Originally Posted by
hamster
Re-read the starting post in the thread. The person is complaining about being unable to go faster than 10.1 mph even during 2-3 hour rides. My power data has me at 87% FTP for 1h50 and 71% FTP for 3 hours (and I can probably do better than the second number).
Further, the calculation assumes that he's pedaling all the way downhill at constant power. Let's make the model more realistic. Suppose that he goes up hills at 145 W, on flats at 100 W, and coasts downhills after getting up to terminal velocity. That only drops his average speed to 12.7 while dropping his average power to 104 W.
Finally note that my route profile has 70 ft/mile of climbing, which would be pretty hilly even by upstate NY standards.
Consider how flat the CP curve is in the region beyond hours. That only distorts things by a small amount, perhaps 10%. At least that's what my data shows, anyways. It's possible your FTP could be underestimated. That's not a rare problem.
I mentioned the ultramarathon limit mostly because that's the number I have been most interested in, and have the best handle on, and would be the limit of interest to a person completing a 200K, as was referenced by the OP as being his goal.
Aside from that, do you know the CdA and Crr used in that calculator? As you alluded to, therein may lie at least part of the OP's speed problem.
The rest of the discrepancy between your calculation and the OP's report speeds probably lies in his weight (bike plus rider plus crapola/baggage).