Have been looking in to the BK for a bit and was curious about wtf Deda com12.5 is. There’s no reference to it on their website. The design has been around for a while now so this might well known to everyone that cares, but it was news to me. Found out from the Deda US distributor that 12.5 is Deda Zero Uno. It’s their “distance” tubing and features an .08/.06/.08 profile for most DT diameters.

Way thinner than I would have expected given the frame price. Anyone know the diameter of the DT?

I think the DT is 28.6mm, same as the seat tube. It's just CroMo tubing.

Nope. Down tube has a diameter of 35mm, top tube is 33mm. Seat tube has an OD of 30mm, just like most steel frames that take a 27.2mm seatpost.

Also, the tubing info has been listed on the Retrogression site for several years.

No doubt. The trouble is finding out what com12.5 is. Unlike Reynolds 725, for example, com12.5 is not listed in any modern Deda product lit and hasn’t been since at least 2005. Finding out how it compares to other steel was a challenge, and the reason for the thread.

Thanks for listing the tube sizes. Super helpful!

Typo?

30.0 - 27.2 = 2.8 / 2 = 1.4mm wall. Pretty thick for a steel frame.

In any case most quality 27.2 ID steel seat tubes are 28.6mm OD (1-1/8") with a 0.7mm wall.

If it's aluminum, the likely OD would be 31.75mm (31.8)

Probably externally butted ST, with a 30mm OD at the top, and less below that point.

Generally they would neck it down at the top.

Since the ID is fixed at 27.2 to take a post and a wall of something to either side of 0.7mm, so it might be a 30.0mm tube, necked down to something roughly 28.6mm. The math doesn't always work because necking tube down, might produce a slightly thicker wall. (this is controlable with mandrels so it's a design consideration, rather something that just happens).

Necking a larger tube down to accept a standard post is common with Ti frames, and suppose is possible in steel, but 30.0 doesn't conform to any of the classic standards. Also, it's a decent amount of work and added cost for such a small change in OD. But that said, I'm not in touch with some of the creative stuff happening out there.

No typo.

My Bare Knuckle's seat tube OD is 30mm at the top and tapers down very slightly to about 29.8mm below the external butting. My wife's Soma Rush is the same, as are the Pake Rum Runner and All-City Big Block. And yes, I just measured all four frames.

Edit for the record: The MASH Work, Affinity LoPro and Surly Steamroller take a 30.0 collar too. Go figure...

Yes, see the post immediately above yours where I described necked down tubes. (2 up from here)

However, I didn't ask in reference to this frame, but because of your reference to, "just like most steel frames that take a 27.2mm seatpost".

As I said, MOST steel frames with 27.2mm IDs are straight 1-1/8" OD (28.6mm), but obviously not all. Which is why I asked if it were a typo, giving you a chance to elaborate.

Not worth fighting over, just a minor point.

See my edit above. Every steel frame my shop has in stock right now that takes a 27.2mm seatpost has a seat tube with a 30mm OD at the top. Not "most". Every. Single. One.

If you knew the number of 28.6mm seatpost collars customers buy from Retrogression, then immediately send back in exchange for 30.0 because it didn't fit whatever steel frame they have, your head would probably fall off your shoulders. We've actually considered not selling that size at all.

Fun fact: Even the beloved Kilo TT - which takes a 26.8mm seatpost - needs a 30.0 collar.

I thought it was made of choco tacos