Originally Posted by
ThermionicScott
Rules of thumb are imprecise by nature. This one is likely as much psychological/motivational as it is physiological. All but a small percentage of people on BikeForums could ride a century tomorrow if sufficiently motivated, but rules of thumb like this and the "you can ride 50% longer than your last long ride" help to rein that into something easier to plan around.
Tapering can be assumed for these rules of thumb...
I have no idea if people can do it and aren't sufficiently motivated, or if they can't. I'm under the impression that the vast majority of people on BF aren't particularly interested in the endeavor. It's easy for us who do them to say it's just a matter of motivation, but I don't want to assume that.
Yeah, I'll go with the "rule of thumbs" being more of a psychological motivator for people working up to a century than any reasonable estimation, because anything beyond that, and these numbers start to be absurd very fast. I did a 132 mile ride earlier this year, I guarantee I don't think 196 miles in a day is in the offing for me anytime soon.