Originally Posted by
canklecat
I was mostly interested in the theory that, beside an aero position on the bike, an aero kit -- jersey, helmet, etc. -- may be a bigger factor than the bike shape when we're actually mounted on the machine.
Yeah. Clothing and helmets make a pretty big difference. From the data in that video, the old Merckx bike costs about .025 m^2 in drag area compared to the Pinarello, but the retro clothing costs about .07 m^2. We talked about the big effect of clothing in the Cyclingtips Nerd Alert podcast
here.
[Edited to add:] Ballpark, a rough rule of thumb is that a difference of .01 in drag area is worth around 1 sec/km at racing speed, so a difference of .025 is roughly 2.5 secs/km, retro clothing is costs about 7 secs/km, and a round tube bike with retro clothing costs about 10 sec/km compared to tight clothing on a modern bike. If you're not racing, the differences are a bit larger than that, not smaller.