At 12/26/2008 10:30 AM -0800, Jan Heine wrote:
>If you want to build a lightweight mixte that offers good
>performance, you'll have to go with a fully triangulated frame such
>as that used by the French constructeurs. On those, an extra set of
>stays feeds the loads from the "top" tube into the rear dropouts.
That's just what I want to avoid. With cheap steel in the seat tube, to avoid failure due to bending loads you have to make it heavy or add mixte stays. 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.
Adding 0.1mm in the seat tube and 0.2mm in the chainstays should give a "woman's" frame similar torsional and lateral stiffness to a mixte. But with better vertical compliance and less weight.
Even if it's a little less stiff against pedalling forces, she's not
a strong rider, never stands on the pedals, and spins her 148mm
cranks quite smoothly. And, I'm a firm believer in what you call "Planing".
>As you suspect, the mixte that feeds loads into the unsupported
>middle of the seat tube requires a beefy seat tube to resist the bending loads.
That is not at all what I suspected. I'm not surprised that some are
reporting 27.2 mm seat posts on the highest quality frames.
>Check out Peter Weigle's article in the "Builders Speak" series of
>Bicycle Quarterly,
I've read it. Just don't agree with much of it. Don't get me wrong, I love the look of mixtes, especially Peter's and Brian Baylis'. But this bike is to be about light weight and efficiency, not beauty and ultimate load capacity.
Mark Stonich;
BikeSmith Design & Fabrication
5349 Elliot Ave S. Minneapolis, Minnesota 55417 USA
Ph. (612) 824-2372 http://bikesmithdesign.com
http://mnhpva.org