While I was riding to college today, I heard a loud bang (and I've heard a few of them since i bought the bike), and immediately thought I had busted a spoke. I was running a little late, and was almost to school, so I kept going.

Get to school, then when I'm finished, I head for home. As I'm shifting, I suddenly find myself with the chain stuck between the 5th and 7th cogs. I thought that something had expanded on the cassette, so I rode (downhill) to the nearest shop in the chain that I bought the bike from. They start looking at it, and realize that I'm completely missing the entire 6th cog.

Got the bike in June, so they warrantied the replacement..

So has anybody else had an entire gear go AWOL w/o crashing the bike?

Can't even say I have ever heard of this happening before.

Was riding home one night and lost all my gears when a lock washer on a three speed hub failed... thankfully... it happened at very low speed and there was no damage to the bearings.

I don't get it. The entire cog on the cassette came off? How can this happen without taking off the outer cogs? Or did the teeth somehow strip off? Either way sounds like a freakish event and a seriously defective part.

It appears that the cog was held to the cassette as they usually are, but the supports snapped (presumably each support breaking was one of the mystery bangs), and then it snapped into at least 2 parts. I certainly didn't hear any metal hit the ground (and I don't wear headphones), so I'm going to look for the missing bits tomorrow when I go back to school.

I lost a little over half of a cog last winter. After I got home I could wiggle the remainder of the cog with a pair of pliers. My guess is that yours snapped harder then mine and ejected both pieces from the cassette. Although I was cranking on the gear that broke, where it sounds like you weren't in the gear that broke?

I was shifting when I heard the bang.

My cassette looked just like the missing area of your cassette in your photo.

Mine was an SRAM cassette, but I didn't have a receipt or anything to use to try and pursue a part return based on a manufacturing defect. Sucked, cause that cassette was only 7 months old.

Rode through the area that I suspect I lost the gear... no sign. Not that it mattered, but I would have liked to seen what it looked like.

Sounds like spontaneous combustion... of the loud variety.

I haven't had it happen, but I've seen busted cassettes on other bikes. Stuff happens.