Take away all psychological factors, including that 100 or 160 km are round numbers. Also take away that a bike is a transportation device (and hence training for 160 km means one can visit towns 80 km away by bike). What is left is purely the physical advantage. What does someone doing 80-km rides gain from doing 120-km or 160-km rides?
Runners take special pride in the length of their greatest accomplishment. They might intone "I've completed half a marathon," or they might sigh with a hint of humility "I have yet to run a full marathon."
- Running 42 km is not "just" more arduous than running 21 km. It leaves the human body in a special (better, healthier, ..) kind of shape, or it takes a special kind of preparation to achieve the milestone.
- It doesn't quite matter how fast the course was completed, just as long as the speed resembles running more than walking.
Likewise cyclists will boast "I've completed a century," and perhaps qualify it "metric, not imperial."
What's so special about riding 100 km in a single ride?
Context: I ride 80 km once a week, plus two shorter rides mid-week, and I'm gradually making my way towards 100 km, but I'm not sure what it means, besides enjoying more time on the saddle. I am basically looking for motivation to continue increasing the length of my rides. Completing 100 km or 160 km does make it possible to join clubs that ride for these lengths, but let's dismiss that social factor, in particular since those riding longer distances seldom slow down enough to actually chat. These are definitely keep-up-or-get-dropped rides.
Is the answer identical to the accepted answer at the following question?
In other words, do the benefits of base kilometers not max out at some point? Does, for example, riding 100 km on Saturday and resting on Sunday make you a better athlete than if you rode for 50 km on Saturday and then rode again for 50 km on Sunday?
Chris H says:
If you can ride 80km in a day, [..] you could quite possibly go out and do 160km [tomorrow], [..] but you'd be quite likely to suffer for it.
I am most interested in this closing sentence: “but you'd be quite likely to suffer for it.” If I will suffer after doing 160km tomorrow (despite sufficient nutrition and hydration), but I will not suffer from 160 km provided I work my way up to it, then this means that something changes in the body when one trains for longer distances.
The reason cycling breaks away from running is the following. It may, just may, be the case that only a subset of humans have the genes to run 42 km. But anyone, with training, can cycle for 160 km, again with training. If true, it would be a huge boon to cycling. It means a cycling trainer can tell a budding cyclist:
Unlike running, you do not need to have a genetic makeup that is proto-Olympic. You can cycle 160 km, if you just train for it.
But a running trainer, faced with the aching joints and the limited lung capacity of an aspiring Boston marathon participant may turn them back and tell them “you’re simply not made for it.”