If the bit has a 1.5" cheek and a 4.5" lower shank, thus producing a 1:3 ratio of cheek to lower shank, while the ratio of the cheek to (upper + lower) shank is 1:4, and producing 4 pounds-force of pressure on the horse's mouth for every 1 pound-force (4 newtons per newton) placed on the reins. If the bit had 2" cheeks and 8" shank (ratio of 1:4), the bit will produce of tension for every one applied by the reins (5 N/N). Regardless of the ratio, the longer the shank, the less force is needed on the reins to provide a given amount of pressure on the mouth. So, if one were to apply of pressure on the horse's mouth, a 2" shank would need much more rein pressure than an 8" shank to provide the same effect.