Hello Mark. To your original question, my wife's 531 Raleigh mixte has a 26.4 seat post.
One observation to add for you on your project: the mixte design is not optimized for step-through. Not sure how high a priority this is for you and your wife in this design, but if it's important, I think you are on the right track in your original interest in a ladies frame rather than a mixte. The top tube is quite high on a mixte (compard to ladies frames) and even on the small mixtes I have built(up) for my wife, I find it uncomfortable to kick up a leg high enough to get it over that top tube and would always lift my leg over the rear of the saddle if it were my bike. I watch her get on the bike and she doesn't complain because she loves the bike, but it's not an easy bike to mount. Maybe this is why "ladies bikes" persisted despite long coexistence with the apparently superior mixte design--I think a woman wearing a skirt would have trouble being modest in the usual way while mounting a mixte. Although my wife is sentimentally attached to the double lateral style mixte over the constructeur style with single top tube, the extra width of the double lateterals make it more difficult to mount and dismount, in my experience.
Perhaps the advantage of the mixte, rather than modesty with a skirt, is to allow a hard working Frenchman(or woman) to mount a _little_ more easily on a porteur bike loaded front and rear with building supplies. Saw this in person recently one early morning in Caen where they still ride into the city on mixte bikes with plumbing or glazier or carpentry supplies stacked high front and rear and these guys had no chance to mount except in the middle, while the big loads required a stiff frame too.
Even the few extra inches of clearance that you get with the much lower "top" tube of a ladies bike makes mounting a lot easier. And it also allows that elegant dismount where, while slowing to a stop, one stands on one pedal while passing the other leg through to the other side of the bike, and then steps down onto the ground onto that crossing foot. Just like the clyclo cross dismount I do but without the extravagant scissor kick back over the saddle. If on-off ease is important then I'd get that top tube lower than mixtes' top tubes--maybe making extra seat stays that meet the very low top tube to reinforce the seat tube (as Jan recommends) but without the straight line from drop out to head lug that trad mixtes have. This might look good too, like the double chainstay bikes that Aherne makes, if the low extra seat stays look like extra chainstays. Wouldn't have the rigidity of the mixte design, which may not be necessary, but might still have the seat tube reinforcement to allow a moderately light seat tube.
I saw bikes sort of like this in London a couple years ago that had double lateral mixte-like tubes from head lug to dropouts, but instead of a direct line, they took a deep swoop and passed a few inches above the bb on their way to the dropout. I saw women do the elegant dismount on these in Hyde park. These were very new bikes, don't remember the make but it was a common major player (could have been Trek?). They didn't seem to show any of the wobbly traits of "swan neck bikes" mentioned, but I didn't get to ride one.
I wonder wether a straight gauge, or SP, seat tube would be a small price to pay for stabilizing the low top tube on a trad. ladies low top tube design without extra seat stays.
One other style mixte/ladies bike I saw was a Holdsworth getting off a train a few years ago in Winchester, I think, walked by a fit elderly woman who patiently described the bike to me. Instead of a top tube it had double lat. stays from head lug to seat tube, where they stopped--no third pair of stays. And very delicately brazed at the seat tube--just the point of the scalloped stay touching the side of the seat tube. She said she (Carrdice) toured this bike all over the land.
Maybe mixtes are easier on and off than they are for me, because vintage mixtes were in fashion in Paris on a Fall 2005 visit, where sylishly dressed beautiful young women were everywhere riding on old mixtes. They were in skirts, usually mini, with heels, usually 3-4". I watched a lot ;-), hoping to see the dismount process but these women were booking. No explanation necessary to my wife ("honey, I'm just watching to see if she has to kick her leg up to dismount") because my wife (also beautiful) was just as transfixed by lovely women everywhere on mixtes.
Best wishes on your project, Mitch Harris Little Rock Canyon, Utah, USA
On Sat, Dec 27, 2008 at 5:19 PM, Mark Stonich <mark@bikesmithdesign.com> wrote:
> 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/
>>
>> 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