Ignore your teeth and they will go away.

From both your words and the title of this thread: "After how many miles a day do we get diminished returns with our fitness?"

"fitness" -- not "diet" or "weight loss".

Is the OP seeking advice on how to lose weight? I may have missed that.

If so, is your advice then: "Better not ride hard or long, or you might get hungry and eat too much"?

Thank you. Other than viewing this forum, hard to imagine many here have anything in common with Dreamy. :lol:

Well, the more 50 mile rides you do, the easier they become, the faster you go, etc. And the routes you ride can be chosen to build up, for example, your climbing ability. When I was building up for the one Century I've ridden, yeah, I rode longer and longer distances, but I also threw in more climbs on Sunday long rides and hill intervals on weekday rides. It seems to me one can train for any athletic event, not just competitive events.

once you've exhausted all your tubes & spent all your water for the ride, it's no longer fit to ride.

I think you're assuming you are the norm here. This is a classic ymmv situation.

Maybe it's just a perspective thing, I've been riding dozens of centuries per year for the past 4 years, so they really do just seem like longer versions of every other ride I take rather than an event. Also, I think in terms of working out, which is aimed more at general health than training, which is aimed at maximizing performance at a particular activity.

I've had some rather unfortunate centuries where I actually had to stop and buy tubes more than once.

if i blow through the spares on-board, I'll take that as a sign & return to the duty station.

Where were you when I was ten years old and pouring sugar all over my frosted flakes?

They make these things called 'patch kits.'

Things like that always occur on the return leg. Basically, it was then I learned my 23 year old wheel was not salvageable.

I'm aware. I hate patching, so you can have mine.

The wheel was mysteriously causing the flats. It also was snapping spokes right and left and going out of true right after being trued.

You don't train for a marathon by running a marathon every day.

Remember the old names? Sugar Frosted Flakes. Sugar Corn Pops. Sugar Smacks.

The guy who used to voice Tony the Tiger sang “You’re a Mean One, Mr. Grinch.”

You might not train for a marathon by just doing halfs either.

Bicycling on-line suggests the training plan I successfully used for my first century many moons ago, https://www.bicycling.com/training/a...ide-a-century/

OP, it depends on so many different variables it would be hard to quantify. Age, aerobic capacity, starting level of fitness, do other endurance sports (like running), ratio of fast to slow twitch muscles, internal drive, ability to endure discomfort, and on and on. Grand Tour riders supposedly get stronger the further they get into the event but don’t know how that can be quantified. Physiology, mental toughness and training are keys in endurance sports. There must be an article somewhere on the maximum stress an average body can endure on a reoccurring basis before going downhill.

Oh crap now you tell me! Can I do it virtually now like through google's map? This is how you run right?

Well you have to build up to it. So if starting from scratch, you might start with say 20 mile rides and once those feel easy, increase to 30 miles, then 40 miles etc, etc. Eventually you are able to do the 100 mile target. But my point was that this only applies if your end goal is to achieve a 100 mile ride.
I only mentioned 50+ mile rides because that's about the minimum distance you should be able to comfortably achieve before attempting your first 100 mile ride. If say you were training for your first 100 mile event (race, joyride, whatever) it would be advisable to complete at least one 75 mile ride beforehand. But you don't have to do countless high mileage rides - that would be inefficient. For example I do maybe half a dozen 100 mile events per season and will do maybe half a dozen 50 mile training rides and a few 75 mile rides and maybe one 100 mile training ride in the lead up to my first event.

Training just means preparing for whatever it is you want to achieve. It can be a race, fun ride or whatever other riding goal you have in mind.

So the best way to prepare for a 100 mile ride is just go out and ride 100 miles is it? Well that implies that you have already completed the necessary training to ride 100 miles. Nobody just gets on a bike and rides 100 miles without "training" for it in some form. The more accepted method is to gradually build up the length of your training rides to at least 70% of your target distance before attempting your final distance goal. (presuming that's what your goal actually is)

A marathon is a race. I don't "train" for a ride. I think it's the wrong word.

Also, there's no comparison between the amount of recovery needed after a marathon and that after a century. Even in racing, there's no runner's equivalent to a grand tour race, where they ride several centuries plus per week.

I've never run a marathon, but I ride a century once a week at the age of 60, weather permitting. I don't know anyone who runs a 26.2 mile course every week. They're not equivalents.

I won't go all Grant Peterson here and assert that calling this stuff training is ruining bicycling because, hey if it motivates you to ride more, call it whatever you like. Treating distance riding like it's a discipline would demotivate me,

Coming back to the original question. There is only really a benefit in riding more than 40-50 miles if you simply enjoy doing so or are training/preparing/conditioning yourself to ride those longer distances for whatever reason. If you are cycling only for fun and general fitness and you have had enough by 50 miles then there is zero point in riding any further. If fitness is your primary goal, then shorter, higher intensity rides are far more efficient in boosting your overall fitness level. Distance is only 1 dimension of training load.

How far is up?
How long is a piece of string?
How much do "we" weigh?
How tall are "we"?
What bike do "we" ride?
What is "our" average speed?
When are "we" supposed to wave?
(I'd like unanswerable questions for $600 please, Alex.)