The thickness is not as important as the quality of the carbon. My Quad 12 has a 2.5mm chassis and it has less flex than my buddies rug rat with a 3mm chassis. If the carbon has any filler in it, it will cause more flex. Just look at the switchblade and reflex chassis. The older chassis had no coloring or filler and is way stiffer than teh new one. However they are both on the heavy side. A chassis that is .110-.120 in thickness without any filer or coloring is more than stiff enough for carpet.