We've gotten some serious snow in Montreal lately and it was snowing today so I decided to take the fixie out for a little fun. While I was riding through a particularly bumpy patch of snow, I tried a little whip skid, just for kicks and giggles. Lo and behold, my chain fell off. Luckily I wasn't going too fast and I don't ride brakeless. I was able to hook the chain on the top of the chain ring and peddle it back on. The tension was certainly adequate - there was no discernible play in the chain. The cog and lockring are secure. After I got home I took off the chain and discovered that the chainring was the slightest bit loose. With the chain on I couldn't detect any play at all. What's the deal? Cog doesn't look that worn out?

you have your answer. a sufficiently loose chanring will throw a chain.

btw, replace your lockring. what you've got on right now sucks. even really good ones are cheap, no need to skimp on this.

I'd say if you were able to "hook the chain on the top of the chain ring and peddle it back on", your chain is way too loose.

What makes one lockring better than another? I'm just curious because I have those lockrings since those are what my LBS carry.

Machining of the threads. You have an AL formula lockring. They are fine.

If you were able to put the chain back on your bike without moving your rear wheel then the chain tension was obviously way too loose.

Yeah, I'm curious as to how you can remount the chain without there being any play.

Remounting the chain by pedaling it back on is really bad for your chainring and chain. If there is any tension whatsoever, you may bend a tooth or two on the chainring and/or loosen up/bend some chain links.

Also, check your chainline. If it's not straight, even with the proper tension, you can take remove the chain pretty easily.

Exaaactly.

I really want to see pictures of this finely tuned machine now though

I pedal mine back on all the time. No harm no foul. I figure road bike chainrings have that happen all the time. It's called shifting.

I hope you are joking. On a road bike, the derailleur rather gently takes up the tension of the chain--- allowing it to shift easily. They also have ramps to promote shifting, and the teeth are not cut uniformly for a reason.

I have found that chainline is far more important than chain tension when it comes to throwing chains. The wobbly chainring will definitely ensure that you are not keeping a good chainline. A drivetrain with a properly set chainline can have a droopy chain that will never be thrown while an improperly set chainline will cause the chain to hop off no matter how tight the chain is tensioned. And it is actually much better for drivetrain components to run the chain sorta on the loose side.

They don't do it under tension like you would with a ss/fixed wheel. You are putting lots of force on the chain (I've bent a chain and a chainring doing this). I wouldn't trust your chain for a second if you do this "all the time".

I'm joking about it being harmless, but I do it sometimes when I don't have a wrench on me and there is no other option. It's always done with teeth gritted and prayers to Mardok that I don't break a tooth.

this

I rounded the notches out on one of these the first, & only time, I took one off of a wheelset I bought. I'm pretty sure if i tried, I could bend it with my bare hands. That's not a component I'd want to rely on. plus, an aluminum lockring sounds like and accident waiting to happen.

Considering how and where the force is exerted on a lockring, I can't see any reliability problem with aluminum. The hub threads are aluminum and take a lot more stress. The notches are indeed easier to round off, but I wouldn't bother replacing it until/unless that happens.

even with grease, wouldn't an aluminum lockring stand a greater chance of seizing onto a hub? 2 metals of the same type sharing a contact surface and all that?

I don't think my chain was too loose. With the bike standing still (as in a trackstand or whatever), there was almost no discernible play in the chain when applying pressure to the cranks. The chainline is also perfectly straight.

I just looked at the chainring - no defects. In light of what ianjk said, it's obviously better to install the chain the proper way but I was two miles from home without tools. I disagree, Scrodzilla.. It may not be good for it, but it's possible. Only the top of the chain is in tension when you peddle forward. The lower portion of the chain just hangs loose until you peddle it all the way around.

It seems pretty obvious that the loose chainring did it. I'll be keeping a closer eye on it.
thanks everyone.

There ya go. Attached is a picture of the drivetrain right I peddled the chain back on. thanks for the help man

I know this is off topic but there's been a lot of talk within this thread about aluminum Formula lockrings. What about Formula lockrings that are made of steel? Are those crappy too? I ask because I just picked one up from a local shop for a bike I'm currently building. It doesn't seem like it would be problematic by looking at it but I haven't installed it yet.

Dissimilar metals are prone to seizing. The difference in conductivity causes oxides to tend to form at the junction.

The word "peddle" refers to going around selling something. "Pedal" is the bike part, and you make a bike go by pedaling.

Heck, my road bike chain has almost no discernible play when you do the same thing. I don't think that's the way you are supposed to check it. What kind of slack do you have without applying pressure to the cranks?

LOL, @ all the "chain was too loose" ... all yous kids, better not be the ones with the loud arse grinding and poping chains .

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I don't get it. A road bike has infinite play. The cranks spin backwards freely at a stop. On a fixed bike it doesn't, but if it has some slop in the middle at the tightest point the chain is too loose. I guess I could see what you mean if you're just feeling whether the chain can wiggle up and down, but that's not what the OP meant.

If you apply forward pressure on the crank and don't let the rear wheel turn, the chain (the top section, anyway) will be "tight" on any bike. I assumed that was what the OP meant by "almost no discernible play in the chain".