Evolution of the tidal torque constant E₂ (bottom panel), radius of the convective core (middle) and the quantity for solar composition models of mass M = 2, 2.5, 3.0, 4.0, 5.0, 7.0 10, 15 and 20 M_⊙ as a function of the normalised main sequence lifetime. In each panel, the highest mass track corresponds to the top curve. In the lower panel, the solid lines on the upper right corner indicate the (constant) values of E₂ for each mass as provided by Eq. (51).