The single speed anomaly

I've been commuting to work much more frequently now because it's really the best way for me to get my bike workouts in. About a month ago, I rode my single speed to work twice and figured I'd benchmark my time. My route from Leschi to Bellevue isn't very flat and has some steep hills, but I always seem to get to work faster on the single speed than on any other bike. Whah!? I don't get it. One gear and I go faster? Even with all the hills?

Last week I rode my light, carbon race bike and had my slowest commute yet. Today I rode my semi-heavy rain bike and split the difference. So basically, one speed = faster commute to work. Light, carbon bike = slowest commute to work.

Of course, when I ride the Ruby I'm usually trying to rest my legs, but I'm guessing the lighter and easier the bike becomes to ride, the more lazy I become. Interesting.