If my bike needs a 31.6mm seatpost, can I use a 30.8mm with som sort of shim? I think not but maybe I’m wrong?

old inner tube as shim? as less than 1 mm diameter difference suspect it would clamp up anyway but never tried.

A rubber shim? On a seatpost? Are you mad?

Some people hey Brant.

#tuts and shakes head#

I’m glad someone said that before I did. So Brant is there a shim I could use? Sofatester?

well use do seat post shims down to a .4mm difference but not in the sizes you want so the answer is, it’s possible.

apparently but not sure why so elaborate please

Get yer tinfoil out…. 🙂 Or buy the right size post, I hate shims, noisy and a pain even when treated nicely.

Someone’s selling a 30.8mm Joplin, My frame takes 31.6mm. Will it not rattle about and slip? {I know thesethings have isssues of reliability but keen to try one…}

you can get the replacement from 2Pure for the joplin as the internals are the same just the outer that is different .. I have both the 30.8 and the 31.6 posts but only one joplin … sadly I need the same size as you but £28 I think for other size.
Honestly I would try tape , rubber shim whatever to clamp up and think it will be ok but am clearly in a minority here.
Again why not use a rubber shim what is the problem here?
Used for seatpost mounted racks, baby cycle carriers (and at the mounting point), shims for lights etc
Could even try a coke can shim (Zen and the art of Motorcycle maintenance moment)

junkyard you’re not in the minority, there are loads of other idiots on here too. 😛

amusing but not helped to lift my ignorance!!!!

USE have made seatpost shims for years….

don’t use tape or inner tube if your gonna ‘bodge it’ try a drinks can or ask an engineer for some shim stock. It’s just thin rolled brass. for making shims from!!