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