Bang! Chain in spokes!!

[Tel]

Stacked my fixie last night when the chain came off and went into the spokes locking the back wheel. Unfortunately I was out the saddle at the time so all my weight was over the front wheel which resulted in a very interesting shaped wheel indeed! (photo to follow).

It appears that the front wheel is the only part damaged, well apart from my elbow and leg

My question of course is why did my chain end up in the spokes? I presume it is due to my chain alignment?

 

[dan_bo]

chain slack? sounds like a bad 'un that!

 

[rustychisel]

not necessarily but possibly. When you're out of the saddle honking you'd be surprised how much the BB can move laterally, allowing the chain to unship off the chainring, or less often, off the rear cog. This is unusual but combined with a good bump in the road at the wrong time is enough to jump a chain off the cog if it's marginally loose. Even then, the odds are even that it'll go one way or the other. Dunno if a photo will tell you much

 

[Joe24]

Ive had the chain on my old fixed come off before. It came off front and back so nothing locked up.
It could be due to chainline, slack chain or BB moving.
With mine coming off, i got told by the LBS it was the frame flexing(its a huge frame) but people on here didnt think so.
It had come off twice on the same ride, was tight enough and it just came off on on a little bump one time.
The chain did do a very bad, slack-tight-slack so i put it down to that.
I dont think just the frame flexing with throw the chain off, on my cheapo fixed the frame flexes alot and i put alot of power into it and the chain doesnt come off.
But i suppose that if the chain is slack and the frame is flexing abit and you hit a bump it could throw the chain off.

 

[Tel]

Thanks for the input guys.

I think I might invest in some chain tugs...Also what is the best method for checking the chainline? It looks spot on by eye but there must be a way to check.

 

[Joe24]

Thanks for the input guys.

I think I might invest in some chain tugs...Also what is the best method for checking the chainline? It looks spot on by eye but there must be a way to check.

Stand infront of the bike and look down the chain from the top, using the top tube as a straight edge to compare it to. Thats how i have always checked the chain line, and been told to check it.

 

[brodie]

I think it's almost certainly because the chain is too loose; either the hub hasn't been positioned properly in the dropout so the chain is too loose, or the chainring and sprocket are not round so you get loose spots no matter how tightly you adjust the chain.

I doubt it's frame flex, the bottom bracket moving sideways is not going to really affect the ring to sprocket distance.

 

[Joe24]

I think it's almost certainly because the chain is too loose; either the hub hasn't been positioned properly in the dropout so the chain is too loose, or the chainring and sprocket are not round so you get loose spots no matter how tightly you adjust the chain.

I doubt it's frame flex, the bottom bracket moving sideways is not going to really affect the ring to sprocket distance.

No but it does effect chainline.
You might find its the chainring, or in my case, the axle on my rear hub is slightly bent so it makes a slack spot.

 

[brodie]

For the chainring to centre line measurement: measure the ring to seat tube distance then add half the seat tube diameter.

Sprocket to centre line distance: subtract sprocket to dropout distance from half of hub OLN.

 

[Tel]

Thanks for the measurements brodie I'll check them. I done some work on my bike earlier, drilled out the dropouts to ensure the wheel could sit further back (old raleigh 501 frame, see other posts).

Added a couple of links to the chain which I inspected for damage; I found a link which looked slightly damaged so replaced them with the spare I had but on further inspection I found that the chain had a link that had all but completely come away, one side of the link had pulled through. I done some experimenting with my chain breaker and found that it didn't always offer the support required to push the pins all the way through. I've sumised that the pin had not been securely pushed in when I fitted the new chain but was good enough to hold for a while, When I got out of the saddle it stressed the weak link which pulled out and derailed the chain from the chainwheel which made my body fall forward. In retrospect I recall a feeling of "letting go" rather than locking up the back wheel. I think that this is very likely what happened.

But still checking the bike is set up probably is now high on my priority list just as it always should have been. I now have a new chain breaker tool

 

[Joe24]

Thanks for the measurements brodie I'll check them. I done some work on my bike earlier, drilled out the dropouts to ensure the wheel could sit further back (old raleigh 501 frame, see other posts).

Added a couple of links to the chain which I inspected for damage; I found a link which looked slightly damaged so replaced them with the spare I had but on further inspection I found that the chain had a link that had all but completely come away, one side of the link had pulled through. I done some experimenting with my chain breaker and found that it didn't always offer the support required to push the pins all the way through. I've sumised that the pin had not been securely pushed in when I fitted the new chain but was good enough to hold for a while, When I got out of the saddle it stressed the weak link which pulled out and derailed the chain from the chainwheel which made my body fall forward. In retrospect I recall a feeling of "letting go" rather than locking up the back wheel. I think that this is very likely what happened.

But still checking the bike is set up probably is now high on my priority list just as it always should have been. I now have a new chain breaker tool

Dont you have a quick link on there to join the chain instead? This is what i always use instead of just joining them.

 

[MrGrumpy]

any unshipping of chains has been purely down to slack chain and nothing else, yes the chainline on my bike is not straight, was pointed out by LBS, who wanted me to invest in new wheels etc and more or less told me my bike just was not suitable So what i`ve done is bought chain tugs, the wheel no longer slips forward, chain tension is spot on, hasn`t come of yet.

 

[Tel]

Dont you have a quick link on there to join the chain instead? This is what i always use instead of just joining them.

I'm so outta touch. What are quick links?

Ok heres a few pictures.

Bent wheel as a result of crash. Spirit level against sprocket/ chainwheel to try to give a visual edge for chain alignment. Other pics of chain alignment.

 

[Joe24]

I'm so outta touch. What are quick links?

Ok heres a few pictures.

Bent wheel as a result of crash. Spirit level against sprocket/ chainwheel to try to give a visual edge for chain alignment. Other pics of chain alignment.

Can you take a picture of it from the front looking down on the chain? If you get what i mean.
And try and get the top tube and chain not far from each other.
It probably was a slack chain more then anything that caused it.

 

[Joe24]

Ive looked at that picture and i reckon the chainline is out
I spent a while looking at it, then drew a straight line down from the sprocket and the chainring wasnt perfect. That could just be the angle of the picture doing that though.