Seat Post Diameter?

[8Track]

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

[Derny Driver]

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

[P!N20]

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

[Duck!]

No such thing as a "standard" seat post diameter - they can be literally anything between 25.0mm and 31.8mm.

[WyvernRH]

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

[10speedsemiracer]

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

[uart]

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.

[MichaelB]

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