B/B Stiffness: Comparing apples and Oranges



Brothrmark

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Aug 6, 2005
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Last week I had an opportunity to ride a Specialized Tarmac for a couple days. I was amazed at how much of my pedaling energy seemed to transfer to the rear wheel.
My question is: if I were to swap the crankset on my Allez from the 105 w/ a square taper B/B to a Hollowtech or other external bearing would I feel the same difference, or is it more related to difference in frame stiffness between the two bikes, OR is it because my bike has 170mm cranks and the Tarmac had 172's? [chainring size on both was the same]

Thanks
[Brother]Mark
 

free_rideman

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Mar 20, 2006
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It is probably all three of those. Even the cranks, since putting an extra 5mm of distance in the diameter of the pedaling circle, will increase your torque.

But the frame could be the most responsible for the power, of the three.
 

John M

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Jun 21, 2005
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Brothrmark said:
Last week I had an opportunity to ride a Specialized Tarmac for a couple days. I was amazed at how much of my pedaling energy seemed to transfer to the rear wheel.
My question is: if I were to swap the crankset on my Allez from the 105 w/ a square taper B/B to a Hollowtech or other external bearing would I feel the same difference, or is it more related to difference in frame stiffness between the two bikes, OR is it because my bike has 170mm cranks and the Tarmac had 172's? [chainring size on both was the same]

Thanks
[Brother]Mark
Did the Tarmac also have a lighter, stiffer pair of wheels? If so, I would suggest that the wheels and frame would be the main factors. If the wheels were similar, the frame would probably be the main contributor.
The slightly longer cranks may also give the feeling of some added power.