Because my ride to work is all downhill (and of course uphill on the way home),I ride a four speed fixed gear. It's a mongrel Rickert road bike with a Dura-Ace crankset (40/42) and a Sanshin Pro-Training rear hub. Rather than the typical double-sided hub threading, this hub has room for 2 cogs and lock ring on the right side only. I have 16/18 back there. So, to work I ride the 42/16, on the way home, it's 40/18. Piece of cake!
Sunny Arcata, CA