I used to go mountain biking with a group of guys every single Saturday no matter what. Cold weather was simply NOT an acceptable excuse for missing. You'd get laughed at every single week until somebody else had an unexcused absence. I don't know what our coldest ride was but I know it was sub zero. I had some 3 finger mittens for my hands but feet are the hardest to keep warm. The most uncomfortable weather, by the way, is temperature in the 30's but with rain.

This winter I told Mrs. Grouch that my current go/nogo line for riding is 30 degrees. I have no doubt I could do it but riding in weather colder than that would require buying some different clothes.
Actually, 40 degrees sounds a lot better to me.