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mad11:11one
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Discussion Starter · #1 · (Edited)
Frame stiffness VS. weight/material has really caught my interest lately.....
:)
i have a question....
How much stiffness is lost in a frame as it's size increases?

The tetrahedron shapped rear brace (rear triangle) has been shown in experiments to flex in "one piece" and add to what we percieve as bb flex, wheel flex, etc... ( regardless of chain-seat stay length/ material..)

but
if i jumped on a 50 cm Prince and than jumped on a 60 cm identical setup.... how different would (or could ) it feel?
Do carbon engineers compensate in thickness to make up for the added flex in increased seat/down/top tube length?

I guess my question is, would a bike model feel the same to David Etxebarria as it would to Hincapie? If not, wouldn't reviewing a frame be more directly relative to the size and weight of the reviewer than we think?:confused: -- or care to look at when assessing a review...?

(on a side note: i understand the difficulty in testing outcomes of this experiment, as i would never expect a 5'3" rider to jump on a 60cm frame with any comfort, and vice versa)

so who knows?
 

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No; they would not flex proportionately the same. Many frame manufacturers actually state in their literature that they vary tube sizes/shapes/carbon layups so that the frames will "ride the same" regardless of size. There are too many variables to make that possible.

" ...would a bike model feel the same to David Etxebarria as it would to Hincapie? If not, wouldn't reviewing a frame be more directly relative to the size and weight of the reviewer than we think? -- or care to look at when assessing a review...?"

That's the problem with reviews. You have to take them with a salt shaker of salt.
 

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Steaming piles of opinion
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There's a little bit of 'what does it matter' in the question, isn't there? One person can't ride both the 50 and the 60 reasonably, so it hardly matters what the bike that doesn't fit might feel like.

But there's an interesting notion of whether you can trust the review of someone a different size. The answer there is a resounding 'no', but it has nothing to do with size. Experiences simply don't translate well. If nothing else, the larger and smaller riders simply aren't going to be the same sort of riders - climbers v sprinters, spinners v mashers, etc. Given all that, they'd not experience the bikes the same, even if there was some sort of proportionality.

One interesting bit that sometimes goes unthought in this discussion: For any given person, the largest frame they can ride will have the best stiffness to weight (on a design-consistent basis). Cantilevered structures are always less stiff than fully supported ones. If it weren't so, we'd all be riding bikes whose top tube ran below the bottle bosses. The triangle itself might be stiffer, but it's for naught once you get out to the contact points.
 

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mad11:11one
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Discussion Starter · #4 ·
danl1 said:
There's a little bit of 'what does it matter' in the question, isn't there? One person can't ride both the 50 and the 60 reasonably, so it hardly matters what the bike that doesn't fit might feel like.

But there's an interesting notion of whether you can trust the review of someone a different size. The answer there is a resounding 'no', but it has nothing to do with size. Experiences simply don't translate well. If nothing else, the larger and smaller riders simply aren't going to be the same sort of riders - climbers v sprinters, spinners v mashers, etc. Given all that, they'd not experience the bikes the same, even if there was some sort of proportionality.

One interesting bit that sometimes goes unthought in this discussion: For any given person, the largest frame they can ride will have the best stiffness to weight (on a design-consistent basis). Cantilevered structures are always less stiff than fully supported ones. If it weren't so, we'd all be riding bikes whose top tube ran below the bottle bosses. The triangle itself might be stiffer, but it's for naught once you get out to the contact points.
--------------------

danL1.... once again
whoever you are...
thank you.

your avitar is most fitting my friend.
:)
 

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danl1 said:
One interesting bit that sometimes goes unthought in this discussion: For any given person, the largest frame they can ride will have the best stiffness to weight (on a design-consistent basis). Cantilevered structures are always less stiff than fully supported ones. If it weren't so, we'd all be riding bikes whose top tube ran below the bottle bosses. The triangle itself might be stiffer, but it's for naught once you get out to the contact points.
I assume the catilevered structures you are talking about are long seatposts and stems required on small frames.

And if that is the case I agree with you when the rider is seated. I have often been critical of compact frames, because I believe the seatpost dictates more of the ride than the frame.

However, the times when the rider is most critical of stiffness is when he is out of the saddle. At these times the seatpost length is irrelevant. So if the manufacturer uses the same thickness, lay-up schedule, material throughout the size range, than the smaller frame will be stiffer.
 
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