My total round trip distance is 18 miles. I can get to work in about 20 min. if I'm really moving and have no headwind. It takes me twice as long to get home under the best circumstances. The reason for the difference?

About a 800 vertical feet over the nine miles, most of it in one single mile long hill. No stop signs and no traffic lights. It's almost all rural state highway with a "bike lane" shoulder. So 18 mph., averaged over the entire commute, would be my approximate fastest commute time but the morning half is at an average of 26 mph and the return trip at an average of 12 mph. But at the fastest point of the morning commute I'm going about 40 mph and for the same distance on the homeward leg it's more like 6 mph.

The ride? a Bridgestone MB-1, rear rack and panniers, flat bars with Scott aero bars, Schwalbe Marathon tires during non-winter and Schwalbe M Winters during the cold months (probably 6-10% slower at those times).