I'm putting together a bike for a friend. I have a 27" front wheel here, with deep, straight sides. As I was cleaning up what appeared to be glue, I began to wonder. Could it be a tubular rim. Unmarked. Old. Concentric grooves in the rim wall. And upon close inspection, unhooked. But much deeper profile than your standard tubular rim. Can I trust a clincher on it?

13,516 posts, including 173 photos but no photos now?

The "glue" is, possibly, rotted gum wall rubber.I have seen it many, many times.

Could also be adhesive from old and long-gone rim tape, if no rim tape is present currently.

Someone please correct me if I’m wrong!

There are no (production) tubular tires larger than 700c (622). We are talking modern era - post-WWII.

edit: or tubular rims

The hub is Magistroni. Spoke lacing is four cross. I likely picked this up from a friend who lived in and toured Europe, with his wife, multiple times in the 60s and 70s

That is definitely not a tubular rim.
That fact does not mean that no one ever tried to glue a tubular tire on to it.
I might try a low-pressure wire bead clincher on it if I were emotionally attached to the wheel for some reason - maybe ride it in a parade or something; nothing more than that. For that matter you could put on an unglued tubular and ride in the the parade too. So many options!

That is a clincher rim through and through. Looks like an old gum wall tire got melted to it from sitting forever.

Thanks all. I just haven't been in the field long enough to be familiar with hookless rims. I jettisoned it shortly after the initial post, and replaced it with a 622 wheel I had around. Whatever got cleaned out was probably as mentioned--and old rim strip or melted down sidewalls. It came off strikingly easily with a rotating wire brush. What is history of hookless rims? Makes sense that wire bead would be the answer.

The hookless, wired-on tyre and rim dates back to 1892 when Dunlop bought Charles Welch's patents. Dunlop had invented the pneumatic bicycle tyre in 1887 but was in a tyre war with three rivals, all having different tyre designs. Dunlop's original design had used a tyre that was cemented to the rim using flaps that extended over the rim. Welch's system of two continuous wire hoops encased in rubber beads greatly facilitated mounting and repair.

At this point the story diverges, depending on the market. In Canada and most of Europe, the wired-on tyre was the preferred choice for the non-competitive cyclist. However, in the USA, there was no clear winner until the bicycle industry crashed in 1899 as result of market saturation due to increased competition. With the tyre companies suffering cash flow issues, the Rubber Goods Manufacturing Company took the opportunity to acquire the American patent rights for three of the four major players in the tyre industry, including Dunlop's wired-on. They effectively killed the wired-on, instead promoting the single tube tyre, which was cheaper and provided better long term profits. The single tube tyre used an inner tube that was vulcanized to the casing, which was then cemented to the rim, There was no method to remove the inner tube for repair, instead relying on plugs, glue injection or returning the tyre to the bicycle shop for vulcanization. The wired-on would not regain significant market share until the maverick Schwinn company re-introduced them in 1933, in balloon tyre form.

Hooked, wired-on rims started appearing in the 1970s with the introduction of high pressure tyres. However, a definite trend started with the 1976 Mavic-Michelin collaboration to introduce high performance 700C as a sports bicycle alternative to tubular rims and tyres. Hookless, wired-on slowly lost market share from that point onward but can still be found on some entry level and children's bicycles with medium pressure applications.