Refrigerated lab tests have shown the optimum cycling temperature to be 55°. Luckily for me, it's 55° a lot in the PNW. People do notice and say, "Wow, perfect riding today!" No dehydration problems. I don't ride below freezing, because here below freezing almost always means ice. I'll ride down to about 36° and raining or spitting snow. I've ridden when it's colder and raining, but that's not so much fun. Two things make it possible: appropriate clothing and appropriate effort. IOW you gotta ride hard to stay warm. I'm usually sweating a little, no matter the temperature or rain, that's how warm I dress. However because of this preference I never wear waterproof on my torso, head, or legs.