Originally Posted by
Mark Kelly
I couldn't disagree more.
Torsional rigidity of the head tube is a major determinant of the bikes road manners. More is always better. Slitting the tube transforms the torsional stress on the tube into shear stress on the bond line. Bonding epoxies are deliberately rubberised so they can absorb these stresses by deforming, so the bond line will elastically slip.
Net result is a bike that gets squirrely in hard corners.
none of this is obvious to me, seems like speculation with a potentially flawed mental model of the proposed system. Seems to me that you are saying that the carbon tube is needed to take torque, but that the bond line can't stand shear. Seems internally contradictory. It's not like anyone has ever tried having a wimpy head tube before. And I'm not sure that a well bonded slit tube would necessarily have these issues anyway. I think the carbon tube mostly takes stresses from inserting
the headset and possibly takes up some bending stresses which would be adequately addressed by a slit tube.