Make them larger than 27.2mm in diameter.

Other than the aero claim, I've heard the compliance claim.

Am I convinced - maybe yes, maybe no. All I know, based off a small sample size - the harshest riding bikes I've ever been on (all with 28mm tires), had D shaped/complaint seat posts. Maybe they were doing something to ease the ride quality of the bike? If that's the case - they were invented because of how harsh the bikes actually rode.

Larger = more material = more weight

This will come as some surprise to Klein and Cannondale.

Is that really the case? A seatpost only needs to be strong in the front-back direction. Indeed Thompson seatposts made use of this principle and made the internal thickness thicker in the front and back sides and thinner on the left and right. An oval seatpost is actually stronger than a round seatpost in the front-back direction.
Now if you were arguing that the Giant D-Fuse seatpost is weaker then I would agree with you. Their D shape definitely weakens the backside of the post.

let's not forget that a lot of aero testing is done with a rider in place

and that aero bike socks probably have more real impact than a round or oval seat tube

beyond that is seems like OP is working hard to make a discussion where there really is not a lot to discuss

Good point. Does "strong" = "rigid"? The D-shaped seatpost is intended to be less rigid in one particular direction, but that doesn't mean it's prone to failure, with is another way of thinking of weakness vs strenght.,h

OK, we’re getting some interesting answer. I haven’t thought of that angle. Is that so?

Maybe it's raining where he is.

Since you're a physicist, I'll answer your question the same way I would have answered one of my students; what are the properties of a tube (round or oval) that determine it's strength?

An oval tube in isolation is more aerodynamic than a round tube. But when you put a cyclist with his bobbing thighs in front of the seatpost thrashing the air into a turbulent mess, it's possible that that advantage no longer matters.

Engineers and designers need something to do, so under the guise of "improvements" they design and produce all kinds of new things, most of which do not matter to most recreational riders. I consider myself an avid cyclists who rides frequently and who owns a few modern bicycles which feature most of the new designs (carbon fiber frames, internal cable routing, disc brakes, tubeless tires, to name just a few). All these improvements came with the bikes and I had little say in what they were. I was fine with bikes that were built forty years ago as I am fine with the ones that are built today. Manufacturers produce new designs to get cyclists to feel that what they own is not as good as what they could own. If you are not a professional cyclist you are a recreational one, and as one probably do not need the latest designs however much they represent improvement. I've always enjoyed the bikes I've owned, and if I buy anymore new ones, I'll enjoy them too.

I find it difficult to believe that an oval seat post has any measurable advantage over a round one in terms of speed or saved power.

Close though not exactly. I’m “resting” for an event tomorrow. (And work is slow on a Friday)

As I’m on the market for a new bike, naturally curious about all these new “developments”.

jackb, agree. I’m quite happy to take most of these new design features, even if some of them are only marginally helpful. But we’ve also seen some rather bad test-of-concept features that didn’t stood the test of time.

So, which of the two statements is incorrect?

propagation/distribution of stress.

Meaning your statement could be technically correct, but it could be irrevelant because as njkayaker said:
Ultimately what matters is the aerodynamics with you on the bike. Aerodynamics of the bike without a rider is not meaningful

I'll rephrase the question: How do the material properties, the shape, and the dimensions of a tube affect the strength of the tube, and what properties can be changed by a designer to vary the strength of the tube?

Just to be clear -- my two statements are correct, but you (?) and njyakker are calling them BS? That's funny, because those two statements are the foundation of your argument that there is no discernible effect.

In the real world with a rider? Who knows!

You called a "real" effect, with no indication at all what you mean by that.

Most people are going to interpret "real" as being measurable.

Instead of being uselessly ambiguous, you need to indicate the watts that are being saved.

It appears an aero frame saves about 5-20 watts at 45 kph. It seems likely that the seat post is going to be a very small fraction of that.

Narrower handlebars appear to save about 5 watts.

https://na.rule28.com/blogs/r-d/the-...ly-in-upgrades


It seems likely the main reason the post is "oval" (they aren't actually oval) is to fit the non-round seat tube.

This is just dumb. No one has any idea what you mean by "real" and you don't provide any indication of what group of people it would be real for.

Given you are supposed to be a teacher of some sort, I have to say you’re a very ineffective one. You make numerous posts on this site, yet very little actual content was contained in those posts. Little information or knowledge shared, few points made with sufficient supporting evidence.

That would be a good note if not for the fact that oval seatposts, which invariably have the major axis running front to back, are inherently vertically stiff and laterally compliant.

You are arguing without actually differing.

This was simply restating tomato coupe's point.

When the student is ready, the teacher will appear.

You made a couple declarative statements that appear to be in error. For example, you said you can't make a larger diameter tube of the same strength without more material, but in fact you CAN make a tube stiffer by using the same mass of material to make a tube of larger diameter. This is why Vitus aluminum bikes are noodly and Klein and Cannondale aluminum bikes are stiff - larger tubes with thinner walls - same mass, larger diameter, stiffer tube. It's also why most modern steel bikes have larger diameter tubing but are lighter than older steel frames.