On my way back from lunch today, I knew I was going to be hitting a tight corner, so I prepared and hit it at about 50mph. As I'm going around this corner, my rear tire slides while I'm going through the apex. The ground was clear of any fluids, sand, dirt, and rocks... I don't know what the heck happened. About a block away, I had to make another turn (Same side -right-) going ~5mph and the rear tire slid a little again. As I pulled into my parking spot, (about a half mile away) I checked the tire and it was warm, soft, and free of any foreign substances. I'm baffled as to what the problem was. I took this picture as soon as I got off my bike... (yes, I know my rim is dirty) Any ideas?