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BigPoser 08-16-19 02:44 PM

Seat tube wall thickness
What's a good wall thickness for a ST that is good for a fillet that will help reduce warpage at the top tube? I fully understand that heat controls rules all, but I still want to be a cautious as possible. 0.9, 1.1, 1.0? What works best for a happy medium?

Thanks in advance.


Andrew R Stewart 08-16-19 06:07 PM

Part of the issue with the ST/TT junction is the binder for the post. Too thin a ST wall and you get stretch city and the slot can close up more easily over time. Especially if you're a tad undersized on the post diameter dur to distortion and a reluctance to ream because of the thin wall. (Like the flow of events?:))

For a skilled builder a .8 or .9 wall might be a practical min at this junction. But I would feel far better with a 1.1/1.2 wall on an externally butted tube. Andy

dsaul 08-17-19 06:39 AM

I always use external butted seat tubes with 1.1 or 1.2 mm wall thickness. The thickness depends on what brand tubing I buy and not a personal preference for either. The only issue that I've found with using external butted seat tubes(for 27.2 seat posts) is the very limited option for 29.8mm seat post clamps. The only options I've found are Thomson, some Chinese ones on Ebay(Zoagear) and I think Nova sells one. There are a few QR clamps in that size, but I don't consider them a serious option.

calstar 08-21-19 11:24 AM

Originally Posted by dsaul (Post 21079411)
....There are a few QR clamps in that size, but I don't consider them a serious option.


dsaul 08-21-19 01:39 PM

Originally Posted by calstar (Post 21085742)

I've never seen a QR clamp that worked as well as a bolt on clamp. They always seem to allow the seatpost to slip. I just don't see a need for a QR clamp on anything but a rental bike. I would never put one on a bike that I own or a frame that I build for someone else.

calstar 08-21-19 01:54 PM

See above. Ok, I get it, you're talking about the non brazed slip on clamp, not a brazed barrel or tabs using a quick release lever, and not a crappy open lever like the in the pic but a closed over cam type.

duanedr 08-24-19 02:35 AM

I have used a few externally butted ST but, my preference is to use a seattube that is butted with a seatpost end with 0.6mm walls (28.6mm for 27.2mm post). Then, I add a roughly 1mm thick sleeve (0.058" turned down to 0.040") which brings it to roughly 1.6mm wall thickness. There is also another 0.25mm or so of filler material.

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