Time evolution of the C iλ1.0693 μm velocities for the four supernovae with C i detections. Various symbols represent different objects as noted. Blue, black, and red symbols represent SNe Ia with optical light-curve decline rates in the range Δm₁₅(B) < 1.0, 1.0 < Δm₁₅(B) < 1.6, Δm₁₅(B) > 1.6, respectively. The velocities are taken from the C i velocity representing the base of the line-forming region in the best-fit SYNAPPS models. The Si iiλ0.6355 μm velocity of iPTF13ebh is also plotted for comparison.