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