Pedal ratio, or mechanical leverage is the ratio calculated from the length from the pivot point of the pedal to the centre of the foot pedal (A), divided by the length from the pivot point to the master cylinder push rod (B). Refer to the figures below.

Mechanical leverage is simply a means of increasing the brake force without increasing your leg effort. As 'A' gets longer and 'B' gets shorter, the mechanical leverage increases brake force without pushing harder on the pedal. The disadvantage is that the pedal stroke also increases, requiring you to push the pedal further.

With a 1" master cylinder stroke, a 100 pound push on the pedal, and the pedal having a 4:1 ratio, the force is 4 x 100 = 400 pounds, and the stroke is 4 x 1 = 4". With a 100 pound push on the pedal, and the pedal having a 6:1 ratio, the force is 6 x 100 = 600 pounds, and the stroke is 6 x 1 = 6".