Interesting topic considering my latest observations. I am unsure of your experience level with winter riding. I am entering my 4th winter of almost daily riding, regardless of conditions. I usually leave early in the morning for a 20-25 mile mountain bike on rock roads, this time of year.

I have one very common route that i ride in both winter and summer. It is about 22 miles and in the Summer it takes me around 1 hr and 30 minutes normally. Today, and a few of the other recent cold days it has taken around 1 hour and 45 minutes.

It is well known that travel is slower in the cold temps. Many reasons are given but none is particularly well proven. What i can tell you is that not only is winter riding slower, but it also consumes more energy, substantially more in some cases.

I am pretty tired this evening. The last several mornings have been our coldest so far this year. This morning was 24 F, and again i was riding for 1 hr. 45 minutes. I suspect that there are other biological factors involved that probably no one knows about. I just always have a bit less energy when the daylight hours start to fade. Perhaps our bodies are more reticent to spend energy and more apt to try and conserve it? Whatever the cause, i think what you are feeling is normal.