Amazing just how many brake pad shapes and designs exist. It really makes you wonder if we really need any more. Some calipers use two pad designs and some four pad designs. This is largely down to the caliper designer but the main difference between the two comes down to initial bite. The leading edge of the pad is most responsible for the initial bite and since four pad designs have two brake pad leading edges per side instead of one, they tend to have more initial bite. Even so, initial bite is just one of the qualities required from the caliper and modern technology and materials may be over taking the problem somewhat since the most recent designs seem to have gone back to two pads per caliper.