Seatpost diameter
 

I bought a new hardtail mountain bike and on the specs the seatpost is 27.2mm diameter. The seatpost for my old bike (which is longer than the one on my new bike) is about 26.8mm diameter. Do I need a "shim" to help the old one fit in or would this minor difference be sufficient? Please help!!!

Yes, you should need a shim.

What type and size of shim?

The difference (.4 mm) is not "minor" when it comes to seatposts. There are commercial shims made to do just what you want and you specify the ID (26.8 in your case) and OD (27.2 which used to be almost a universal standard) and buy the appropriate shim.

If you want to go the homemade route you need 0.2 mm (0.008") shim stock.

Go to an industrial supply store and purchase some .008" shim stock. It will come in sheet form. Wrap it around the post and mark how far around it goes. Take a ruler and mark a straight line on it. Cut on line with scissors. Wrap around seat post and stuff that bad boy down into the frame. Crack beer as reward for a job well done (and saving money). :)

The only problem is keeping this type of shim in place while you insert it and the seatpost in the frame. Commercial shims have a lip on top that keeps them in position. You could bend the top edge over to form a retaining lip.

Wrap the shim around the post and tape it in place at the top. Keeps it from squirming loose. Commercial shims are great as well if one wants to go that route.

Personally, I don't like seatpost shims. As common as 27.2 seatposts are, I'd just buy a new one in the length you need.

That is what I did; rather than go throught the trouble, I simply bought a 27.2mm x 350mm therefore negating the need for a shim.

.................just curious as to why the four-year delay in response?
A new seatpost was the right way to go.

some noob dragging up a old aka "Zombie" thread

BJC started this thread 4 years ago. And then brought it back to life today.
Not a frequent BF visitor, it appears.

Has he been riding around with no seatpost for 4 years????

That's gotta be tiring. :)

Sometimes it takes awhile for people to see the wisdom in what I say.

I don't know what the problem is. Yes, the original post is fairly old. However... Some one comes alongs and asks a question which has been asked, and answered several times- and the response is "RTFF" or, "dude, we been there, done that," or whatever. So, said poster has a question, and does the search. An old thread pops up which addresses the issue, but does not provide the answer OP was looking for. What does he do? Drag up an old thread, or start a new one and put up with, "RTFF?' He could just dredge up all the old threads and read all the responses.., but what if his question wasn't answered in a manner that made sense to him? Why don't we just answer his question, when asked, regardless of date. Here's a thought- maybe when he did the search, he didn't realize the date of the original thread, or care.

Myself I like to see some old threads dredged up. May well be a lot of good info there.

Measure your frame , or have a bike shop do that. get the right seatpost.

Kalloy makes them in all diameters and they're pretty cheap.

Interestingly in this case, it was the person who started the thread who "dredged up" this old thread. Apparently to inform me that he/she did indeed take my advice after all (it's not that surprising, see post 14).

It's kind of cool, because I had been wondering what ol' BJC had decided to do about this seatpost dilemna.