Well ... first, that is not diminishing returns .... that is overall weight.

Second, and this is something that also matters a lot imn auto racing ... having a very light frame enables the designer to adjust balance and strength by reinforcing/ballasting at different places. On a bike frame, where to ballast is not so critical (it pretty much goes in, on, or around the BB shell.) With a car, lowering and tailoring the position of the center of gravity is really important to handling. The bike just needs to have enough lead tacked on the make weight.

But for the guy designing the bike frame, he is told, "Here, put this relatively heavy battery somewhere." Having a frame which is two ounces lighter makes it possible to meet the minimum and include the battery.

When everyone goes to disc brakes, there will be more weight added ... so again, the lighter the frame, the better.

But even so, the folks designing the bikes Chris Froome and Peter Sagan ride (I think) are not even that concerned about overall weight, because they know that can build a 680-gram frame or whatever. They are looking at things like aero, directional strength, localized stiffness ... basically building enough rigidity and flexibility into the bike to increase performance through frame engineering ... basically what tube-makers did with double- and triple-butting, hydroforming, and I forget the latest technique, but that stuff.

Diminishing returns would be, the bike frame is lighter but it cost so much to build (or replace when it breaks) that the manufacturers cannot afford to sponsor teams, or if the lighter frames produced no advantage ...

And of course the whole "Lighter Frames" thing is a red herring, because CF isn't just about being light. CF is about having the ability to create almost any shape with any characteristic, so that the bikes can be lighter and stronger and more aero, and stiffer and also more compliant in different places.

Another thing to consider: Racing machinery is built to fail. People designing racing gear couldn't care less about "lifetime warranty." If the vehicle gets the rider/driver to the finish line first, it is a successful design. If it falls apart ten feet past the finish line, who cares?

Racing eats up components. I have heard a lot about how Dura-Ace isn't really worthwhile for a daily rider because it is designed to last for one season of racing and be replaced. Whether or not that is true, or to what extent, is irrelevant; the idea is accurate. Things built for racing are made light versus long-lasting. And things made for racing are made to be and are treated as, expendable. Frames, tires, wheels, other components ... use 'em up, toss 'em.

Have you ever seen how many sets of tires an auto racing team will use in a weekend? The tires are only good for a few hundred miles, and often only really good for a fraction of that. Does this mean rubber tires suck? No, it means tires designed for racing are not built to last.

A CF bike used in racing is designed to be expendable, because the teams expect crashes. They simply don't care. The teams don't have the time or the resources ready to rebuild frames---just grab another one from the van and let's go. So the fact that bikes (of any frame material) get abused and discarded in racing pertains only to racing.

For the kind of casual road-riding that most of us probably do, the rigors of racing are about as important as the performance of racers. Chris Froome is probably faster in his sleep than I am on my best day on a bike. It has Zero bearing on my life, or my ride. He might go through seven bikes in a Grand Tour. Means Zero relative to me.

I want to build a CF bike so I can have an affordable bike which weighs about 15 pounds ... affordable on my budget, of course. I also like building bikes, though I am not very skilled ... another thing Mr. Froome and I don't share (pretty sure he doesn't build his own bikes, eh?) I don't need a bike that light; it certainly won't make me any faster. But I will enjoy owning and riding it (if I build it right) and that is what I plan to do.

Basically, what happens to racers means nothing to me. And frankly, what happens to the bike in a catastrophic wreck means nothing to me too .... because I don't plan to be involved in a catastrophic wreck, and if it happens anyway, I am mostly concerned about my survival, not the bike's. So when I shop for bikes, I only think about My ride ... not some potential wreck, not what some WorldTour racer does, none of that.

When people come here posting "proof" that some frame material is better, it is humorous because apparently those posters cannot see that context determines what is "best" for each rider---there is no absolute, except that the bike must be ridable when in riding trim (i.e. when not wrecked or asploded.)

When they post "proof" that a given frame material is hazardous--like Al, Ti, and CF reputedly are---it is sort of like "proof" that Bigfoot exists. it is great to state an opinion, but having three people echo your opinion equals zero proof.

It is a little annoying and a little amusing when people come here posting, essentially, "Let me think for you because I know better" and then demonstrate an inability to think well. Not that they are stupid, just blinded by their own prejudices on certain matters.

To sum it all up---IF YOU RIDE CF YOU WILL DIE. This seems to be an absolute truth and one upon which we can all agree. Same as if you never ride CF. But then, I might go and live forever and shoot down my own argument.