Originally Posted by
FBinNY
Again -- it's not the material per se. It's the application, meaning the overall design, construction, and intended purpose.
It's perfectly possible to build a CF frame for a 300# rider or even heavier. But that's not what the available frames/bikes are built for.
And to further that insight, it's relatively easy for a framebuilder to spec heavier tubes for the large rider. It's possible, just not likely, that someone could come up with new molds, fabric layups, etc. to build a slightly heavier CF frame. Those things are so automated and specifically tooled that it's not financially viable to build a custom CF frame for a heavy rider.