Hmmm... I've been thinking about this for a while... how to commute in the winter? My only complaint about my Brompton is that I wish I could get studded or more aggressive tires on it. A 20" tire for other conditions (gravel, etc.) would be nice too. I've often wondering if Brompton would ever make an "extra-large" version of its folder with 20" tires. As long as I don't have to pack for a plane, I wouldn't mind!

So, I've kind of decided to seriously consider:
1. A fat bike. (Hey, not a folder, but might was well go to the extreme!)
2. A 20" folder like a Tern Link that can accept studded tires.

Any thoughts? Anybody with two folders for different purposes?