Originally Posted by
merlinextraligh
The Kurt Kinetci numbers, IIRC are based on a 1% grade.
In fact, Kreuzotter an online power calculator, gives you 248 watts at 20mph, for their default rider, in the drops, and on a 1% grade.
Exactly how it correlates to the road depends on how aero you are, and how much you weigh.
For me personally, it a bit harder on the trainer to maintain 20mph, than on a flat road.
In the end all that matters about speed on a trainer is the extent to which you can use it to extrapolate an approximation of power.
FWIW, these numbers are a little lower but in the ballpark with my observations in the real world with my powermeter. In fact, I usually use 21 mph (no wind, flat road) as a rough equivalent for 250w when I am on my FG without a PM. But then as you say, a lot has to do with how aero you are, and I have a fair amount of bar drop and I try to focus on a flat back during these intervals.
The problem with trying to apply this to a trainer is that we have no idea how much resistance the trainer is giving. How hard is the the roller cranked down? I can set mine up so the at the roller barely touches the tire and then spin a 53x12 at 120rpm but is that 400w? Is it 150w? Who knows?