is it a scratch in the paint??
was there an incident like a crash, the bike falling over, or something heavy falling on the tube??
it would be unusual for the tube to split like that from just riding unless there was a major defect in the manufacturing of it.
thats the seat tube? I was told by my lbs that there is very little weight supported by that tube due to the diamond shape design of frames. and its just there to mount your front der and a water bottle to.
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2010 Kestrel RT900SL, 800k carbon, chorus/record, speedplay, zonda
2000 litespeed Unicoi Ti, XTR,XT, Campy crank, time atac, carbon forks