Photospheric radius evolution for the 20 SDSS SNe Ib/c from the BB fits on the griz SEDs. Discovery epochs are marked by red dashed lines, the last non-detections by dashed blue lines. The epoch of the first spectrum is marked by a black segment. Here we include host-extinction corrections. The vertical green line indicates the explosion date as derived from the best PL fit (, see Sect. 3.4.1) on the prepeak BB radii, which is shown with a green solid line. The PL-derived explosion dates show that most of the SNe were discovered at early epochs, when the photospheric radius was remarkably small, and thus that the ⁵⁶Ni is likely to be present in the outer layers for most of them (see Fig. 1 in PN13 and Sect. 3.4.4). The vertical magenta line indicates the minimum explosion day t_min computed from the spectral velocities (see Sect. 3.4.1). Both t_min and maximum luminosity epochs are marked by black vertical dashed lines. Blue, red, and magenta labels correspond to SNe Ib, Ic, and Ic-BL, respectively.