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Japanese steel KAISEI for a frame - looking for info

Larger diameter head tube will be stiffer and make the steering of the bike faster and more agile.
Some folks find steering with such headtubes twitchy though. Mostly though it'll depend on the builder and his philosophy on how the bike should handle.

Makes sense. Thank you.

... and indeed I see advantages of threadless headsets. But some of the criticism puzzles me.

No doubt threadless headsets have adventages, but how can you have a classic road bike without quill stem? Besides, correct me if I'm wrong, but a threadless stem and fork can be installed with a help of an adapter, if needed in the future.

And the criticism of Jobst Brandt sounds a bit overboard, doesn't it. :)
 
No doubt threadless headsets have adventages, but how can you have a classic road bike without quill stem? Besides, correct me if I'm wrong, but a threadless stem and fork can be installed with a help of an adapter, if needed in the future.
I have one here, they are really fugly but yes, let me know if you need one.

Who has been troubled by such a radial movement? (By experiencing it, not just by reading accounts of it.)

He means (presumably) , that the only input into steering is through a device that is attached in the center of a pipe (hence the radial reference) and that fit is not perfect, it can't be otherwise it wouldn't slide in. think about how many places a quill stem actually touches the top of the steerer tube, that place is the sole steering input. The less than flush fit was a moisture trap requiring frequent strip downs and rebuilds. No such problems on threadless. Stems could often get twisted in crashes, I have seen more than one racer jump back on his bike after an off with the bars straight only to crash again due to his forks pointing due left. Aesthetically the quill stem screams classic but for mine I would sooner have function over form, I learnt that the painful way from Campy Delta brakes.
 
Now, when we discussed headset options, we did talk about both options. He actually suggested threadless together with a carbon fork, but in the end I decided to go with the threaded as I want a steel fork and a classic look overall.
Okay, you most certainly have 1" retro.
 
I have one here, they are really fugly but yes, let me know if you need one.

Thank you for the offer. I think if I build a classic it will stay classic. And if that doesn't work for whatever reason (it's been about 20 years since I rode a quill stem road bike) I still have ny old reliable Trek :)

Here are the details of the head tube -
Diameter - 31.7mm
Fork steeler - 25.4mm
Internal diameter is 22.2mm.
 
Which end of the tubing does Kaisei mark with the paint? The long end or the shorter butted end? I've got a set of 4130R ready to be mitered, but would not want to cut the wrong end. :)
 
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