(a) v_c as a function of motor stiffness k_m for different ratio R = Δz/b when ω_on = 40 s⁻¹, where Δz is the width of the nonzero range of ω_off, and b is the width of the uphill region of the saw-tooth potential W₁ (see Fig. 1). (b) v_c as a function of ω_on for different motor stiffness k_m when R = 0.1. The other parameters are the same as those in Fig. 2.