Thanks for "enlightening me..."
Are you attempting to ask/say:
-the issue of crank/bb stiffness is irrelevant because the benefits of increased stiffness in this area are lost in frame flex inefficiencies/noise?
or,
"who cares about a stiffer crank, you don't lose energy there, because the frame is flexing already!"
If this is what you are trying to say,
- frame flex does not really work that way in regards to the drivetrain.
My distinction between BB and "commonly referred to as BB" is actually meaningful in a real discussion of the issues you attempt to raise. The *only* source of flex in the actual BB area is the spindle/crank. This interface is subject to quantifiably different forces than the area you seem to be referring to in your over-generalization. To simplify: flexion of the spider, crank arms in 3 axes relative to the BB centerline, and chainring flexion are all factors in this phase of energy transfer, and are not, or manifest differently in a discussion of frame flex.
- You *are* losing energy there, so yeah, it does matter.
Well, maybe it doesn't matter for you, but it does for many riders. ST BBs are flexy, measureably so, and not in a way that is completely lost in the noise of frame flex, which doesn't affect power transmission in a bicycle in the same way that BB flex does. Why ride something you know to be less efficient, even if microscopically so?
I stopped using Campy cranksets when I actually saw a set of stiffness tests for the Record crank/BB (and no, I don't have them sitting around anymore, sorry, wish I did.) They are markedly less stiff than any of the competition, almost all the difference comes from the BB, and the results were more than enough to convince me.
PS - I still have a set of Record AL cranks, 172.5, sitting in the closet; sold the other two sets. I will make somebody a good deal on them... but will also tell them up-front that a set of the cheap FSA AL cranks, with an ISIS bb will outperform them on any given bike (as long as the crappy bearing set holds out, anyways..)
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