Ttkc wrote:
Thanks- The chain came off and prevented the pedal from turning. I do not know exactly how or why. The bike got picked up and the chain moved around after so I cannot see how it ended up. It did not break. It seems like it went over the right side of the gear because the bike is now in my garage with the chain still off in that position on the right/outside of the gear.
Did it just stop the pedal from turning or did it cause the rear wheel to stop? If it's the pedal then I've had this happen a few times, but it shouldn't lead to a crash. I guess if you were pedalling really aggressively then the force of your legs could cause a crash and/or the shock of your pedals seizing up could cause you to tense up and lose control. But in my experience this tends to happen when I'm on a very bumpy surface and freewheeling - it's the lack of tension on the chain that enables it to jump off. If I'm pedalling then unless I'm also trying to shift then the chain should be under tension and can't jump off. I guess maybe you got very unlucky with the timing - e.g. stopped pedalling for a rough section, then hit the pedals hard again without realising the chain had jumped.
If it's the wheel seizing up that's a totally different matter and at 19+mph a crash is pretty much inevitable unless you're an experienced fixie rider who can pull off a hell of a rear wheel skid! But if that was the case I'd have expected the chain to jump left into the spokes/hub, not right. And at that speed I'd also expect your spokes/hub to be seriously damaged.