From one of my Flickr and RBW group friends. I like his gear spread for a go-anywhere fixed gear bike. He’s using the Surly Dingle double-fixed cog and some larger rings than the stock Rivendell setup.
Cog 1: 17/21 Surly Dingle cog
Cog 2: 23
Gears: 46, 50, 58, 62, 71.5
I’ve migrated toward larger rings on road cranks, too, but I like his 23t flip cog better than a 15t cog. That’s a beautiful spread. He can drop from 72″ to 50″ without taking the wheel out of the dropouts. Flipping the wheel, his biggest and smallest gears have the exact same axle position.
Running the numbers, we can see that he must be using 32mm tires. And, uh, plus we can see them. 38 or 40mm tires will give slightly taller gears.