It's been over 2 months now since I tried using 1500 Wet & Dry sandpaper to keep my Easton seatpost from sliding down, so when cleaning the bike last night, I took a careful look to see how the fix was holding up.
I am happy to report there is no detectable slippage at all in 2+ months, and the paper seems none the worse for wear. I like the way the paper works as a compressible shim, so the clamping pressure is spread over a larger area while avoiding any sharp pinching that might otherwise occur right under the top of the clamp.
Maybe this is a good idea for all carbon seatposts - at least on carbon frames with definite clamping pressure limits.
4 months ago