Rotule wrote:
why would you need something stronger than this carbon piece, if that piece is olded by two straps (seriously the weekest link is the straps not the bar
a carbon piece this thick can take a shit load of tension and "flambing" (sorry not sure with my english on this one))
I agree with you that the whole setup still look a little bit prototype, but he's doing an awesome job and i'm sure he'll figure it out soon
Sorry that I started a tangent, but since this particular tangent is a direct consideration of this thread, I'll discuss this carbon fiber thing a bit further. It is an amazing material! Very strong for it's weight. Tensile strength is incredible. But we scientists refer to CF as "strong" but not "tough". In simple terms, it can handle incredible amounts of force when bending or stretching, but not nearly as much when exposed to compression or impact shock.
This concept is widely known and very easily demonstrated. Take a piece of CF (like the referenced spreader bar for example) and try to bend it. As you suggest, it will be crazy strong. You will barely be able to bend it. But.... take out a sharp heavy object and give it a smack. CF cracks rather easily under sharp impact. This is because as soon as the epoxy (which is rather brittle) gets compromised, each fiber must act as an individual directional fiber. When glued into a bundle, the fibers are incredibly strong, but individually, the fibers aren't very strong at all.
This is where the next big problem for a CF spreader bar comes in. Steel is both strong and tough. It can handle high force and high energy. A fairly significant amount of deformation is acceptable and won't compromise the integrity of the bar. And because it can deform, it usually doesn't simply crack and shear off. IOW, a small dent from being tossed against a sharp rock, or taking a nice hard hit from the rail of a TT board, isn't a big deal. Conversely, a single crack in a CF bar (even one that might not be apparent except under very close inspection) can result in catastrophic failure, and failure usually is catastrophic.
This catastrophic failure characteristic of CF is widely acknowledged in other sports like cycling. Some road cyclists use it for its light weight, and try to handle it with kid gloves. OTOH, it is generally considered a poor choice for mountain biking. Any decent crash or gouge and the whole frame is toast.