Having read a fair amount of reviews (and presuming those authors have read the marketing bumpfs), it sounds like the modern frame double diamond design is driven more by aerodynamics than comfort:


- Flat top tubes present the smallest forward aspect relative to any sloping top tube design
- Dropped seatstays put the seatstay/seat tube joint right in front of the top of the tire, where the air is already being spoiled anyway, rather than higher up, which adds to its own drag
- Standard for these days D-shaped seat and down tubes

Comfort is thrown in by way of wide tires, flexy seatposts, and odd suspension designs (ahem, Roubaix and Domane). The ‘default’ race design these days (as outlined above) doesn’t really provide for inherent comfort due to the lower amount of exposed post (flat top tube) and tight rear triangle (dropped stays). An argument could be made that the seat tube itself could be made to flex at the seat stay joint, but any flex there would also impact the top tube and head tube joint as the seat tube bends and effectively shortens that side of the triangle.

So short version… first conclusion: dropped seat stays and flat top tubes are for aero, not comfort.

Of course, regardless of whether your stays are high up or low down, this all happens behind a rider’s thighs and feet, which cause plenty of airflow disruption of their own anyway. Manufacturers are trying to tell us that an extra three inches of half-inch wide seat stay will provide meaningfully more drag, even though it’s primarily in the wash of my 7” diameter thighs and size 10 shoes as they go round and round? Sure, when the absolute most marginal race gains are to be considered, the tiniest fraction of a watt and handful of grams that a shorter stay provides could prove beneficial - or at least, matching what the big boys do is good for optics, both at the start line and on the showroom floor. After all, when Specialized shows up with its new Tarmac, Bianchi and BMC can’t be seen putting "last year’s” technology out there.

Short version, conclusion 2: Marketing wants to make sure our new bike doesn’t look old next to the other guy’s new bike