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Old 01-15-10, 07:20 PM   #1
Rudomanski
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23.8mm Seatpost Dilemma

Hi All,

I recently bought a 1987 Peugeot Corbier Frame which came with fork, stem, and crankset. I am pretty much set restoring this bike, although I just realized after searching the net for hours that the seatpost size (23.8mm) is abnormal and very hard to find. I've come across many posts of people with the same problem, but not any solutions that seem feasible. The best solution I found was the 24mm post custom made on yellowjersey.org, but this costs $70, and I'm really trying to keep this a budget project (paid 25 bucks for the frame).

Many people seem to say shimming a 22.2mm is the best solution, but even those posts with a rail mount on top seem tough to find, and shims that fit this also don't seem to exist. The soda can shim solution seems to be popular, but is this safe, and will it hold up to daily aggressive riding? Any other safe budget solutions are welcome.

Thanks in Advance,
Zach
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Old 01-16-10, 12:31 PM   #2
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One solution is to pull an aluminum alloy 24.0 post off another old French bike and file it down to 23.8, which entails removing just .1mm off the radius, easy to do by hand in about 1/2 hr.

If you've got a local resource with a lot of cast off seat posts that would be where I'd look.
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Old 01-16-10, 01:16 PM   #3
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Requests for weird-sized French seatposts are a common occurance around here.
I'm a little surprised some enterprising machinist with a lathe somewhere hasn't decided to whip off some 22.0, 23.4, 23.8, and 24.0 posts from some aluminum round bar stock, send them off for clear anodizing with their other stuff, and flog them on their website. It's not a difficult project, and sales would be coming in from all over the place. Guess their insurance company wouldn't like it though.
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Old 01-16-10, 08:29 PM   #4
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Just make sure you have plenty of extra post in the seat tube and use a shim.

It's perfectly safe. For proof just take a look at some of the seat posts on folding bikes.
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Old 01-16-10, 08:38 PM   #5
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Quote:
Originally Posted by Torchy McFlux View Post
Requests for weird-sized French seatposts are a common occurance around here.
I'm a little surprised some enterprising machinist with a lathe somewhere hasn't decided to whip off some 22.0, 23.4, 23.8, and 24.0 posts from some aluminum round bar stock, send them off for clear anodizing with their other stuff, and flog them on their website. It's not a difficult project, and sales would be coming in from all over the place. Guess their insurance company wouldn't like it though.
I'm going to wager not enough demand.
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Old 01-17-10, 02:04 AM   #6
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http://www.use1.com/products/seat_post_shims/index.php

shims of all sizes...
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Old 01-17-10, 03:39 AM   #7
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QBP doesn't even come close to a 23.8mm seatpost. 22mm to 25.4 is blank. Use a shim. there is no way you could open the seat-tube wide enough to swallow a 25.4mm. And unless you have some old bike-shops around with lots of old parts in dusty boxes - good luck finding an old Francaise model to match/file. So I suggest 22mm and thin aluminum. You'll have fun fitting it - so prepare for experiments.

Need a QR seatpost-clamp?

http://www.loosescrews.com/index.cgi...&id=6279015687

I checked all the usual suspects - no one carries a ready-made shim for your purpose.
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Old 01-17-10, 05:15 PM   #8
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Thanks all, I have alot of lbs's around here but none that save any older french stuff. I'll have to try shimming, does anywhere know a place i could get a good 22mm post that supports rails?
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Old 01-17-10, 05:38 PM   #9
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why don't you just use a separate clamp?
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Old 01-18-10, 04:30 AM   #10
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why don't you just use a separate clamp?
Yep - best way. It's not going to be cheap & retro - but it will work.
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Old 01-19-10, 09:21 AM   #11
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Originally Posted by Drakonchik View Post
One solution is to pull an aluminum alloy 24.0 post off another old French bike and file it down to 23.8, which entails removing just .1mm off the radius, easy to do by hand in about 1/2 hr.

If you've got a local resource with a lot of cast off seat posts that would be where I'd look.
That's the solution, but don't use a file. Use emery cloth. I've done it a few times. switch to finer grits when you get close to the size you want and then repolish the post. A pad sander will speed the process, but isn't required.

Both of these have been sanded to fit:


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Old 01-19-10, 11:35 AM   #12
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...starting from 25mm ID and up, not a lot of use to the OP.
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Old 01-19-10, 12:55 PM   #13
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I don't remember what sizes were involved, but the top one was taken down quite a bit and it took along time. The bottom one is a 26.6 in a 26.4 hole and it didn't take long at all. The idea is to keep it round by sanding it equally all the way around. Turn it constantly. Both posts need repolishing in the pictures. A few seconds with some Mother's and they'll be beautiful again. They were both used posts and the resizing eliminated the scratches.
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Old 01-19-10, 01:58 PM   #14
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Go to a bike-shop that specializes in BMX. Buy a 15/16" seatpost.
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Old 01-20-10, 04:42 PM   #15
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If I could get my hands on a 24mm post I definitely would sand it down like you described, but from my understanding, such posts are about as rare as 23.8 mm.
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Old 01-20-10, 05:03 PM   #16
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Ive got a 24mm post, but its got a rusty bolt holding it together.
Also Im in Scotland. So not much use to you.

would reaming out the frame not work?
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Old 01-20-10, 05:17 PM   #17
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Is that a Gitane service coarse?

Looks like mine without the bridge for centerpull brakes
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