Bicycle Mechanics - Seatpost size

I have an older Parkpre MTB that I want to replace the seatpost on. When I put the calipers on it I get a reading of 25.8 mm. Looking on the Nashbar site I find several options, but none of that exact size. The 25.4 and 26.0 are the closest I can find. Would one of these work, or do I need to try to locate an exact match?

Does the current/old seatpost itself say its size? Often the exact measurement is etched on the post.

There are two Parkpre's listed in Sheldon Brown's seatpost database (http://sheldonbrown.com/seatpost-sizes.html).

If one of these is not your bike, send the size to him once you get it, so he can update the page. :)

Your LBS should be able to order most sizes for you. Get the right size seat post. It is easier than dealing with a shim on the 25.4.

There are two Parkpre's listed in Sheldon Brown's seatpost database (http://sheldonbrown.com/seatpost-sizes.html).

If one of these is not your bike, send the size to him once you get it, so he can update the page. :)

Consider also the fact that both the measuring device and the seatpost itself have manufacturing tolerances that could add up to a mm or so...

You can also take your bike to your LBS and keep trying seatposts until one fits.

Consider also the fact that both the measuring device and the seatpost itself have manufacturing tolerances that could add up to a mm or so...

Not likely. A part that is spec'ed to 0.1 mm will not have anywhere near 1 mm of tolerance. Nor will a decent caliper set. Trust your measurement.

True, I actually meant something else...
I meant that the size they're actually aiming for could be off relative to "standard" sizes. "Tolerance" was the wrong word.

But a poor set of calipers could well be off by 1 mm. All depends on the quality.
I have a plastic one (in addition to a proper metal variant) which is probably off by at least 1 mm on a good day. I use it for certain things where high accuracy isn't required, because it's light and cheap to carry around...

I have an old Puch Odyssey with a 25.8mm post and have been looking for one as well. Kalloy makes a couple models in that size. I found them at Loose Screws (http://www.loosescrews.com/) and Alfred E. Bike (http://aebike.com/site/index.cfm)

I have an old Puch Odyssey with a 25.8mm post and have been looking for one as well. Kalloy makes a couple models in that size. I found them at Loose Screws (http://www.loosescrews.com/) and Alfred E. Bike (http://aebike.com/site/index.cfm)

Thanks for the link. I didn't think of looking on the post. I'll clean the grease off of it and look to be sure.

OK, I pulled the post and sure enough it was stamped with 26.0. Hmm, I know I measured it at 25.8 so I grab the calipers and measure it again. 26.0 on the dot. WTF! Then it hits me, I measured it the first time while it was clamped in the seat tube! Note to self, remove parts from clamps before making measurements!!

Also, a lot of these seat posts are not truly round. When i was turning mine down, it was all over the place. This will, without fail, skew a caliper measurement

Also, a lot of these seat posts are not truly round. When i was turning mine down, it was all over the place. This will, without fail, skew a caliper measurement

Excellent point. I've come across the same inconsistancy when measuring seatpost diameters at various points. About all you can reliably go on is the number stamped on the old post.