Re: [CR]Lightweight "Woman's" frames. Seat post diameter?

> At 12/26/2008 09:03 PM -0800, Jan Heine wrote:
>>Most of the French constructeurs used Reynolds 531 for their women's
>>bikes. For those not familiar with the design, a photo is here
>>
>>http://www.vintagebicyclepress.com/images/barrafull4.jpg
>>
>>Not immediately obvious, a single top tube goes is supported by an extra
>>set of stays (unlike a "mixte" that has two long stays that run all the
>>way from the dropouts to the head tube).
>
> Jan,
> Many, if not most, would call that Barra a mixte. It appears to have
> some interesting ovalizations.
>
>>>Good steel can flex quite a bit without taking a set. Mixte stays make
>>>the frame stiff in the vertical plane. Which is fine for bridges.
>>>Bicycles, not so much.
>>
>>Is it stiffer than a traditional men's frame?
>
> Probably not. But I believe the traditional diamond frame is too stiff in
> resisting vertical loads.
>
>> I don't see how the extra seat stays transmit extra shock to the seat
>> that isn't already transmitted by the standard, upper seatstays... Of
>> course, eliminating the extra stays on the "constructeur" women's frame
>> would cause the entire frame to flex like a giant spring when you hit a
>> bump, front or rear. So it would create a frame that is much less stiff
>> than a "men's" frame.
>
> That, and light weight with a low step-over height, is what I'm after.
> Since a crash on last year's 3 Speed Tour of Lake Pepin she's found
> mounting her Robin Hood easier than her mixte.
>
> I'm not trying to do something experimental. Paramount, Cinelli, Colnago
> etc. have proved that it can be done. I just want to "reverse engineer"
> by determining the wall thickness they used.
>
>>You could create a similar men's frame by moving the seatstays way down so
>>they attach in the middle of the seat tube, rather than the top. In both
>>cases, the loads of bumps would bow the seat tube in the middle. I wonder
>>whether that is a good idea.
>
> Might be a very good idea. Although there are a couple of practical
> considerations. Brake cable routing might be a problem unless you put the
> brake on the chainstays. Rack mounting too.
>
>>> I'm not surprised that some are reporting 27.2 mm seat posts on the
>>> highest quality frames.
>>
>>Was that a conscious design choice based on calculating stresses, or was
>>it just an issue of using standard tubing?
>
> My guess is that they started with the question "Will a standard tube
> work?" and then did calculation and testing.
>
>> If a standard 8-5 seat tube works even on a women's frame that bends in
>> the middle, doesn't this mean that when the same tube is used on a men's
>> bike, it's totally overbuilt?
>
> Perhaps, since some modern competition bikes are built with no seat tube
> at all. But again there would be practical considerations like clamping
> a derailleur onto too thin a tube and the stresses at the
> TT/ST/SS/pinchbolt joint.
>
>>The women's bikes for the technical trials all used the "constructeur"
>>frame design (single top tube, extra stays). Either Herse, Singer and
>>Routens did not realize they did not need those extra stays (unlikely), or
>>the stays were needed with the superlight tubing these builders used, when
>>ridden hard on very bumpy roads.
>
> I'm sure it was the later. But being French they had a mixte mindset too.
>
>>One issue with many women's bikes is that they aren't ridden hard. (Avid
>>female riders usually prefer "men's" bikes).
>
> And some "avid" riders, such as Jane, don't ride "hard".
>
>> So the fact that they haven't broken does not always mean much. It would
>> be interesting to get some data under controlled conditions.
>
> I wonder if Schwinn did machine testing.
>
> Mark Stonich;
> BikeSmith Design & Fabrication
> 5349 Elliot Ave S. Minneapolis, Minnesota 55417 USA
> Ph. (612) 824-2372 http://bikesmithdesign.com
> http://mnhpva.org