Example of a M_1,  i = 1.1 M_⊙, q_i = 0.8 and a_i = 4.1 R_⊙ binary system in which tides lead to contact. In Panel a we show the exchange between the orbital angular momentum L_orb (solid black line) and the secondary’s spin angular momentum S₂ (solid orange line), which coincides with the decrease in L_orb/(S₁ + S₂) (dashed green line). The primary’s spin angular momentum S₁ is shown with a solid blue line. Panel b shows the evolution of the moment of inertia (solid lines) and tidal synchronisation timescale (dashed lines) for both components. While the moment of inertia of the primary decreases around M₁ = 0.3 M_⊙, it sharply increases for the secondary. At the same time, the secondary star’s tidal synchronisation timescale decreases by approximately two orders of magnitude. Panel c shows the evolution of the primary’s and secondary’s radii (solid lines) and Roche lobe radii (dashed lines). While the former fills its Roche lobe, tides cause orbital shrinkage, which results in the secondary also filling its Roche lobe.