Wednesday, September 19, 2007

Nerdy Carbon-Fiber Physics Discussion

Carbon fiber bike components and frames are nice for the smoother ride and lighter weight they provide. I don't think anybody disputes that. And everybody who switches to carbon is convinced of its value. But honestly, I'm still not convinced carbon, or any other stiff frame or component, makes us faster or more efficient.

It may be true, and I want to believe it, but the skeptic in me isn't completely convinced yet. Sure, those bike engineers have lots of fancy equipment and programs that analyze the forces involved, allowing them to use the least material for the greatest stiffness with maximum comfort. No doubt carbon fiber is not only lighter, for faster climbing, but more comfortable. But does it result in a higher pedaling efficiency?

If you think of a frame, say, as a spring, then applying a certain force to it during a hard sprint will deflect the frame by some amount. A stiffer frame will deflect some smaller amount under the same force. But that smaller deflection doesn't necessarily mean any more force gets to the rear wheel.

Think of a stiff spring; a force applied to a stiffer spring merely compresses it less than that same force applied to a softer spring, but the force applied is the same. And that force doesn't disappear anyway; that energy comes back later (like when you release the pressure on a spring and the stored energy is released back). On a bike that energy might be returned later in the pedal stroke. Less deflection is nice only because it prevents the frame twist from shifting gears by accident and causing brake pads to rub, the better feel it provides, etc. Discuss. ;-)

I can most likely stop wondering; everybody I know who rides carbon is sold on it, and the experts seem to have lots of supporting evidence. But a lot of those experts are selling expensive bikes. Who has seen any real test data proving that energy is lost to a flexy frame or component? By "lost" I mean lost forever (through heat I'd guess), not lost briefly then returned later in the pedal stroke. The easiest way to lay my doubts to rest would be by proving that flexy components actually heat up more than stiff ones when force is applied.

I'm buying a carbon-fiber bike regardless, but....

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