I commute along the same route regularly, and for some reason it seems like my commute takes less time - and less energy when it's raining heavily (but calm) than when it is sunny and calm. Last night I rode home from my office in the rain, and I actually shaved 5 minutes off my usual 40-minute commute. This morning, I talked with a fellow commuter at my office, and he mentioned that he also made better than average time heading home last night.
There was no noticeable wind, and our route takes us both over a substantial hill, both of which would negate wind effects. Is it possible that:
a) water on the road reduces friction and rolling resistance on our tires?
b) raindrops of a certain size and frequency create turbulence in the air, reducing air resistance?