Originally Posted by FrankBattle
I'd hazard a guess at the "obvious reasons:" Carbon's generally lighter than alloy (by volume, for example). Lighter = Weaker in a lot of people's minds. For something you crank down on literally, an alloy would bend where carbon would snap ..
NOW, how true is this?
Not very in today's world of material science/engineering/technology.
FWIW, Carbon can be "stronger" than alloys; i.e. can withstand more stress before failure. When said failure occurs, though, you will have different signatures .. maybe that's where the fear is ..
Largely, I think it's mental. People are still getting used to the idea of something as light as Carbon being stronger than alloys/metals. In case it's not obvious, most chain rings even on carbon cranks are made with alloys .. it's mostly always the crank arms that are Carbon.
Well, I think you hit the nail on the head, which is why I'm leary of carbon (well, that and the needless expense). I'm not leary of carbon overall, just cetain parts, namely the crankset and handlebars/stem. As you said, chance of failure isn't really any greater than alloy, but when it does fail it's a catastrophe. I read last year of a case here in CO where a guy was riding in a group ride, got out of his saddle to hammer up a hill, and the crankarm snapped, plummeting him down on to his toptube and handlebars, and ending with a nasty crash and a trip to the hospital. If your handlebar suddenly snapped, you'd also experience a complete lack of handling and balance, and down you go.
If I bought a bike that already came w/ a carbon crank or handlebars, I'm not so worried about it that I'd switch them, but when building up my own bikes, I stick w/ good ol' metal...
I've got an FSA Gossamer Compact MegaExo on my road bike and love it; have had no problem. I've got an FSA Energy Compact (ISIS) that I plan on using on my cross bike.
Structural concerns aside, as they probably are overinflated as FrankBattle said, the other thing to ask when debating btwn alloy and carbon cranks, is - is it worth the money? You can find a brand new Gossamer/Energy crankset on eBay pretty cheap usually, anywhere from $90-$170. Once you get up into the carbon models, you're looking at $250-$500+. They're only a tiny bit lighter, and unless you're a Cat1 hammer, you're not likely to notice any difference in stiffness/performance.
My two cents....