Originally Posted by
RChung
The closest is that a 42 min 10K run is occasionally cited as roughly equivalent to a 1-hr 40K TT.
I got into a friendly argument with a guy on Slowtwitch who claimed duathlon 3:1 ratio had to do with equalizing the metabolic costs of run/bike. He claimed to have some kind of link to USAT. I disagreed with him because metabolic cost ignores physics of time gain running being largely linear, and time gain on the bike being very non-linear. You can measure "run power" these days. I found one of the super popular run scientist guy's pace/power calculator and then worked the math out on how long you would need in the bike leg to make time gain/loss on power differences in each pay out fairly. The 3:1 ratio wound up being pretty BS. It took even more than the triathlon 4.3:1 ratio to even out. Making the duathlon almost largely a runner's race with an annoying bike ride tossed in.
In other words, making 25w more in the run got you a LOT more time gain than 25w more in the bike.
As to the above, I don't train running "much" compared to bike and I have my run threshold set based on 10k distance at about 7:05/mi. My 40k TT time is a bit under 55min.
I do feel racing a 10k feels more similar to a 40k ride. You feel like you're easing into the pain a lot more than you do for a shorter 5k run or 10mi TT bike. I just detest those distances personally as it's just all teeth grit the whole time. A 40k TT sure does suck longer than a 10mi TT, but you ease into it a lot longer pain wise. Like the "boiling a frog slowly" phrase.