Top panel: epoch of the peak (t_max) for each light curve with respect to t_max in the r band as a function of the effective wavelength of the filters in the rest frame for 15 SNe Ib/c in the SDSS sample (violet, green, red, dark yellow, and cyan represent ugriz filters). Blue, red, and magenta labels correspond to SNe Ib, Ic, and Ic-BL, respectively. Bottom panel: same as in the top panel, but t_max for each light curve and for each object is plotted with respect to the interpolated t_max at the effective wavelength of r band at redshift z = 0 (6231 Å). Three out of 15 objects (SNe 2005fk, 2005ks, 2006fe) are excluded from the fit since the interpolation to 6231 Å is not possible or reliable (e.g., for SN 2006fe, we do not have the i-band maximum epoch). The 2nd-order polynomial fit to the data (and plotted in red) corresponds to t_max(λ) − t_max(r_{z = 0}) = aλ² + bλ + c, where a = −2.47 × 10^-7, b = + 4.38 × 10^-3, c = −17.86. t_max is expressed in days and λ in Å. This fit allows predicting peak epochs in the whole optical range given a measured peak in a single band, with little uncertainty (σ = 1.3 days). Vertical dashed lines indicate the effective wavelengths for the ugriz filters.