Originally Posted by LóFarkas
The steerer is a different story. Everyone agrees that carbon doesn't really like things being clamped onto it. If you overtighten, it can and will crack the carbon. I guess its surface is not as hard as metal anyway, so the edge ot the clamp could damage the carbon if it has burrs, or you crash etc.
Torque wrenches are your friend. Besides, carbon handlebars (which are clamped onto the stem) have been used on mountain bikes for years, where they're exposed to arguably more torque, far more vibration, and greater impacts as well. If it's installed correctly, you probably don't have anything to worry about.