I can second Jans observation of the ride qualities of womens frames of the swan-neck style. I also have seen several broken cheap womens frames. Thay usually break at the lug where the lowered top tube meets the seat tube. It is quite obvious taht they break there, because that's where the most stress occurs. And I am talking about really heavy ga-pipe tubing and not lightweight stuff. To my opinion it is just faulty design. One can discuss if it really makes sense at all, since most women racers prefer normal diamond frames.
Michael Schmid Oberammergau Germany Tel.: +49 8821 798790 Fax.:+49 8821 798791 mail: firstname.lastname@example.org http://www.zunterer.com
-----Ursprüngliche Nachricht----- Von: email@example.com [mailto:firstname.lastname@example.org] Im Auftrag von Jan Heine Gesendet: Sonntag, 28. Dezember 2008 02:45 An: Mark Stonich; email@example.com Betreff: Re: [CR]Lightweight "Woman's" frames. Seat post diameter?
At 6:19 PM -0600 12/27/08, Mark Stonich wrote:
>>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).
>Many, if not most, would call that Barra a mixte. It appears to
>have some interesting ovalizations.
Terminology is ambiguous, but I feel it is important to distinguish
between the Barra frame style (single top tube) and the twin-lateral
"mixtes" made by Peugeot et al. Yes, Barra ovalized many of his
aluminum frames to add lateral stiffness.
>>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.
When you consider that a women's frame moves the top tube half-way down the frame, you already have a lot more vertical compliance, even if you do not bow the seat tube. If you eliminate the top tube altogether (like some city bikes), you'll get even more flex and comfort. How much is enough and how much is too much? Having ridden some older German "swan neck" bikes with what basically are two down tubes and no top tube,
it is disconcerting to have your head angle change by several degrees
as you hit a bump, and to have the front end shimmy as you pedal at
80 rpm and 15 mph _with_ both hands on the handlebars.
>>> 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.
I doubt that any calculation and much testing was done. They probably built a prototype, gave it the wife of the head engineer to ride on a 3-day tour, and then went into production. Even today, when you look at many mixte bikes made by modern makers, few understand the reasons behind various design features. I've seen twin laterals that were parallel all the way to the seat tube and then splayed out (no triangulation of the main triangle!), and another constructeur-style mixte where the extra seatstays join the seatstays rather than attaching at the dropouts. This design simply transmits the bowing of the seat tube to the seat stays, which provide little resistance, instead of the dropouts, which provide a fixed point. (If you want to bow the seat tube, you don't need the extra stays at all.)
I am sure all these bikes work, but that does not mean they are optimized like a traditional men's frame is.
Jan Heine Editor Bicycle Quarterly 140 Lakeside Ave #C Seattle WA 98122 http://www.vintagebicyclepress.com