I have a 26.2 seatpost and I realy want to use it on my 27.2 seat tube.

Can I do this?

Would shims work, or is the change to great?

you can get collars and shims to use a smaller post with a larger seat tube.

I cant seem to find a shim for my sizes?

Try to see if you can find sheet metal 0.4-0.5 mm thick. Cut a piece long enough, and wrap it around the seat post. Maybe that would work?

I've never tried that myself, so I have no idea, but it could be worth a shot.

The dimensions would have to be 83 mm in one direction (that's the circumference of the 26.2 mm seat post, with a tiny margin), and as long as you feel is required in the vertical direction. I'd go for a piece long enough to give support to the seat post all the way down. Maybe 150-250 mm, depending on your bike and configuration.

Oh, and another thing! Make sure you measure both the seat post diameter and seat tube diameter to make sure you have the actual dimensions. The thickness of the sheet metal should be just less than half the difference in diameter.

correct me if I am wrong but I just checked this stuff out. I have a 26.8mm thompson post that I wanted to use on my 27.2mm. No one I could find has a shim to that size. Out of 3 different companies that make them, you can only get shims 25.2 on up and 27.2 on up. Again correct me if wrong. With that said I had a 26.8 that I used on my older 27.2 with the use of a strip of aluminum cut from a pop can and wrapped around the post. Worked like a charm and unless someone will buy the Thompson I will do that again. Mine didn't look nice but it worked.

I agree with Doco-that is how we would correct a seat post fit if necessary. Japanese built bikes in the 80's, such as Pansonic, used to come with steel seat post shims out of the box. This was on low end bikes -steel frame, steel seat post. I think that it is very difficult to make a 26.2 post fit into a 27.2 seat tube. That is a large difference. Measure everything very carefully with a good micrometer. Otherwise just buy the right seat post size. I am sure you can order a basic low price one through your local bike shop.

What you need is a piece of shim stock in 0.5 mm (or 0.02" if you are in the US). Try a hobby shop; brass is easy to work with. Just wrap it around the post and cut to size with scissors/snips.

You can use aluminum cans if you're cheap or broke. Better to use a diet soda can as not to attract bugs with sugar residue. It worked for Lemond.