Chain length and carbon bike

[Willy]

A friend of mine told me a story that I would like to see if it makes sense. He took his trek carbon Madone into a lbs that works mainly on low end bikes and dirt bikes to have a tuneup done. In the process they replaced the chain. When he rode the bike home the frame broke. He has been told by another shop that the chain was too short and that was the cause of the frame braking. I have not seen the frame. Has anyone heard a story like this?

[kramnnim]

Short chain could result in the rear derailleur get bent and dragged into the spokes and smashed into the chainstay. Friend had that happen when a small rock got jammed in the chain and tangled in the RD.

[dddd]

Almost all modern derailers will freely move completely out of the way of a full-tight chain, as the pivot springs have plenty of travel to allow this while the derailer stays free of the spokes.
So in most cases the minimum safe chain length (two links plus the length when on the largest sprockets) can be checked without even running the chain through the rear derailer.

But a too-short chain can cause failure of the chain, freehub, frame, bb, crankset or cassette.

This is a common mistake when working with full-suspension bikes, each of which has a specific "chain growth" dimension that occurs through the full travel of the rear suspension.
I once broke a chain and ProFlex swingarm after a shop in L.A. replaced my chain without enough length to accommodate the suspension movement.

I recently built a Santa Cruz 5010 and first determined the chain growth by releasing the air from the shock and checking the needed chain length at full extension and full compression. The chain growth figure was exactly two links on that particular bike.

[bewheels]

What part of the frame broke?
Saying that the frame broke can mean a lot of things
- the derailuer hanger broke? ...Generally not considered a broken frame...
- the chain stay (the actual carbon) broke?
- the carbon around the bottom bracket?
- the headtube?
- etc

[oldpotatoe]

A friend of mine told me a story that I would like to see if it makes sense. He took his trek carbon Madone into a lbs that works mainly on low end bikes and dirt bikes to have a tuneup done. In the process they replaced the chain. When he rode the bike home the frame broke. He has been told by another shop that the chain was too short and that was the cause of the frame braking. I have not seen the frame. Has anyone heard a story like this?

Need more info...a way, WAY too short chain could rip the rear der off, killing the RH chainstay, I guess. BUT even a really bungling shop would have to goon it up pretty bad for this to happen. Road bike too, no 'full-squish', MTB issues.

[Willy]

Agree that there is not enough info - sorry for posting too soon. I will try to understand what the details are and then get back to the group.