27.0mm seatpost for 27.2mm seattube?

RS wrote:
In article ,
says...


RS wrote:

Somebody gave me a nice Thomson seatpost, its 250mm x 27.0 but my
bikes all use a 27.2 seattube. They seem to clamp down ok but I'm
cautious. Any problems or issues with this? I'm more comfortable using
a 27.2 post in a 27.2 tube.

Others have suggested that this won't be a problem. I'll disagree
with them. Although the difference seems awfully small, the clamping
force required to adequately clamp the seat post will be MUCH higher
than it would be with a 27.2mm post. There's no good reason to risk
damaging your frame because you have a nice seat post that doesn't
fit. I'd suggest either shimming it, or selling it on Ebay so you can
buy a similar one in the right size.

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $795 ti frame

I think you're right, I'm going to sell it and get the right size. Anyone got a
27.2x250mm Thomson at a fair price? thanks

Why not try a shim? Easily made by cutting up a coke can with some
strong scissors. I've been using the same set-up you describe, with a
shim, with no dramas.

Donga

Gary Young wrote:
On Fri, 22 Dec 2006 10:51:43 -0700, Mark Hickey wrote:

RS wrote:

Somebody gave me a nice Thomson seatpost, its 250mm x 27.0 but my
bikes all use a 27.2 seattube. They seem to clamp down ok but I'm
cautious. Any problems or issues with this? I'm more comfortable using
a 27.2 post in a 27.2 tube.

Others have suggested that this won't be a problem. I'll disagree
with them. Although the difference seems awfully small, the clamping
force required to adequately clamp the seat post will be MUCH higher
than it would be with a 27.2mm post. There's no good reason to risk
damaging your frame because you have a nice seat post that doesn't
fit. I'd suggest either shimming it, or selling it on Ebay so you can
buy a similar one in the right size.

I've sometimes seen it suggested that you can use a knurling tool to
increase the diameter of the seatpost. Is that safe and effective?

Seatposts and seat tubes vary slightly from nominal
sizes. AFAIK, knurling is for slightly increasing the
diameter of a marginally undersized seatpost, not for
bringing it up a full size.

Soda can shims work. Given that, using an undersized
seatpost without shimming it is a bad idea. You are insuring
that the tube clamps the post only along a very small length,
which increases stress on both post and tube (though I'd
be more worried about damaging the tube or binder than
the post).