I'm not a small guy and I have my seat post at full extension. I consistently find after 20 minutes of riding that it's slipped an inch or two -- just enough to give that scrunched feeling.

I've got the clamp as torqued as it ought to be. Would a longer seat post decrease wobble and hence slippage? I know some people use an extra clamp, but I'm constantly folding and unfolding as I traverse NYC. Grease seems like it would be messy.

Anyone have thoughts, or am I doomed?

Steve

About a month ago we had a post on this exact subject. One of the respondents recommended a seatpost quick release clamp. I obtained one and it works. You will have to file or otherwise remove the the lip for it to work. Just place it over the seatpost as far down as needed to bear on the Brompton seatpost clamp. Do a search for that thread.

There are several older posts on this. Try to clean (w some sort of alcohol) the post and shim.

I did that, myself.. I have 2 levers to open to fold the bike . 1 directly grips the post itself..

the 2nd one does have to be pushed down the seat post when you open the bike ..




Bike Friday Tikit folds by having the hinged seat mast pushed forward , not down, so adjusted height is fixed.

[It also will roll on its front road wheel when folded]




./.

I don't think you are doomed. You can try cleaning it but that solution did not work for me. It didn't slip as quickly but it still slips. I think fietsbob's solution of a second quick release is the most cost effective way. Purchase a 32 mm collar and grind away the lip. Even if you fold it a lot it is only one more flick of a lever. Others have had good luck with titanium seat posts but those are costlier. I am going to try the quick release method first.