On Bicycles, and.... what else is there?

I did a quick calculation of the effect of the head position on closing a gap. Suppose I'm chasing a group riding @ 40 kph and I can ride with the head up at 45 kph. I can't sustain that pace for too long, so the clock's ticking. I have to close that gap as quickly as possible. I'll do an first-order analysis, which means I assume a starting condition then apply a first-order correction for the small change. In this case the head position change is a small fraction of total wind drag, so the linear analysis should do fairly well. It wouldn't do well, for example, were I to swap my bike for a recumbent... an interesting thought. Furthermore, I neglect drivetrain losses. Calculated powers are "PowerTap" equivalent. I assume drivetrain losses are proportional to transmitted power. Baseline condition: CdA = 0.32 m² M = 65 kg ρ = 1.1 kg/m³ (air density) g = 9.81 m/s² Crr = 0.5% (rolling resistance coefficient) Then I get 40 watts dissipated in rolling ...

I got on the trainer and tried the following two positons, both representing a "chase to close a gap" mode (I couldn't necessarily hold these positions for a half hour, for example). In the top photo, I've got my head up to focus on where I'm going. I used to ride this way all the time. In the bottom, I'm shrugging my shoulders and relaxing my head, looking up to look forward. I can see fine, it's just I'm looking up instead of straight. In the top photo it actually seems my arms are more bent (sloppy of me). Yet despite this advantage, you can clearly see my head is higher above my back: the difference to the bottom position is a full 5.6 cm. With a head width of 17 cm (which I measured), Cd = 0.8, air density = 1.1 kg/m³, I can calculate the effect of a 5.6 cm drop in head position on power, assuming power depends on frontal cross-section and the head down allows more of my torso to draft. The result: 6.7 watts @ 45 kph. Chasing to close gaps i...