashed), and the critical velocity fraction v_rot/v_crit (solid red) for 5 M_⊙ (panels a, b), 15 M_⊙ (panels c, d), and 25 M_⊙ (panels e, f) models at MW metallicity (panels a, c, e) and SMC metallicity (panels b, d, f). The initial critical velocity fraction values are all approximately 0.6. The X-axis indicates the fractional main sequence lifetime, t/t_MS.