logdrum

I think just the work that the body has to do to keep you warm burns enough calories to offset the higher food intake in Winter! The workout from the actual cycling is additional.
Northern New Mexico (Albuquerque Area) has a relatively cold winter this time. Hey at one point we were even colder than Denver! I try to commute 4 times a week and at least one long weekened ride. This place is cursed by winds and I think 1 - 4AM is the only time when the wind dies.

I don't think about efficiency anymore but I did clock myself going to work 7.6 miles in 22 minutes and that includes a 300 ft climb for less than half a mile, maybe 5-8 mph cross head wind too. I was riding single speed as well -- not really slower than my summer riding but I think the winds are really terrible here in the summer!

I think the urgency to get out of the cold actually helps me to pedal through inspite of all the weight friction etc etc.

Both my fixed gears have cheapie computers that I've converted to read RPMS and I think I managed 110 in the winter and 130 in the warm seasons when on flat and moderate rolling hills. Not a 30% decrease really!