Someone at Interbike jokingly asked if maybe the wheel folks (or aero folks) and certain frame designers maybe missed some memos. As the OP pointed out you have these super aero rims just in front of big fat wide square etc etc unaero looking tubes.

I'm not an engineer, nor do I understand the intricacies of carbon fiber, but I hope there's a functional reason for such frames. My guess (and just a guess) is that it has to do with "laterally stiff, vertically compliant" phrase that seems so over used.

Personally I'd be curious to see how a twin downtube bike would work. This would get the width without building an aero wall. Kind of like the bi-titan etc by Colnago, but one that didn't crack after a few weeks. You could envelope part of the front wheel, have aero struts to tie the two sides together, and have a lot of vertical flexibility on an extremely wide frame (figure minimum 68 mm wide, max would be 90-100 mm, based on BB width).

Of course there's the problem of having 2 extra tube sides, more joinery, etc etc. But, hey, nothing's for free.

I have a downtube that's oval vertically at the head tube and oval horizontally at the BB. It's pretty narrow up top (compared to my SystemSix especially). I "feel" more aero riding the bike. And it's plenty stiff for me, and I really hate a frame that is marginally noodly.

cdr