's Forum Archives - Retro - Classic Bikes

Archive Home >> Retro - Classic Bikes

Can the inside of a steel seat tube be slightly "widened"?(6 posts)

Can the inside of a steel seat tube be slightly "widened"?Tommy B
May 7, 2002 8:06 AM
Ok, I don't know if this is a crazy thought or something that can be done by an experienced person with the right tools (framebuilder?) Can the inside diameter of a steel seat tube be slightly "widened"?

I just bought an older ('72) lugged steel frame that was advertised to use a 27.2mm seatpost. I was doubtful that a frame of this age would use this more modern seatpost size so when it arrived I put my trusty vernier calipers to work... sure enough it's actually either 26.2 or 26.4mm. If I could get it "enlarged" slightly to 26.8 I could use the post I had in mind for it. I know that AM Classic and probably Thompson make sizes that will with but their look is not quite right for this frame.

Is this something any of you know about? Have any of you done it or had it done? Machining, filing, "rifling"???
I'm reluctant to try to just file it with a round file because I doubt I could get it evenly filed without screwing something up. Would removing .2mm from the wall of an older steel tube really compromise it's strength? (I'm 145-150lbs and this bike is not for racing). It's Columbus steel but I don't know exactly which type.

Any help, experiences and/or suggestions would be greatly appreciated! -Thanx
yes, maybe, no.......Spirito
May 7, 2002 8:58 AM
its better to try and find the right post. failing that i have doctored seat tubes to accomodate a 0.2mm difference but these were on frames that were beaters.

you might have to go with the voice of someone more knowledgeable on these things - anyone?

if you are stuck without option i might be able to help as i have an assortment of posts of sizes 26.4 to 26.6 of different vintages and styles - some new, some used. depending on condition they could cost anywhere from postage alone or up to $30.

Some informationNessism
May 7, 2002 10:40 AM
I'm not sure you can open up the tube as far as you want. An adjustable reamer can be used but it is not advisable to cut the tube any thinner than .6 mm. Keep in mind that it is customary to provide .2 mm clearance between the seat tube and post.

28.6 mm tube w/.6 mm wall thickness = 27.4 mm hole size (and 27.2 mm seat post)

And don't try to use a round file or the like - you are likely to damage the frame.

Sounds like I'm stuck with what I have (:-(Tommy B
May 7, 2002 11:44 AM
Thanks Spirito & Nessism,

Well, I wasn't getting my hopes up when I posted the question. I'm not sure what the tube wall thickness is now but I can see that if I needed to ream an extra .2 mm clearance between the seat tube and post, I might be pushing it to try and use a 26.8 post. I don't want to risk ruining this frame. I certainly wasn't going to attempt it myself.

I was planning on building this bike up as a fixed gear with almost all contemporary components (w/ polished silver finish), but with an elegant, "curvy" look to complement the pretty lugs: Deda Murex quill stem, Chris King threaded headset, Campy Pista (Track) crank, and a 26.8 Performance Forte' seatpost. I know, I know...most Performance brand stuff is not the highest quality but I have one of these in black and it's actually a great post. It's light and has a high quality finish. I think the tapered, slightly bladed post and two-bolt clap design are quite elegant despite it's no-name brand origins. It seems like it would compliment the Murex stem.

Campy made some slightly bladed "aero" alloy Record posts a while ago, didn't they? Spirito, do you have anything by Campy like this in 26.2 or 26.4? I might try going to a couple vintage parts websites to see what's out there. I have a feeling that since I'm looking for something in very good to like new condition I'll have a tough time finding one the right size or it would be extra pricy!

Any other suggestions are most welcome.
Sort of had the same problem...Lone Gunman
May 8, 2002 12:41 PM
Searched for a while and found a post that matched the rest of part of the Components (SR)and found one for $45. Needed a 26.2. Was at the LBS and they had a fluted aluminum no name new post for $20. The flute slots are painted black along with the top of the post where the seat is sitting and is micro adjust. Looks retro because of the flutes.
Just an update...Tommy B
May 8, 2002 8:42 AM
Well, I won't be trying to mess with my frame. I just went to and found the perfect post. They had a 26.4mm NOS/NIP Campy Record post and it has the narrow "aero" look that I wanted. I'm not sure when it was made but it looks like the one in this '97 Chorus Group. It was $65 but well worth it to me.

I think it'll look sweet with the Campy Pista crankset I'm going to use.

Now I just need to find the right size seat collar...hmmm...