I have a 2005 Rockhopper Comp mountain bike and noticed a noise coming from the rear wheel area. It sounded like the wheel was just rubbing on the brake pads in a certain spot. I stopped and looked at it, but it just seemed like maybe the brakes needed adjusting. So after a 2 hour ride I got home and got the bike upside down and looks closer. I tried to spin the wheel, but after 2 turns it would stop completely and abruptly by hitting the break pad on one side and wobbled something fierce. I started checking the spokes and I notice a couple very loose ones then I got to one that was totally broke off where it connects to the center of the wheel. Anyway I took it in to be fixed, but what causes spokes to break as I can't remember having any break before on me? Also how likely is it that the entire wheel will collapse in this type of situation. I had been riding down a couple long hills where you get going at least 40mph or so. Was there a chance I could have wiped out if the wheel went? Just curious thanks.