Originally Posted by
gerundium
25 mph ~ 40 km/h -> 40/3.6 = 11.11 m/s
assume a rider + TT bike setup system weight of 70 kg.
Crr of 0.004 for some smooth rolling roads
and a CdA of 0.2 (that's a really dialed position already! world-class could be a bit lower)
air density 1.25 kg/m^3
g = 10 (easy mode)
0.004*70*10*11.11 + (1/2)*0.2*1.25*11.11^3 = 203 Watts
aforementioned 200 Watts at 40 kph is about the lowest you can expect. If you are a world class pro on a world class setup you can get it lower somewhat but that's scraping the edges of marginal gains.
I apreciate the calculation, but got a measurement? I ask because I have seen many posts about power, and many strava power posts that just seem slow to me. I'm a near 60 really big (fat) guy and I turn 20 or 25 (not so much 30) at power way lower than most post about. I asked my kid about power to hold 20 and he was not nterested and said under 150W easy. I do have some numbers from the past, but it is hard to do a lab test on the unwilling.
Anyway, we post so much about power, and not so much about speed from how little power, I thought it an interesting question/exercize.