Seat Post Diameter?

8Track
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Seat Post Diameter?

Postby 8Track » Wed Oct 24, 2018 10:56 am

Hi all,

I was thinking of buying a Suntour GPX seat post for my 1989 Elan. The Suntour post is 27.2mm - the standard size.

Before purchasing though, I thought I'd measure my existing post. My calipers measure it's diameter at 26.4mm.

Now I don't know if its just a measurement discrepancy, or if my frame can accommodate a 27.2 post.

Seat tube outer diameter measures 28.9mm and is made from Tange 5 tubing.

Any wisdom you could share would be appreciated.

Thanks,

Mark

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Derny Driver
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Location: Wollongong

Re: Seat Post Diameter?

Postby Derny Driver » Wed Oct 24, 2018 11:17 am

If it measures 26.4, it needs a 26.4 size post. Nothing else will fit.
But the only real way to tell is to try a few different size seatposts in there. Some tubes may have been reamed - there is no way to tell. Even measuring the top opening may not be accurate.
I keep old seatposts of different sizes to test the frames I buy. I have posts in 26.4, 26.8, 27.0, 27.2. My latest aquisition is a 26.2 but I managed to find a seatpost to fit it on Ebay. I make things hard for myself by always trying to match the seatpost to the groupset.
Save your Suntour post for another frame. If you have Japanese components then maybe you can find a SR post in 26.6
Last edited by Derny Driver on Wed Oct 24, 2018 9:51 pm, edited 1 time in total.

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P!N20
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Re: Seat Post Diameter?

Postby P!N20 » Wed Oct 24, 2018 11:21 am

The internet tells me the Tange 5 seat tube is 28.6 OD and 26.8 ID.

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Duck!
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Re: Seat Post Diameter?

Postby Duck! » Wed Oct 24, 2018 12:43 pm

No such thing as a "standard" seat post diameter - they can be literally anything between 25.0mm and 31.8mm.
I had a thought, but it got run over as it crossed my mind.

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WyvernRH
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Location: Newcastle NSW

Re: Seat Post Diameter?

Postby WyvernRH » Wed Oct 24, 2018 1:14 pm

Derny Driver wrote:But the only real way to tell is to try a few different size seatposts in there. Some tubes may have been reamed - there is no way to tell. Even measuring the top opening may not be accurate.
I keep old seatposts of different sizes to test the frames I buy. I have posts in 26.4, 26.8, 27.0, 27.2.



All true, but you could go to Bunnings and buy a set of internal calipers, take a few readings below the seat clamp slot and take the average. Should be pretty close that far down the tube.

Richard

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10speedsemiracer
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Re: Seat Post Diameter?

Postby 10speedsemiracer » Wed Oct 24, 2018 1:35 pm

How weird, the only Tange #5 I've had used a 26,6mm
Mmm, SunTour

uart
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Re: Seat Post Diameter?

Postby uart » Wed Oct 24, 2018 9:21 pm

8Track wrote:Before purchasing though, I thought I'd measure my existing post. My calipers measure it's diameter at 26.4mm.

See 10speed's post above. It's 26.6

A 27.2 post definitely will not fit.

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MichaelB
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Re: Seat Post Diameter?

Postby MichaelB » Thu Oct 25, 2018 8:34 am

uart wrote:
8Track wrote:Before purchasing though, I thought I'd measure my existing post. My calipers measure it's diameter at 26.4mm.

See 10speed's post above. It's 26.6

A 27.2 post definitely will not fit.


Sure it can.

Just need a bigger hammer. And a file. And another bike and seatpost.

Hope that was useful :roll: :lol:

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