all of a sudden, i'm throwing my chain
 

in five years of riding fixed, i've never really thrown my chain while riding (unless just screwing around while wrenching and something was way off).

in the last week, i've throw it three times. the first two times, i coasted to a stop with no problems, but tonight, it locked up my wheel and i almost went over.

i keep my bike in good shape have been riding it in its current configuration for three months with no problems. my chainline is pretty straight, so what could be going on here?

i ride my chain somewhat loose, but nowhere near too loose. maybe my chain is shot? i'll examine it closely tomorrow.

did you overcome a chain throwing problem?

does it pop off the cog or the chainring?

how long have you had that chain? I would bet its either stretched out or your teeth on your cog/chainring have worn down.

+1 on chain stretch. shine a light behind your chainring and look at how the chain sits in all of the teeth.

also, take the chain off, spin the crank and look at the space between the chainring and chainstay and make sure that it's constant thru the rotations while you're checking things out. might be a good time to adjust the chainring if it needs it.

is your entire drivetrain 1/8"?

first time i threw my chain, it was on a mixed drivetrain. 2nd time i threw it, the cheap chain was majorly stretched. i bought a chainwear gauge for a couple of bucks and check my chains every few weeks now. most likely overkill, paranoia and OCD on my part, but i don't mind.

I'd check all that was said above. Perhaps your chainring bolts are loose? That happened to me once.

I'd also check your chainstays. Could be cracked. Wasn't this similar to what Lance had a couple of tours ago when he was mashing the pedals? But then again, he only slipped in his pedals and not a thrown chain.

Or maybe you're just too damn strong and the mashing on your pedals is causing your frame to flex so much that you are throwing your chain. Or maybe not.

What kind of chainwheel do you have? If it's ramped and pinned for shifting, that could be the culprit.

i don't know if it's coming off the cog or chainring.

my chainring bolts are loc-tited in and my frame is ok, it's three months old and was cutsom build to minmize torsional twisting in the BB.

the entire drivetrain is 1/8". sugino 75 chainring, EAI cog, and a cheap KMC Z chain, which isn't very old, but suspect is the culprit.

thanks for the tip on shining the light behind the ring, visitordesign. i'll try that this afternoon and see what i find.

NEW CHAIN man, everytime I have thrown a chain it was overdue to be replaced. Also take a good look at that rear cog to make sure a tooth or two haven't worn too much

I had this happen this spring on a bike with vertical drops, a magic gear, and a very unround chainring causing a big tight spot that I just ignored. 3 months of winter riding and all of a sudden it came off (chainring) 3 times just on the way to work. Readjusted the wheel in the dropouts as a quick fix, but the chain was shot according to my chain checker.

Once the cone and locknut on my rear hub (drive side) which threw off my chainline causing my chain to drop.

i replaced my chain with a SRAM PC-1 and it's been smooth riding ever since.

this chain is actually smoother and more quiet than some $50 izumi track chains i've run.

i threw my chain on friday, and set a new record for longest skid. turns out i was pulling my hub forward under power. chain tensioners are now at the top of my list. i'm pissed about munching my spokes, too.