theory.

So, I've found over the years that riding a bike in the winter is substantially more difficult than when it is of moderate temperature outside. Is it a purely psychological ordeal? Is there something more to it than that? I'm not a scientist, trust me, but I would venture to claim that colder air is actually more difficult to ride through on a molecular level. Don't molecules get closer together as they get colder? Wouldn't molecules being closer together be more dense? Aren't things that are more dense harder to work your way through? Isn't that why running in water is so damn much harder? I don't know. You tell me. Go get scientific and tell me I'm right. I dare you.