About twenty years ago I bought a bike from a friend of my brother’s. He was trying to get a custom frame shop off the ground and he built me two frames from Columbus El/OS steel.

Great bikes. Many fun miles.

I realized that my seat was not moving up and down as well as it should this weekend. I also realized that I hadn’t greased the seatpost in too many years.

Pulling it out was difficult. Really difficult. Really difficult.

Here’s the rub. I have a Thompson seat post (SP-E124) 28.6mm x 410mm, model number 12263.

The seat tube opening, no compression, is at 30.25mm. (The clamp ring is welded onto the frame.)

Problems:
The current shim is 50mm long. From what I’ve read, you want the shim to extend past the joint of the seat tube and the downtube. This isn’t even close. I need a longer shim, say 100mm.

The current shim has walls that are 1.3mm thick, which I think is the major problem. If the post is 28.6 and the shim adds 2.6mm, I’m at 31.2mm. No wonder it’s tough to get in and out. I need a thinner shim, one that takes me from 28.6mm to 30.25mm; basically one that adds 1.6mm to the post.

Looking at various bike supply sites, a post at 28.6mm seems to have gone out of style (they’re not made any more), so it doesn’t seem as though I can buy a ready made product. I’d also note that Thompson seems to be pretty clear that they don’t recommend using a shim with their posts but that ship has sailed.

Question: what would be the problem with buying this product? It would get me really close to the right width (30mm). Would it be wide enough? Would clamping make up the difference? Would it rattle in the frame?

I realize I’m trying to solve a problem created within the design. But I really just want to ride my bike without worry.