I took my 2 year old Scott department store bike out for a mud ride yesterday. Towards the end of the ride I noticed the my rear brake was extremely soft. During the ride the rear brake had been real sweet cause I had just adjusted it. This morning I look at the rear pads and they are almost entirely worn down. Before I rode that had at least half left. They nearly crumbled right away. Any idea why this happened? The front brake seems fine.