Originally Posted by Raiyn

[color=blue]Coaster brakes have have an arm that is attached to a band that wraps around the chainstay. A Carbon Fiber bike isn't designed to have anything exerting a load on the chainstay other than those found in normal riding. The band would cause a crack possibly resulting in a catastrophic frame failure. It's the same reason why you wouldn't install a kickstand on a CF bike.