cheap seatpost replacement options - 20.5mm


New Member
Nov 24, 2003
Picked up a clunker 10speed for small commutes. Since it cost $10, don't want to invest much at all in it or put anything on it that would attract attention.

The seatpost is, as usual, the limiting factor being about 8" long. It's the style the seatpost clamp (bolted to the seat chassis (no rails)) bolts onto a still straight tube. This straight tube is 20.5mm (13/16) outter diameter at the frame and gets slightly larger (to 22.0mm) to attach to the clamp, and has no bends. Wall thickness is roughly 1.6mm.

What's a typical cheap replacement or solution in this situation? ie. raw pipe lengths. Rust resistance isn't an issue. I could even weld a pipe to bring the seat to where I need it. Future adjustability isn't an issue.

'Was thinking that a galvanized conduit or gas pipe might be an adequate replacement, and I could shim the smaller size to fit it to the seatpost bolt. Intermediate Metal Conduit (IMC) is available in OD 20.7mm thickness 1.8mm.

But, what method is used to determine if this is safe/adequate? What formula might be used that gives minimum wall thickness (for a given material) as a function of material type, exposed seatpost length, and outter diameter?

Searching for cheap seatpost replacements before, I never found anything less than around $10 at normal retail price. Nashbar became the exception with their sale recently on house brand items where they sold their posts in various diameters at around $6. But 20.5mm seems an oddball size. I also have curiosity in doing this in the future in trying to restore these clunker bikes for small distance commuters. Seatpost length often seems to be the limiting factor for taller people.