RE: [CR]seat post sizing

(Example: Racing:Wayne Stetina)

From: "Mark Bulgier" <mark@bulgier.net>
To: 'ADP' <aphillips9@mindspring.com>, classicrendezvous@bikelist.org
Subject: RE: [CR]seat post sizing
Date: Sat, 18 Jan 2003 12:08:02 -0800


Ann Phillips wrote
> 'Scuse my naiveté here, but wouldn't a seat post sizer tool
> like we have at our shop answer any questions?

Is that the tool with multiple short sections of different diameters? The problem with those is they only check the diameter to about 2 cm down from the top of the seat tube or lug. Fairly often you'll find that top section is flared or ovalized or otherwise warped, so the post that starts in at the top may be too large or too small for the rest of the insertion depth of the post.

There's no perfect answer though and those tools have advantages. There's no real substitute for trying the actual post you want to use, but if it's wrong you gouge up the post and can't sell it as new anymore, so anything that lets you make a more informed first guess is good.

Just try to look real close at the frame to see if that first 2 cm is really indicative of what the rest of the post will see.

Since the slot in the lug at the pinch bolt makes this top bit more variable than what's below, you need to fit the post to the part below the slot, then adjust the upper part to fit. Sometimes this means spreading the slot with some sort of pry bar. (Don't use a screwdriver unless you must, use the widest bar that'll fit, to spread out the forces and minimise marring the frame.) If the slot is too wide, the pinch bolt is usually strong enough to pull it back in.

Very minor gouging and corrosion inside the seat tube can be taken out with a Flex Hone, a relatively cheap and easy to use tool that a bikeshop might want to consider having around. Any degree of warping, bulging or ovalization needs reaming or, in some cases, blacksmithing followed by reaming. These fall under the heading of frame repairs that should be done by a framebuilder.

Mark Bulgier
Seattle, Wa
USA