At 12/27/2008 05:45 PM -0800, Jan Heine wrote:
>>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.
The Italians maybe, but not Schwinn. Despite knowing one of their engineers, I could not get them to build my '77 Paramount tandem with a couple more inches between the riders. Too expensive to test for a one-off.
Worked out for the best though. Jane hated the cramped quarters so
much I had to learn to build frames so I could make a tandem with 5
more inches between us. (27" back when Santanas were considered
roomy at 24.5")
> 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.)
IMHO the best solution is to merge the mixte stays with the seat
stays at the upper dropout tang. No chain clearance issues and you
aren't feeding a load into a part of the dropout that wasn't designed
to resist
one. http://bikesmithdesign.com/
Even better would be custom forged or cast dropouts with 3 tabs or
sockets, having the middle one offset outward to provide chain clearance.
>I am sure all these bikes work, but that does not mean they are
>optimized like a traditional men's frame is.
That may depend on the situation one is optimizing the frame for. Not that I'm convinced the traditional diamond frame is optimum. When I build myself another frame I'll give serious consideration to your (I assume tongue-in-cheek) suggestion to attach the seat stays to the middle of the seat tube. (Wish I still had access to FEA software.)
Mark Stonich;
BikeSmith Design & Fabrication
5349 Elliot Ave S. Minneapolis, Minnesota 55417 USA
Ph. (612) 824-2372 http://bikesmithdesign.com
http://mnhpva.org