I had a weird mechanical on my fixd gear. I was pushing hard going up a little hill when I suddenly stopped. The drive side bolt appeard to have slipped, and the wheel toed in and rubbed the chainstay and promptly stopped. I quickly got off the bike to retighten the bolt and as I straightened out the wheel, a piece of metal fell out from next to the axle bolt. I picked it up and realized it was about 3/8 of a nut. Somehow, my guess is possible overtightening coupled with aggressive riding put a lot of stress on the nut on the inside of the chainstay. There was enough of the nut still there to hold the wheel, so I tightenend it and rode home—very carefully and slowly. When I got home, I took the wheel off and the rest of the nut fell off. I guess I am a little concerned because I have never even heard of this happening to anyone. I have ridden that wheel on the bike for about 18,000 miles over the last 5 years. I ride the fixed gear hard. It has a 48x17 on it and I push the hills—and I have ridden it on a lot of hills- including Independence Pass (from the Aspen side) in Colorado. I have always liked this bike because mechanically there is very little that can go wrong.

I wonder if anyone else has had a similar breakdown.

Train safe-

It's the locknut.Some break easily when overtightened.I've broken a couple on formula hubs.No biggie,it happens.

I'm having a hard time visualizing what broke here...

Although it's not happened to me, I've seen this failure documented several times on this forum and elsewhere. What broke is the hub bearing locknut, and some designs are weak and can eventually break due to fatigue. I suggest you find a nut that is wider and thicker to replace it.

thanks-- that's what I figured. I will replace it with a wider and thicker locknut-

train safe-