I was coming down a slight ( 3 to 4 % ) hill, pedaling to catch a light that was about to turn green up ahead, when my rear wheel locked up on me. If you've ever locked the rear brake before in a panic stop, you'll recognize when it happens; the back end of the bike moves sideways in an arc. It's very particular. Anyway, this happened out of the blue, coming down the hill at 23 mph.
At this point I was sure I was going to lose some teeth. No question. The only things going through my mind were "this is going to hurt" and "I wonder how it's about to happen?"
The bike started to gradually fall to the right. I leaned to the left, like I would in a sharp turn. It came back up, but then started to dump left, and I leaned right. Then I saw that I was heading for a curb, and a telephone pole behind it. This was my answer, to how it would go down. But I skidded to a stop just before I hit the curb. I don't know whether I used the front brake or not; I didn't try to steer, though, because I had no control over the bike.
I thought I was going down, and going to hit my head, or that the bike would stop before I did, and I'd fall "through" it, injuring a leg in the frame and bars. But I walked away without a scratch.
I had been cross-chaining, big to big, and the bike shifted itself to a gear I didn't have. The chain wrapped around the hub and caught itself in a spoke, locking the wheel up. I tried to pull it out, but not dice. I locked it to a sign post, took a taxi home and got my car, and drove in. I stopped and picked up my bike, which is on the roof in the parking lot downstairs.
I think I'm going to stop at LBS on the way home and see what they'll give me in trade-in value. I just replaced the whole drive train a couple weeks ago, in what could have been a bad wreck, and it feels like it's time to part ways with this bike. I don't want to stop commuting ... but I don't want to keep riding this one, either.