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shibbie 04-21-12 07:40 AM

Old Peugeot Seat Post replacement
I just bought a pretty awesome looking Peugeot Tourmalet of unknown age (ebay seller thought 70s, but the decals look 80s and someone more knowledgeable than me said the kind of lugging wasn't done until the late 80s). Everything looks in good working order - except the seat post is super scratched and I can't get it down far enough to fit me. I did a rough measurement and believe it to be 25.00 mm (although it could be 25.4 mm). I have a few questions about replacement:

a) Do I have to find a vintage seat post or will new ones be compatible?
b) Does size matter? They come in different lengths. How do I know if something will be too long or too short?
c) I'm on a budget and the cheapest ones seem to be aluminium. Does that matter given my bike is steel? This is just a city commuter bike that won't get more than 30 or so miles a week so comfort isn't my biggest concern.
d) Is there any surefire way to know seat post size? Like is it printed somewhere or is my ruler the best I can do?
e) Are there any other parts I need in addition to seat post to make this happen?


HillRider 04-21-12 07:50 AM

a. A new seatpost will be fine
b. Length doesn't matter as long as you have enough to have the "minimum insertion" mark below the seattube's top. Too long could hit the water bottle braze-ons inside the seat tube but that can be corrected with a hacksaw.
c. Aluminum is by far the best material for a seatpost. They come in both cheap and expensive models and can be used in a frame of any material. Be sure to grease it to prevent corrosion and binding.
d. A bike dealer should have a gauge that will give you the correct seatpost diameter for your frame. Seatposts themselves usually have their diameter engraved on them below the minimum insertion line.
e. Do you have the clamp bolt for the frame?

shibbie 04-21-12 08:13 AM

Thanks for the info, Hillrider. I do have everything that was originally there.

zukahn1 04-21-12 08:37 AM

If your not sure on the size of seat post you should probably take it to a shop and have the size checked. A lot of Peugoets took none standard size or type posts.

fietsbob 04-21-12 08:42 AM

Given 25,4 is an inch , and one thing the French have favored is the Metric system,
with it's Napoleonic Origins.. so Id vote even 25mm.
Kalloy makes decent seat posts starting at 25,0., some 23mm..

Wait till you seek out stems and find out their penchant for being the metric outlier .
22.0 stems are quite uncommon, as replacements, these days

jyl 04-21-12 09:03 AM

That seat post would likely be aluminum, which is the best material.

You should be able to remove most of the scratches and restore the post to gleaming condition, with a couple hours' work. Search here about polishing.

Can't get the post down far enough - hmm, is the bike too big for you then? How low are you trying to get the seatpost - measured by inches of post you want to leave exposed above the top of the seat tube?

Anyway, pull the seatpost out, sand/polish it smooth and shiny as above, grease it (liberally!), and try re-inserting it. It should go all the way in. You can cut off the end if absolutely necessary, but that should not be necessary and is to be avoided if possible.

Peugeots used 24.0 mm, 25.0 mm and I've seen 22.0 mm and heard of other oddball sizes. Have it accurately measured. A fair number of options at 25.0 mm, much fewer at 24.0 mm.

MilitantPotato 04-21-12 12:44 PM

It'd be a good idea to have the seat tube scrubbed of rust. I'm having a brain fart on the name of the bit, but it's more or less steel wool on a rod. That may let ya get the seat post further into the frame.

If you're hacksawing the post shorter as jyl mentioned, be sure the post goes an inch or two below the seat-stay and top tube junction.

Also as jyl said, accurate sizing is important. Having a post .2mm too small is a lot.

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