I have noticed a rather large difference in the efficiency of my Birdy when compared to my road bike. The Birdy rolls down (slows down) more quickly when coasting on flat terrain, which indicates more rolling resistance. I use Kojaks inflated to 120 psi (no flats at all after nearly a year of heavy riding), with the standard 18" wheels and Shimano parallax hubs. The 10 speed XT drive line is about as efficient as the Record kit on my road bike.

Obviously, it is easier to maintain speed on my road bike, and for the really long rides it remains my top choice. But for getting around town, or when I want to ride in far-off places that I must get to by train or bus, the Birdy is my first choice.