Broken derailleur under warranty?

[Llan Giant]

I bought a Giant Defy SL1 road bike 6 weeks ago. No problems with 190 miles of pleasure then for no reason, on a slight incline, 12mph, a snap was heard and the bike came to an abrupt stop, throwing me into the road! Once I got up, I saw the Di2 derailleur was jammed in between the wheel and the frame. The derailleur, wheel and frame are damaged. The frame has a large gouge in it and the wheel has broken 4 spokes. There was no reason for the failure, slow speed, under very little pressure and was not changing gear at time. One of the component must have been faulty. Can anyone advise where I stand with the warranty on the £4500 bike? I look after my bikes and there wasn't a mark on it until this happened. Please help!!!

 

[RecordAceFromNew]

The most likely scenario is a spoke catching the rear mech. The moment that happens, the spoke will pull the mech backwards and you get all the phenomena you described. That is one of the reasons why some people have large pie plates, but they are most unfashionable...

There are many possible causes but the most likely is badly adjusted L limit screw on the rear mech (see 2/3rd way down here), allowing the mech too much leeway inboard and to catch a spoke when it is onto the large sprocket.

Another possible cause is hub/wheel fault, e.g. under preload for sealed bearings, allowing the hub to drift and therefore a spoke onto the mech.

Of course bent mech, bent spoke etc. could theoretically do the same.

If you haven't been messing with the bike and it was never dropped e.g., then it is a warranty claim in my view.

 

[Llan Giant]

The most likely scenario is a spoke catching the rear mech. The moment that happens, the spoke will pull the mech backwards and you get all the phenomena you described. That is one of the reasons why some people have large pie plates, but they are most unfashionable...

There are many possible causes but the most likely is badly adjusted L limit screw on the rear mech (see 2/3rd way down here), allowing the mech too much leeway inboard and to catch a spoke when it is onto the large sprocket.

Another possible cause is hub/wheel fault, e.g. under preload for sealed bearings, allowing the hub to drift and therefore a spoke onto the mech.

Of course bent mech, bent spoke etc. could theoretically do the same.

If you haven't been messing with the bike and it was never dropped e.g., then it is a warranty claim in my view.

Thank you so much for the in-depth response. The bike has not been dropped or damaged in any way, I even polish it after a journey (sad I know!) Have to contact the bike shop today and see what they say. I hope they sought it out quickly as I have a London to Paris bike ride for charity in three weeks time. Will have to train on the exercise bike in the meantime. Thanks once again.