Perhaps I should just go measure, but I don't feel like stripping of the grips of the 25.4 bars.

Thanks for your help!

Grip area is the same.

It has to be so that brake levers can be attached. There's essentially only one size of lever clamp.

ROAD bars are 23.8mm... MTB/BMX bars are 22.2mm.... in the "Grip Area" and where the controls clamp onto them.

Road bars vary in the stem Clamp areas... some are 25.4mm, some older ones are 26mm, and the large clamp area bars are 31.8mm...
there are other sizes, but they are either obsolete (like the French, 25mm) or for low end bikes.

MTB bikes have 25.4, 31.8, and now 35mm stem clamp sizes....

As a point of note, Deda have had their Trentacinque 35mm clamp area bars and stems for road bikes in the market for about 10 years, and they are neither obsolete nor low end.

after looking at a few of those online, i'll not be buying them any time soon... $130 to $200 for a stem... up to $250 for bars... etc.

i did notice an odd abundance of extremely LONG stems... 120, 130, and a dearth of 140mm stems... why is that?

the larger diameter upper bars would be nice to reduce finger curl cramping, but the larger tubing would tend to be too stiff and transmit excess road vibrations, i'd think (i've noted this with 35mm MTB bars, and to a lesser extent on 31.8mm bars)... do you have any experience with the Deda bars/stems that you could share?

I don’t think 35 pricing is any different than standard road kit, and in fact you could spend a fair amount more in 31.8mm. There is only Deda for 35 (I think), so it’s really a lack of options issue rather than a pricing issue.

But yes, I’ve been riding Deda 35 since ‘17 and really like it. Mostly it just feels affirmative and solid in the hands, and there is no sensation of the bar twisting about the stem. I don’t ride on the tops, the actual 35mm area, all that often, but yeah, it feels substantial and reassuring when I do. It looks the part, too!

As for shock transmission, I don’t notice anything harsh. Carbon Fiber is so much better than aluminum in that regard, I think it’s a non-issue. I have an Ibis alu bar on my winter/spring bike and it feels way harder and less forgiving despite being 31.8.

In all though, there’s not a whole in 35. It’s nice for me, but I can ride 31.8 just fine and without complaint. Were there the same options in 35 road as 31.8, I choose it preferentially, but there aren’t, so it’s just a quirky, niche thing. It was perfect when I did that complete, frameset up, build, but was not an option when I bought a complete bike, and no 35 aero option anyway, so that was that.

I see a number of reasons for the long stems, and they all have to do with customizing the fit of the frame to the rider. Before I edumacated myself on frame angles and design I never gave all the dimensions much thought. It's no wonder I was never satisfied with the fit of most off the shelf frames as they are typically too short in overall reach, which combines not only the published reach from vertical center of the BB to the vertical center of the top of the head tube, but also the rear reach to the saddle, based on the seat tube angle. Add to this the vast variance on bar design, the drop and reach, the need for large stem selection is surely warranted. It's not like 130-140mm and longer stems are a new thing, they've been around since I recall first riding Cinelli 140mm quills in the 80's.

From a pro rider perspective of being handed a team frame to ride, when frames were made of various metals, they were typically custom fit for a given rider. As far as I know, nowdays with carbon frames they are not custom fit, they're all off the shelf frames, so a given rider must make do with whatever geometry the bike has. The riders only option for fitting compensation is the bar/stem combo and seatpost. I've seen pro road bikes of riders like Michael Rodgers using a 150mm stem, and he's not all the tall.

that's a damn nice lookin' bike, C...
here's my feelings on bar sizes... road bars have been stuck in the sub-one inch size for WAY too long... they have been restricted to that dia, because of the manufacturers' resistance to stepping out of the norm and upping Control Clamp Sizes to a new standard... many might cite the Deda 35mm clamp experiment as a reason to NOT rock the boat.
many people double wrap bars... a person asked about the old school "sleeve style covering with holes in it" just yesterday, for a better fit for his long fingers... he has tried the squishy foam, and liked the size, but HATED the squishy foam itself... same goes for double "cork" wraps too.
i'm not tall, and use Oury grips on my flat bars , and double wrap my road drops... there is an abundance of rough pavements in my area, and some flex in the bars saves me from feeling like i'm hanging onto a paint shaker on the bike paths and gravel roads.
MTBbars are even smaller in the grip zone, but there are options for extra size with grips like my preferred Ourys, which also give vibe-reduction.
one customer has had me looking for a Earlier version of my gravel bike, just so he can have the advantage of the more curved fork on those Sirruses... he rode a friend's Early Aluminum Sirrus and knows there is a difference in compliance.

Garthr.. the long stems i mentioned are for sale on Ebay... this means folks are dumping them for shorter stems, or just didn't like the 35s, in general, for other reasons, IMO.. possibly the lack of drop or shape options in 35mm bars, or added shock transmission....

personally, two of my road bikes (Trek 930R custom and the Gitane Crit bike) use goosenecks, so they can't use the 35mm design... and the Fuji is currently fitted with 25.4mm clamp to help suck up some of the pavement quakes...