This morning was the first warm weather commute for me this year. I pretty much took the winter off, but have been getting back into it over the last few months.
So far every ride in has been under 40 degrees. My usually kit in such weather consists of a pair of cotton sweats over cycling shorts, long sleeve lycra shirt, fleece jacket and if it's below freezing, a nylon windbreaker.
Outfitted in such a way, I take the better part of 50 minutes to make the 12+ mile commute.
Last summer I was able to do it consistently in 37-40 minutes. I attributed my cold weather times mostly to being an out of shape fatty.
This morning, I was back in just my cycling shorts and long sleeve lycra and I was back down under 40 minutes.
Does temp really matter that much? The extra weight isn't much.
I suspect the big difference is aerodynamics. Smooth lycra cuts through light warm air quite a bit better than loose fitting fleece through heavy cold air.
Makes me think that spending a few bucks on some cold weather cycling gear might get me out therer more often next winter.