Wow. That was possibly the worst post I've ever read. Lets break it down:
1. SHELDON BROWN IS NOT GOD!!! I know this is blasphemy in some circles but he is fallible. Jesus why do you put so much faith in someone you have probably never met and may not even exist for all you know.

2. I have never heard that smaller cogs make jumping a chain easier and I have a strong suspicion you deduced that yourself becuase there are less teeth on a smaller cog. Having a smaller cog wuld be the least of his worries I think and how many teeth does a 15t cog engage vs a 17t? Maybe 1 less...

3. Wheelbase making a chain jump? Maybe but I doubt it.

4. Have you ever ridden a really loose chain? Going fast down a hill would be enough to throw it.

seely -

you replace your chain, cog, and chainring together if you've been riding a stretched out chain for a while, or you ride hard.

the reason being, that as a chain gradually lengthens as the pins wear, it begins to wear down the cog and chainring, because the rollers are farther apart than the distance between the teeth of the cog or chainring.

now, when you throw a brand new chain into the mix, since the sides of the teeth of the chainring/cog are worn away, they can not engage the chain as solidly. what then happens is that the chain slips off, as in your case. what can complicate this issue, is that the cog and chainring can wear asymmetrically, which means that when you replaced your chain, the worn sides of the chain and the cog could have become offset differently, increasing the chance for a throw.

1.i know sheldon brown is of course not a god. but im sure he exist.

2. i didn't deduce that myself, it only makes sense. http://www.63xc.com/wakem/wakedriv.htm it's pretty simple

3. when the chainring and the cog are closer together and the chainline isn't perfect the chain is going to travel from the chainring to the cog are sharper angles. if they are further apart and the chainline isn't perfect the chain can straighten it's self out

4. i have ridden a really loose chain, ive ridden a 42T biopace many many times fast downhill. that's still not enough to throw it off, if the chainline is good (like the OP sugested) then it would be fine as long as you can keep up.



also, he mentioned he's buying one of those shadow chains. if youv'e read sheldon's new article on chain wear, you'll know that because of their design every link on the chain will have a bigger and bigger gap, which in turn would wear out the cog faster.

+1

tru dat

Ok to answer a few questions:

1) chain is a KMC... I've had problems with them in the past but we were out of everything else
2)chain did NOT break
3) i know how to tension a chain
4) chain tension was perfect (just a hair on the tight side at the tightest spot) when we left
5) we rode around for an hour on some trails, singletrack, did some skidding/skipping to make sure all was well
6) we stopped back at the house to grab some stuff, and i doublechecked the chain, tension was still good
7) several hundred yards away from the house, the chain let go
8) upon reinstalling the chain it was a fair bit loose
9) we retensioned it and all was well ever after, the end

*the cog is a 16t dura ace 1/8th, the chain was lubed with T9 (what else is there?) chainring is a sugino 42t

As far as the semantics of stretch vs. enlongate, I use the word stretch fully realizing that most likely, a metal chain does not actually stretch, but just like I say I taco'd a wheel knowing that in fact, it did not become an actual mexican treat. Its an expression. Also, my friend's room mate was nice enough to take me out tonight and show me a few good ways to stop should this ever happen again in the future. Thanks Kevin. As far as being irresponsible going 25+ on a hill, I usually hit 40 on this hill on my roadbike with little effort so I wasn't exactly riding out of my comfort zone or anything. I'm not exactly a newb here with no handling skills.

Anyways, none of this is a big deal really, and a lot of you guys are getting far too worked up over absolutely nothing of any importance. I think everyone needs to settle down a little. More than anything, the incident was amusing to me and what I thought was an interesting story.

if everyone would just loosen their ****in chains, you would not be runnin into all these problems, ****.

edit: and by the way, I surly did not read the thread, so just loosen your ****in chain

I read the article. Like I said there's a big difference between an 11t cog (which I doubt the OP is using) and a 15 -17.

And a Biopace isn't going to produce the kinda of slack the OP was refering to.

just bought this chain beotch.

the sneaker on the rear tire is an interesting emergency brake. wedge that thing in between the rear bars.

Rode BMX like that in Jr Hi Skool. Easy with 20" wheels. To stupd to fix my break then.

I have seen this kind of "failure" quite a bit recently.

In most instances, I have determined that improper assembly is typically the culprit.

Old fashioned chains had thick plates, with considerably more central pin bearing surface, that were more forgiving when utilizing a standard chain tool.

Modern chains typically have very thin sideplates that are much more sensitive to proper assembly. If you assemble the chain in the conventional manner, and end up creating a larger than factory specified gap between the plates and the central (inside) link, under heavy pressure, the chains quite simply pull apart.

Improper assembly can also shear a crescent shaped sliver of sideplate (via pin push) that will guarantee failure eventually.

The cure? Carefully assemble the chain with a conventional chain tool, then measure the plate span at the connection, or induce a "stiff link" condition, and institute local deflection manually to open it up, or the best yet, get a chain that has a "master link" system (Wipperman etc.) that will not allow operator error in installation. There is a reason a lot of chain manufacturers have this feature.

BTW, if you did use a "master link" style, and did not Malachi anything else...............the chain was too tight.

This seems like the most likely scenario mentioned so far. I am extremely confident that there is no way a brand new chain, even the crappiest one in existence, would stretch enough to cause it to fly of after one day of riding. This just doesn't happen unless the chain is horribly defective. Chains break, they wear out, they slip off of gears, they fail to mesh with worn-out gears, but they do not ever spontaneously elongate by an inch over a day's use, which is what would be required for this to happen.

OP, when was the last time you replaced other parts of your drivetrain?

hahahaha awesome.

have you actually measured the chain now?
is it really longer than it was before, or did your wheel just slip in the dropout?

How would he be able to do this? Very unlikely he measured the chain before installing it. Seems like the only way would be to compare it to a brand new chain of the same model.

Worst advice ever.

Not at all.

the same way you'd check a used chain for wear. 12 links = 12"

slack=good

Interesting, I never check chains that way, I've grown accustom to using a precison gauge.
http://www.mtbr.com/reviews/Tools/Rohloff_Caliber_2.jpg

where does this come from? Seriously?

is there no engineer or anyone that has taken an introductory physics class to back me up on this?

yeah, i leave enough slack so that my chain drags on the ground.

Too much slack isn't what's being suggested, but I've noticed a trend were people think they need their chains as tight as possible and all this does is create friction and wear out the drivetrain really fast.

I'm an engineer and a physicist.
by slack i mean 1/2-1/4" of vertical play.

tight chains like seely described (i.e. no vertical free play) are a recipe for destroyed bearings and worn chains and cogs