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PostPosted: Sun Sep 15, 2019 11:34 pm 
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I've got a fully built 93 (I think) frame which takes a 27.0 post iirc. I have another frame which is a later vintage, though not sure what year exactly, but it has curved seat stays which my built bike doesn't. I'd assumed the seat post size was the same, but it's way bigger than 27.0. I've tried various posts that I have laying around, none fit. All I can conclude is that it's much bigger than 27.2 and smaller than 30.9.

Anyone know what size post it should take?


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PostPosted: Mon Sep 16, 2019 5:45 pm 
retrobike rider / Gold Trader
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Has it still got its shim bonded in the seat tube? I had a ‘95 (with the curved stays) that took a 27.0 post and 31.8 clamp and derailleur.


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PostPosted: Mon Sep 16, 2019 6:05 pm 
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No shim inside the seat tube on my one.


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PostPosted: Mon Sep 16, 2019 8:01 pm 
retrobike rider / Gold Trader
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I’d say it should have one. All my titanium frames have had one bonded in by the manufacturer.

Doesn’t your ‘93 have one?


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PostPosted: Mon Sep 16, 2019 11:23 pm 
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I cant remember if the 93 has one, but I've a few other ti frames that don't have one (more modern). Does it need one? What's the reason for them aside from defining the post size?


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PostPosted: Fri Sep 20, 2019 10:59 pm 
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Location: It's not easy being a dolphin.
Can confirm. Should have an AL shim and take a 27.0mm post.

This could actually be a blessing in disguise. I would measure the ID of the raw seat-tube and
find an appropriate shim to 27.2mm. The FD is 31.8mm, so assuming 1mm wall thickness (max!)
we are in the 30mm territory, so shim would have about 1.5mm wall thickness.


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PostPosted: Fri Sep 20, 2019 11:51 pm 
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Thanks. Is the shim necessary? If the tube conforms to a known post size would it be a bad idea to simply use the right sized post?


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PostPosted: Sat Sep 21, 2019 1:05 am 
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Im just in the middle of a Axis TT Build from what I believe is same year, mine has the shim bonded into frame, takes a 27.0 post, i'm not going to faff with the shim, it must be there for a reason. The wall thickness on the seat tubing looks very thin IMO and I wonder if the shim is there to reinforce around the joint?


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PostPosted: Sat Sep 21, 2019 8:25 pm 
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Location: It's not easy being a dolphin.
My "guess" with limited knowledge is that the shim only serves to resist any chemical corrosion interaction
with whatever seat-post is inserted (at the time, probably AL was the popular), nothing from a structural point. The depth does need to be in the 80mm ball park though. Unlike the Hei Hei, there is virtually sod all
seat-tube extension above the top-tube / rear-stay joints so I can't see anything cracking; especially since this is top-notch Ti from arguably the best Ti house at the time (and ever?)

Better to waste an AL shim through any chemical interaction, than say have a seat-post permanently bonded to the frame. A suitable AL shim with copper paste would be the way to go IMHO. Then insert whatever floats your boat. Rough guess something like a 30.4mm?


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PostPosted: Sat Sep 21, 2019 11:37 pm 
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Thanks, helpful as always. I'm actually selling this one, so looking to provide as much info and help to the buyer, ideally a seat post/shim with the frame, but at minimum the details needed to source what is needed.

So I'm clear, the alu shim prevents alloy posts (or any material?) Bomdimg to the ti? What's stopping a post bonding to the alloy shim, which if I understand correctly, is glued in.

Every day is a school day.


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