Teach an old guy about "new frame sizing"



Michael Press wrote:
> In article
> <[email protected]>,
> "Ozark Bicycle" <[email protected]>
> wrote:
>
> > IRRC, when compact frames were first introduced, proponents argued that
> > the extended seatpost made things stiffer, as the seatpost was stiffer
> > than the seat tube. That seemed to be questionable, but this new
> > arguement.....well, what can I say?

>
> Fascinating argument. A strut clamped at one end is
> stiffer than a strut pinned at both ends.
>
> --
> Michael Press


I think this is something of a distortion, as Ozark does not
acknowledge what was supposedly 'made stiffer'. As I understood the
argument (and I do not give it any particular credence), the compact
frame allowed for stiffer diamond structure (both front and rear
triangles), and as such a stiffer bottom bracket, as the tube spans
were shorter. Because cyclists (or more accurately, those who market
to cyclists) view BB stiffness as paramount for proper power
transfer/efficiency, any potential losses due to seatpost flex were
conveniently ignored (I have no clue as to whether flex from the
unsupported strut actually results in any such losses of efficiency).

SYJ
 
SYJ wrote:
> Michael Press wrote:
> > In article
> > <[email protected]>,
> > "Ozark Bicycle" <[email protected]>
> > wrote:
> >
> > > IRRC, when compact frames were first introduced, proponents argued that
> > > the extended seatpost made things stiffer, as the seatpost was stiffer
> > > than the seat tube. That seemed to be questionable, but this new
> > > arguement.....well, what can I say?

> >
> > Fascinating argument. A strut clamped at one end is
> > stiffer than a strut pinned at both ends.
> >
> > --
> > Michael Press

>
> I think this is something of a distortion, as Ozark does not
> acknowledge what was supposedly 'made stiffer'.



Well, let's be clear then: the arguement was that the shorter seat
tube/longer seat post combination offered by a compact geometry frame
was "stiffer" in that part of the frame (i.e., seat tube/seat post
taken together) than the more traditional, longer seat tube with a
shorter seat post design. Now, the arguement has shifted 180 degrees.

Clear enough?



> As I understood the
> argument (and I do not give it any particular credence), the compact
> frame allowed for stiffer diamond structure (both front and rear
> triangles), and as such a stiffer bottom bracket, as the tube spans
> were shorter. Because cyclists (or more accurately, those who market
> to cyclists) view BB stiffness as paramount for proper power
> transfer/efficiency, any potential losses due to seatpost flex were
> conveniently ignored (I have no clue as to whether flex from the
> unsupported strut actually results in any such losses of efficiency).
>
>


That was/is a different marketing tack. And equally specious.

But, after all, it's just marketing BS, eh?
 
In article
<[email protected]>,
"Ozark Bicycle" <[email protected]>
wrote:

> SYJ wrote:
> > Michael Press wrote:
> > > In article
> > > <[email protected]>,
> > > "Ozark Bicycle" <[email protected]>
> > > wrote:
> > >
> > > > IRRC, when compact frames were first introduced, proponents argued that
> > > > the extended seatpost made things stiffer, as the seatpost was stiffer
> > > > than the seat tube. That seemed to be questionable, but this new
> > > > arguement.....well, what can I say?
> > >
> > > Fascinating argument. A strut clamped at one end is
> > > stiffer than a strut pinned at both ends.
> > >
> > > --
> > > Michael Press

> >
> > I think this is something of a distortion, as Ozark does not
> > acknowledge what was supposedly 'made stiffer'.

>
>
> Well, let's be clear then: the arguement was that the shorter seat
> tube/longer seat post combination offered by a compact geometry frame
> was "stiffer" in that part of the frame (i.e., seat tube/seat post
> taken together) than the more traditional, longer seat tube with a
> shorter seat post design. Now, the arguement has shifted 180 degrees.
>
> Clear enough?


Affirmative.

> > As I understood the
> > argument (and I do not give it any particular credence), the compact
> > frame allowed for stiffer diamond structure (both front and rear
> > triangles), and as such a stiffer bottom bracket, as the tube spans
> > were shorter. Because cyclists (or more accurately, those who market
> > to cyclists) view BB stiffness as paramount for proper power
> > transfer/efficiency, any potential losses due to seatpost flex were
> > conveniently ignored (I have no clue as to whether flex from the
> > unsupported strut actually results in any such losses of efficiency).
> >
> >

>
> That was/is a different marketing tack. And equally specious.
>
> But, after all, it's just marketing BS, eh?


Gwarsh! I hope not.

--
Michael Press
 
On Fri, 31 Mar 2006 01:37:28 GMT, Michael Press <[email protected]> wrote:

>> Well, let's be clear then: the arguement was that the shorter seat
>> tube/longer seat post combination offered by a compact geometry frame
>> was "stiffer" in that part of the frame (i.e., seat tube/seat post
>> taken together) than the more traditional, longer seat tube with a
>> shorter seat post design. Now, the arguement has shifted 180 degrees.
>>
>> Clear enough?

>
>Affirmative.


Pardon me for jumping back in but hey, it was my thread :) If I
understand correctly, the suggestion is that a shorter seat tube
results in less flex at the BB not at the other end ?

This might actually make sense (from my seat-of-the-pants engineering,
no pun intended), whereas at the top it would seem to be the opposite
effect - i.e. when using a longer seatpost to compensate for a
shorter frame with the seat extension and getting further from the
point where the stays and top tube maximize the rigidity.
 

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