rear dropout

Miles said:

Hi,

I was out with a friend at the weekend. Their bike was new (large giant
TCR) and they'd done about 500 not-very-hilly miles on it. Going up a
smallish hill, the chain had somehow got stuck and ripped the rear
dropout off and the chain tensioner was bent. When we looked at it,
there wasn't anything caught in the chain, and we were able to get it
going in single-gear mode to get back home.

What would cause this given that they hadn't ridden it far? Should they
be able to get it replaced under warranty? I couldn't see any obvious
cause of this breakage other than some defect in the componentry.

Thanks,

Miles

Can really only be a setup error or defect. Did the derailer get
caught in the wheel at all?

Is the frame destroyed or just the replaceable hanger and derailer?

Nate Knutson said:

Miles said:

Hi,

I was out with a friend at the weekend. Their bike was new (large giant
TCR) and they'd done about 500 not-very-hilly miles on it. Going up a
smallish hill, the chain had somehow got stuck and ripped the rear
dropout off and the chain tensioner was bent. When we looked at it,
there wasn't anything caught in the chain, and we were able to get it
going in single-gear mode to get back home.

What would cause this given that they hadn't ridden it far? Should they
be able to get it replaced under warranty? I couldn't see any obvious
cause of this breakage other than some defect in the componentry.

Thanks,

Miles

Can really only be a setup error or defect. Did the derailer get
caught in the wheel at all?

Is the frame destroyed or just the replaceable hanger and derailer?

No (thank goodness!) - the frame isn't destroyed, just the replaceable
hanger snapped and chain mechanism bent.

It seemed to miss the wheel (all spokes intact) so I don't think it got
caught on the spokes. If it had, I guess the spokes would go first and
not the hanger.

Miles

Miles said:

Nate Knutson said:

Miles said:

Hi,

Quoted message said:

Quoted message said:

I was out with a friend at the weekend. Their bike was new (large giant
TCR) and they'd done about 500 not-very-hilly miles on it. Going up a
smallish hill, the chain had somehow got stuck and ripped the rear
dropout off and the chain tensioner was bent. When we looked at it,
there wasn't anything caught in the chain, and we were able to get it
going in single-gear mode to get back home.

Quoted message said:

Quoted message said:

What would cause this given that they hadn't ridden it far? Should they
be able to get it replaced under warranty? I couldn't see any obvious
cause of this breakage other than some defect in the componentry.

Quoted message said:

Quoted message said:

Thanks,

Quoted message said:

Quoted message said:

Miles

Quoted message said:

Can really only be a setup error or defect. Did the derailer get
caught in the wheel at all?

Quoted message said:

Is the frame destroyed or just the replaceable hanger and derailer?

No (thank goodness!) - the frame isn't destroyed, just the replaceable
hanger snapped and chain mechanism bent.

It seemed to miss the wheel (all spokes intact) so I don't think it got
caught on the spokes. If it had, I guess the spokes would go first and
not the hanger.

Miles

The most common cause of this, by what seems like a pretty wide
margin, is the derailer getting caught in the spokes while the wheel
is moving, which can pull the derailer around with the rotation of the
wheel. This can happen due to either a misadjusted low limit screw or
bent hanger. If it happened the right way, I could see it not leaving
much or any evidence on the spokes, but it's unlikely.

The other mechanical thing that can happen is the chain derails from
one of the derailer pulleys and gets caught between pulley and
derailer cage. Then if the rider keeps pedalling, the derailer willl
get pulled in the direction of up and around the cogset. The causes of
this are somewhat mysterious to me. I've seen it happen due to a
pulley bolt being loose. That would be very weird on a new bike, but
anything is possible. I believe poor shifting technique can also cause
it. And excessively worn pulleys, but that doesn't apply here.

This can also happen if something gets caught in the derailer in just
the right way. It would be weird if whatever that thing was then fell
out and left no trace, but again anything is possible.

Quoted message said:

The other mechanical thing that can happen is the chain derails from
one of the derailer pulleys and gets caught between pulley and
derailer cage. Then if the rider keeps pedalling, the derailer willl
get pulled in the direction of up and around the cogset. The causes of
this are somewhat mysterious to me.

I believe poor shifting technique can also cause
it.

Could being in the small rings front and back create a loose chain
tension and a crooked chain line that could throw the chain within the
derailer if the bike hits a bump in the road?

You were going up a 'smallish hill' when this happened. Had you two
just descended a hill? This would put your friend in a high gear
approaching the hill and he may have down shifted only in front.

Miles said:

Nate Knutson said:

Miles said:

Hi,

Quoted message said:

Quoted message said:

I was out with a friend at the weekend. Their bike was new (large giant
TCR) and they'd done about 500 not-very-hilly miles on it. Going up a
smallish hill, the chain had somehow got stuck and ripped the rear
dropout off and the chain tensioner was bent. When we looked at it,
there wasn't anything caught in the chain, and we were able to get it
going in single-gear mode to get back home.

Quoted message said:

Quoted message said:

What would cause this given that they hadn't ridden it far? Should they
be able to get it replaced under warranty? I couldn't see any obvious
cause of this breakage other than some defect in the componentry.

Quoted message said:

Quoted message said:

Thanks,

Quoted message said:

Quoted message said:

Miles

Quoted message said:

Can really only be a setup error or defect. Did the derailer get
caught in the wheel at all?

Quoted message said:

Is the frame destroyed or just the replaceable hanger and derailer?

No (thank goodness!) - the frame isn't destroyed, just the replaceable
hanger snapped and chain mechanism bent.

It seemed to miss the wheel (all spokes intact) so I don't think it got
caught on the spokes. If it had, I guess the spokes would go first and
not the hanger.

Miles

Not so. Anyone who has had a derailluer-meets-spokes experience will
testify to its ability to damage hanger, derailleur and dropouts
without causing obvious damage to the spokes. On a bike with
horizontal dropouts and fixed (non-replaceable) hanger I have had the
hanger bent at 90 degrees, the dropouts spread to more than an inch at
the ends and the derailleur just about destroyed.

My bet is that you have experienced a similar hanger-meets-spokes
event, most likely caused by setup error in conjunction with unusual
conditions e.g. changing down under load to initiate the event.

Andrew Webster