Easiest option is the clamp you could use a copper pipe or similar to maintain the structural integrity of the carbon tube to avoid over tightening it of the right diameter.
Clamp on front derailleur carbon frame.
Parlee carbon front der braze on adaptor 28 6mm.
There s no need to treat the underlying carbon before installing a clamp on front derailer.
Traditional steel alloy front derailleur clamps look clumsy and weigh a lot more than what they need to.
Our 1 piece carbon construction cuts material to an absolute minimum with a very simple understated design.
The handmade clamps are designed to be as strong as their metal counterparts but safer to lightweight carbon titanium and steel tubes.
Unique 1 bolt carbon design won t dent or scratch frames.
Sizes available are 28 6mm 31 8mm and 34 9mm.
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A torque key and patience are required for that.
Our renowned carbon front derailleur mount is now available for all frame sets not just our own.
All parlee frame sets use 34 9mm clamps.
Our front derailleur clamp have been designed particularly with the weight conscious rider in mind.
The clamp has no moving parts or pivots that can damage lightweight carbon fiber titanium or aluminum seat tubes.
That said as a framebuilder who used to subsist on doing a lot of repairs on steel frames i have dealt with seat tubes that were cracked at the front derailleur braze on.
On carbon frames tube spec generally seem to run big rather than small once you figure in the clearcoat.
Your torque wrench may have been on spec it is possible that the tube is slightly oversized where the derailleur clamps at.