"On a clincher, changing the rim width changes the radius of the casing arc, but it doesn't change whether it's circular."
I suspect this isn't quite accurate. Carry the thought out to an extreme... if the rim is so wide that the tire can bare be mounted on it, it will be little more than a flat rubber/cloth membrane spanning the rim. As you widen the wheel to approach that entirely hypothetical state, the tire will gradually be less circular in section than shallow U shape.
At any useful state it would be rounded, but I don't know about "circular."
The extreme case is perfectly valid: the casing will be a large-radius circular arc. This is unambiguous. Any other shape would require a much stiffer casing with nontrivial bending stiffness.
The shape of the casing is not the pertinent thing when it comes to aerodynamics
I'm not sure how to make this any more clear: I'm talking about the shape of the casing. You're talking about the overall shape of the overall shape of the tire, which is the casing plus the tread. Differences in tire tread profiles alter the overall shape of the tire to a very small degree, but that's still enough to matter for aerodynamics. No one is arguing otherwise.
it's the shape of the tire, which could conform exactly to casing shape or could be quite different based on whatever is glued or vulcanized to it.
The tread would have to be relatively stiff to change the shape of the inflated casing. A tread stiff enough to do this would have tremendous rolling resistance. Don't forget that the tread is an elastomer, and elastomers creep like crazy. Even if the tread were stiff enough to distort the casing, it would relax with time and the casing would tend to return to a circular state.
From the years Iv e spent worrying like crazy about attached flow on sails and leading edge issues that trip the flow
Worrying in what capacity? Were you worrying because you were close-hauled, beating into the wind and hoping to bear up a little more? Or were you worrying in a professional capacity? If the latter, what kind of professional capacity?
there may be something to the idea that Conti gets an advantage from tread, but... the advantage seems to be pretty large for it to be mainly the surface texture of the tire, it seems more likely to be tire shape...
Michelins and vittorias have done pretty badly in the tunnel and if it were simply a matter of molding in more texture they and others would fix it quickly...
You'd do better to point out that most Vittorias have a lot of texture while Michelins usually have none. You seem to think that Continental has somehow controlled casing shape to be non-circular. Do you think so? If so, how do you think they did it? (Hint: their casing plies are at roughly the same angle as everyone else's).
But you've posted some interesting and useful stuff, I want to go back and read through the stuff you point to... Thanks for a thoughtful post.
Thanks; I'm glad you find it interesting. I do this sort of thing for a living (though no longer in the bike industry) and it's fun to apply my professional skills to my hobby. When I was racing as a junior, I didn't know anyone who knew why disc sew ups gripped the rim more at higher pressures, let alone why one pedal had left-hand threads. I'd be pleased if some people found this stuff useful, or at least interesting.
Edit: Damn you, autocorrect.