Three-step cone pulleys 2 and 3 rotate about fixed axes B-B and A-A. Open belt 1 runs over opposing steps of pulleys 2 and 3. By shifting the belt from one pair of steps to another, three different transmission ratios are obtained. The radii of the steps are selected from the condition of a constant length L of the belt. This condition need not be complied with if an idler pulley is used. The transmission ratio from pulley 2 to pulley 3 is i₂₃=ω₂/ω₃=n₂/n₃= where ω₂, ω₃, n₂ and n₃ are the angular velocities and speeds (in rpm) of pulleys 2 and 3, and R2 and R₃ are the radii of the corresponding opposing steps of pulleys 2 and 3.
$SFL,BD$$