27.2 post in 27.0 seat tube

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This topic has 20 replies, 17 voices, and was last updated 6 years ago by sb.

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27.2 post in 27.0 seat tube
sl2000
Full Member

I’d like to fit a dropper post in my 2004 Marin Rocky Ridge which has a 27.0 seat tube.

I’ve got a 27.2 post (a KS Eten) but it doesn’t fit, so I need either to make the post smaller or tube bigger. I’m only 63kg so I’m guessing there’s scope to remove material from either.

Anyone have any thoughts on how I should do this please?

Posted 6 years ago

twicewithchips
Free Member

Years ago I had a Dawes (something-or-other ‘hardware’ maybe?) that had a 27.0 seat tube. We reamed it out to 27.2. It made the tube go all lumpy, either from bad reaming, or just a bad idea.

Either way, I do not recommend this route.

Posted 6 years ago

sssimon
Free Member

It’s only a 28.6mm external tube so not enough tomream really, as said above there’s a fair chance the tube will warp if you try and little margin for error.

Posted 6 years ago

FGF 701 The Hydrate Or Die Edition

wwaswas
Full Member

The tube walls on dropper posts are already pretty thin, I’d be loathe to take any more material off.

tbh, you could probably buy another 2004 frame with 27.2 seat tube for about £40 on ebay and save a lot of trouble.

Posted 6 years ago

Dickyboy
Full Member

You’d only be taking .1mm off the post that is probably designed to cope with someone at least 50% heavier than you…

I’ve done it before but not on a dropper post & will be doing it again with a shockpost for our tandem very soon

Posted 6 years ago

sl2000
Full Member

Thanks for the info – that’s ruled out reaming the frame for me.

That’s probably true! I’ve had a look though and not seen anything suitable on pink bike, and can’t see where to start on ebay. And browsing 2nd hand bikes it’s easy to escalate from wanting a dropper to pondering spending £1500 on a complete new (to me) bike.

That’s the kind of reassurance I’m after thanks.

Posted 6 years ago

Nobeerinthefridge
Free Member

I did it years ago, with a USE seatpost that was pretty lightweight as it was, exact same size issues as you.

Machined a bit off it in lathe at work, rode it for a few years, I didn’t die. And I’m 30kg heavier than you.

Posted 6 years ago

molgrips
Free Member

You can buy an extremely light and fast XC FS race frame rom 2007 for £75 with a 27.2 seatpost – from me 🙂

Posted 6 years ago

cookeaa
Full Member

It’s only a 28.6mm external tube so not enough tomream really, as said above there’s a fair chance the tube will warp if you try and little margin for error.

Most steel seat tubes with a 27.2 ID are 28.6 OD it’s only 0.1 thinner wall (0.7 rather than 0.8). About as ideal for reaming as you’re likely to find.

Perhaps only ream to the depth required for seat post insertion?
I’d talk to a frame builder, they should have the tools and be able to advise with a bit more knowledge on the topic…

Posted 6 years ago

oldnpastit
Full Member

Put an advert for a frame on the Wanted classifieds?

Posted 6 years ago

kevhl
Free Member

I’ve done this to a mid 90’s Kona frame for the same reasons. However that was a steel frame and from memory had a little more material to play with.

Posted 6 years ago

dovebiker
Full Member

Reaming out frame seattube will probably be easier than trying to put the seatpost in a lathe – plus you’ll invalidate any warranty on the seatpost

Posted 6 years ago

Nobeerinthefridge
Free Member

I’d disagree dovebiker, as long as the dropper can be disassembled, popping the lower in a 3 jaw chuck and taking that little material off would be a hell of a lot easier and a better chance of concentricity than a trying to align whacking great reamer mate.

Agree re warranty, and seatpost looks a bit shit too mind.

Posted 6 years ago

Moses
Full Member

Buy that Litespeed Niota frame in my attic.
You know, the 2006 one with a 31.6 seattube. All you need is a shim

Posted 6 years ago

bikewhisperer
Free Member

Check the seatpost with a vernier.. Many 27.2s are actually only about 27.05. You might only need to ream out ~0.1mm.

would have thought that the OD of the tube would be more than 28.6. It’s alu isn’t it?

Posted 6 years ago

YoKaiser
Free Member

I’d ream it. It is an alloy frame according to bikepedia. So plenty meat on the seattube. Take it to a frame builder on machining shop. An adjustable reamer will scoosh it. I’d take the post too btw.

Posted 6 years ago

joolsburger
Free Member

Just get this instead in a 27mm

Chart Comparison

Posted 6 years ago

sl2000
Full Member

Thanks for all the extra replies. In case anyone’s interested the bike is indeed alloy so would be thick enough to ream. I’m not fussed about the dropper looking rubbish, or the warranty. I’m leaning towards doing the frame since it might be good to still be able to use the dropper in my other bike.

Posted 6 years ago

sl2000
Full Member

This turned out to be much easier than I feared. Measuring existing and dropper posts showed 26.9 mm vs 27.2 mm – so right on the stated sizes. The OD of the seat tube is 32.0 so plenty of thickness to lose 0.15mm.

A riding buddy recommend simply using emery paper on seat tube and post – and remarkably this worked. I lightly smoothed the post, then attacked the tube with 60 grit paper and WD40. I could see the metal coming off and it only took 15 mins to get the 27.2 post fitting perfectly. And I can still use the dropper on my other bike, so perfect result.

Gratuitous success photo:

[url=https://flic.kr/p/21B8iAf]IMG_20171118_115401837[/url] by sl2000, on Flickr

Posted 6 years ago

leeerm
Free Member

+/- .2mm is usually ok as a rule of thumb.

Posted 6 years ago

sb
Free Member

Good work Simon 😉

Posted 6 years ago