# 1985 Mongoose ATB seatpost size?



## SeaBass_ (Apr 7, 2006)

Trying to source a longer post for my old girl. The markings have been scoured away by 25 yrs of adjustments. The 1985 Mongoose catalog makes no reference to post size. Anybody have an idea?
Thanks.


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## proto2000 (Jan 27, 2007)

I just measured mine and it translates to 25.7mm. but cannot find that size in Sheldon Browns guide so it's probably a 25.8 which seems standard. Odd size for sure. Any pics of the old girl?


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## SeaBass_ (Apr 7, 2006)

Thanks, I'll try a 25.8.
Here she is:








Found her out with the trash 2 years ago. Spent some time cleaning the chrome and giving some TLC and she shined up nice. I changed out the old hub bearings and had the wheels re-spoked in the spring. I always get a lot of comments when I ride around town.


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## girlonbike (Apr 24, 2008)

measure it!


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## SeaBass_ (Apr 7, 2006)

girlonbike said:


> measure it!


Thanks for the enlightenment.......


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## ong (Jun 26, 2006)

If you don't have calipers, most any bike shop should have them (and Harbor Freight has cheapo digital calipers for like $10). If the existing post fits fine, just measure twice (at 90° offset) and average, to account for any ovalization. It's usually a little easier to measure the exterior diameter of the seatpost than to measure the interior diameter of the seat tube.


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## girlonbike (Apr 24, 2008)

It's good advice crankpants. ride it down to the local lbs if you don't want to do it yourself.


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## proto2000 (Jan 27, 2007)

*1.013" = 25.7302mm and 1.015745" = 25.8mm*

:madman: I did measure with calipers and came up with the 25.7302mm (1.013") dimension and with a few .001's added on it rounds up to 25.8mm. Safe to say it's 25.8.


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## SeaBass_ (Apr 7, 2006)

Thanks Proto!


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## problemrider (Jul 4, 2010)

Mine's an '84 & looks exactly like yours. I just dropped a 25.4 seatpost in & it fit beautifully. Uno makes a decent microadjust in that size for about $20. It's a weird diameter, apparently a BMX standard.

The only problem: the Uno post isn't chromed like the original straight post. It's a matte alloy finish.

Btw, I slipped some red mylar Christmas ribbon around the rim & used an old Mr. Tuffy as a liner around that... looks just like the original colored Pro Class rim strips. Total cost: $4.98.

Cheers.


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## GirchyGirchy (Dec 31, 2003)

problemrider said:


> Mine's an '84 & looks exactly like yours. I just dropped a 25.4 seatpost in & it fit beautifully. Uno makes a decent microadjust in that size for about $20. It's a weird diameter, apparently a BMX standard.


Sorry for the bump, but that can't be right. I just ordered a 25.4mm Uno for my '84 and it's like the proverbial hotdog down a hallway. No way in hell it's the correct size.

I wish I'd looked more closely at my Laprade original. After looking hard enough I could make out an "8" character, and my caliper measurements match proto's. So I'm going with a 25.8mm as well.


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## jerry68 (Aug 23, 2007)

GirchyGirchy said:


> Sorry for the bump, but that can't be right. I just ordered a 25.4mm Uno for my '84 and it's like the proverbial hotdog down a hallway. No way in hell it's the correct size.
> .


Make a beer can shim... That's what we'd have done in 1984. I am pretty sure my Hilltopper still has part of a Schlitz can around the seatpost. :thumbsup:


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## GirchyGirchy (Dec 31, 2003)

jerry68 said:


> Make a beer can shim... That's what we'd have done in 1984. I am pretty sure my Hilltopper still has part of a Schlitz can around the seatpost. :thumbsup:


Ha! I'll pass, thanks.


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## Jak0zilla (May 16, 2010)

If it's simply a matter of wanting to upgrade the cosmetics of an existing post, I'd say keep whatever is in the bike now. 

Clean it up with a nickle worth of Simichrome polish (or your favorite metal polish) and an old rag. You can buff lightly with superfine steel wool to get scratches out. (Don't go nuts and reduce the diameter.) A tiny amount of grease on the seat binder bolt threads and under the bolt head, or a drop of oil on a QR release's cam will help prevent slippage.

It is A) original, and B) probably a better quality seatpost than you'll end up with these days without spending a walletfull.

Just my $.02 worth of semi-solicited advice.


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## KrisKringle (Mar 17, 2011)

Mongoose did use 25.7 which will be a hard find, most bike shops could ream it to a 25.8 though which wont be enough material to be concerned about.


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## GirchyGirchy (Dec 31, 2003)

Jak0zilla said:


> If it's simply a matter of wanting to upgrade the cosmetics of an existing post, I'd say keep whatever is in the bike now.


Mine's ovalized at the bottom, is pretty ugly, and too short as well. The seat tube on my bike was torn previously at the seat stays by someone else having the post up too high, so I don't want to get into a similar situation.

I'm going with a Kalloy Laprade, very similar to the original other than the new one not being fluted. Should look great.

Thanks for the advice, but I do have some reasons - otherwise I'd keep what's in it! Instead it'll go back into the pile of original parts from the bike.


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## ong (Jun 26, 2006)

Yeah, I recently enlarged a slightly-too-tight seat tube with a half-round file of approximately the right diameter, and it worked very well. (This was on a bike with seriously cheap gas-pipe hi-ten tubing, so your mileage may vary.) Getting a seat tube reamed generally only costs $25 or so -- I was just being cheap and lazy.

The beer can shim is a time honored solution, though! And you can order slick, production shims in a crazy array of sizes, e.g, http://www.universalcycles.com/shopping/product_details.php?id=27081. I've even had good luck with removing some material from one of these pre-made shims to get it down to a smaller effective size.

Good luck!


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