Originally Posted by
dedhed
I thought it answered the actually question in the post title reasonably early in the speil.
"The modulus of carbon fiber is typically 33 msi (228 GPa) and its ultimate tensile strength is typically 500 ksi (3.5 Gpa). High stiffness and strength carbon fiber materials are also available through specialized heat treatment processes with much higher values."
It does, but only gives a partial and misleading picture of reality.
Tensile strength and modulus are only two important factors for a bike frame material. Both are very important, but others - ductility, elongation, "toughness" (defined by Nichols as "the ability to absorb energy by deforming plastically before fracturing"), compression strength, and the material's fatigue limit - are also very important when it comes to a bike's frame. The article you quoted doesn't address them. That's probably because
except for fatigue limit (not sure about carbon in that area), carbon doesn't exactly shine in those areas. Those limitations also have to be considered and addressed.
Here's an example: as Nichols points out, monocrystalline silicon (the substrate used for many electronic components, like microprocessors) is vastly superior to aluminum in a number of areas. If you only focused on those good properties, you'd think it's a great choice for a bike frame.
Unfortunately, it's also brittle as hell (low elongation and not "tough" as Nichols defines the term). So it's pretty much useless for building frames.
Bottom line: you can make many things look "perfect" if you focus exclusively on the things they do well while not mentioning the areas in which they don't. But proper design demands that
all essential factors be considered and any shortcomings addressed - otherwise you're deluding yourself.
Carbon is a good frame material, with limitations that must be addressed. The same is true of steel, aluminum, and titanium. Great frames and absolute dogs can be made from all four - and with "mix & match" combinations (carbon forks on new titanium frames seem to be effectively standard equipment these days).
And what's "great" and what's a "dog" depends on the intended use. A Tour de France racing frame will have very different design criteria than does one intended for consumer use over multiple decades - or it should, in any case. The TdF frame only has to last a month, maybe 3 or 4 if it's used for training prior; a consumer frame should last considerably longer than that.
Or, in other words: perfect solutions and materials don't exist; there are always trade-offs. (smile)