Join Date: Feb 2014
Location: Wind Tunnels of Cheyenne
Bikes: Burley Duet [of some unknown year] (the guinea pig); 2001 Ventana ECDM (the project); And always one less than I think I really need.
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Tandem headtube attachment design question
I can't attach a photo, and I am blind so I had someone describe the following, so I hope it makes sense and someone can make sense of my question.
I'm looking at a custom tandem frame, and the builders have sent along some pics of their completed works, and for the same frame model there appears to be two different designs for how the toptube, lateral [stiffener] and downtube attach to the head tube. Hoping someone has that simple "this is the difference" answer.
In the first design (which I've come across all the time), the toptube attaches to the top of the headtube and the downtube to the bottom, with the lateral somewhere in the middle (usually with all three tubes more or less "touching").
In the design I've never seen before, the downtube is still attached at the bottom of the headtube, but the lateral [stiffener] is attached tp the top of the headtube, with the toptube sloping downward and attaching to the lateral approximately 6" before the headtube joint.
The question is "WHY?"
Some opinions are in regards to standover height (usually more is required for tandems than comparibly sized singles), but both designes are pictured in both larger and smaller frames...If it were standover then why not (in the case of the larger frames especially) just make the captain's part of the frame smaller, or lower where the toptubes meet the seattubes down?
Another opinion is front end stiffness, and it seems the second design would be more stiff on a vertical axis with the lateral/downtube/headtube triangle being "larger," but would this also reduce rotational stiffness around the horizontal axis?
Any opinions would be appreciated. Sorry, no pics...I haven't learned the bikeforums secret handshake yet.